XEW BOOKS

---

XEW BOOKS A Treatise on Physical Chemistry. Edited b y H . S . Taylor. 2 8 x 1 6 cm. p p . Vol. I , 662; Vol. 11, 709. New York: D. V a n Nostrand Company, 1924. Price: $12.00. Thisis a co-operative work because in this way one can get a more authoritative presentation of the different fields and because it is possible to get the work done more rapidly by distributing it. The chapters in the first volume are: the atomic concept of matter, by H. S. Taylor; the energetics of chemical change, by H. S.Taylor; the gaseous state of aggregation, by Otto Maass; the solid state of aggregation, by Otto Maass; the liquid state of aggregation, by R. N. Pease; thermochemistry, by A. L. Marshall; the laws of dilute solutions, by J. C. IT. Frazer; homogeneous equilibria, by Graham Edgar; heterogeneous equilibrium, by 4 . E. Hill; the measurement of electrical energy, by G. A. Hulett; conductance, ionization, and ionic equilibria, by J. R. Partington. The chapters in the second volume are: the electrochemistry of solutions, by H . S. Harned; electrometric methods in analytical chemistry, by N. H. Furman; reaction velocity in homogeneous systems, by F. 0. Rice; reaction velocity in heterogeneous systems, by H. S. Taylor, the quantum theory in physical chemistry, by Saul Dushman; the third law of thermodynamics, and the calculation of chemical constants, by JT7. H. Rodebush; photochemistry, by H. s. Taylor; infra-red radiation in chemical processes, by H. A. Taylor; colloidal chemistry, by W. A. Patrick; radiochemistry, by S. C. Lind. Taylor considers, p. 54, that oxyhydrogen gas is reacting slowly all the time, and points out, p. 66, that if one million molecules of hydrogen are reacting with oxygen per second in a gas mixture, it will be sixty million years before there is a volume contraction of one cubic centimeter. Taylor and a few-not all-of his fellow authors mis-spell Helmholtz’s name consistently, p. 12. I t is not clear from the text just what the first law of energetics really is, pp. 34, 36, or why it should not be called the first law of thermodynamics. If the calorie equals 4.182 joules, then the joule equals 0.2391 calories and not 0.2423, p. 36. Maass rejects Lehmann’s view that the substances forming “liquid crystals” melt first of all to form large aggregates, each of which is a crystal, the disappearance of turbidity being accounted for by the melting of these small crystals in turn a t higher temperatures, p. 32. “This explanation is in opposition to the kinetic theory conception of a liquid. The liquid crystals would have to be enormous aggregates in order to give the optical phenomena observed. Yet, these liquid crystals have low viscosity (whereas liquids with large molecular weights have very large viscosities), and their variation of molecular surface energy with the temperature is in agreement with this low molecular weight. In fact, the variation of their physical properties, except for the rather sharp disappearance of turbidity, is continuous. I n order to correlate his theory of liquid crystals with the properties of ordinary liquids, Lehmann was willing to abandon the whole kinetic theory of liquids. The real explanation of liquid crystals is given by the regional orientation of the molecules of the liquid taking place in a manner discussed above, an hypothesis which was put forward for the first time by E. Bose.” When a given film of palmitic acid, spread over a ?;/IOO HC1 solution, is kept under a constant force of 1.4 dynes and is heated, there is a sharp expansion between 28’ and 35”, followed by a small steady expansion above 35”, p. 139. “The expansion coefficient above this temperature corresponds in magnitude to the thermal expansion coefficient of a gas. A change of state evidently occurred, analogous to the change of solid to gas.” When considering the latent heat of a liquid, Nills assumed that the force of attraction varies as the inverse square, p. 142. “In a recent paper, Edser has criticized these deductions on the ground that the variation of the constant with the temperature was neglected. He points out that the inverse square law obviously cannot hold and that the agreement obtained by Mills was due to the variation in molecular force of attraction with the temperature which just compensated for the error involved in using the inverse square law. . .Ed-

NEW BOOKS

357

ser shows that the surface tension is equal to the intrinsic pressure multiplied by the diameter of the molecule and a known function of n where n is the power in the inverse distance law. By using the known values of the surface tension, the internal pressure given by the above equation, and an approximate value for the molecular diameter, sixty-five different substances gave the most probable value of n as being eight, so that the attraction apparently varies as the inverse eighth power.” Maass accepts the Ramsay and Shields formula as giving molecular weights of liquids, p. 127. He refers to the abnormal higher values of the constant obtained by Walden and others; but does not discuss them. Pease says, p. 173, that “one reason for the partial failure of the law of Dulong and Petit lies in the arbitrary choice of room temperature as the temperature of comparison. Investigation of the change of the heat capacity with temperature has revealed that this law is subordinated to a more general one which states that atomic heat capacity a t constant volume increases with the temperature to a maximum value which is in the neighborhood of six degrees per calorie for all substances. This constant maximum has already been reached a t room temperature by those substances which obey the law of Dulong and Petit, and then heat capacities are nearly independent of the temperature a t room temperature. The heat capacities of those other substances which deviate from the law are still incieasing more or less rapidly with the temperature and presumably will reach a maximum a t much higher temperatures. Thus, for example, the atomic heat capacity of diamond has risen to 5.45 calories per degree a t I 169”K,from the value of 1.6 calories per degree a t room temperature.” A forward reference to p. I 167 would have helped the reader. Pease wishes to substitute the words “mesomorphic state” for the term “liquid crystals,” p. I 7 5 . “Mesomorphic substances are obvioudy not crystalline in the ordinary sense, nor are they under an externally applied stress. To account for their bi-refringence and therefore their anisotropic character, it seems necessary to assume that the molecules of such substances are not distributed a t random as in an ordinary fluid but in some regular manner, however primitive the arrangement may be when compared to the arrangement of atoms in crystals. This assumption of molecular orientation is further borne out by the interesting forms which liquid crystals assume. Perhaps the most extraordinary of these are the socalled graded drops (Zes gouttes d gradins). When a small mass of ethyl para-azoxybenzoate, for example, is fused on a carefully cleaned glass plate or a freshly-cut cleavage surface of mica, it does not wet the surface but draws up into a drop whose upper edge is smooth and perfectly plane and whose edges are graded off into steps. The drop appears to be built up of a pile of planes which, when the drop is touched, glide over one another easily and recall the cleavage plane of crystals. I t appears probable that these planes are of molecular dimensions in thickness (about 5hp). Their edges are made visible under the microscope by the fact that they are terminated by chains of very fine droplets which are bi-refringent,” p. 176. It is a pity to make the unqualified statement, p. 169, that “of two polymorphic modifications, that which is metastable in the melting point region has the lower melting point.” This is not necessarily true in case there are two modifications in the melt. Marshall has some very interesting pages on the heats of adsorption, pp. 220-223. Fraser defines a solution, p. 232, as a one-phase system consisting of two or more molecular species not transformable one into the other. This of course makes mixtures of gases gaseous solutions. The chief difficulty with the definition is in the application of it in these days of colloid chemistry. Unfortunately, Frazer does not give us any clue as to how we are to recognize a one-phase system. That can hardly be held up against him because nobody has a definite criterion as yet. On the other hand we may hold it up against Frazer that he cites Ostwald’s whirligig proof without comment, p. 239, and that he implies, p. 275, that van’t Hoff was hazy as to the volume term in the osmotic pressure formula. The Donnan equilibrium is treated a t considerable length, pp. 283-290. Edgar introduces us to the mass law, p. 292; but points out, p. 299, that “for many purposes it is convenient to consider the question of equilibrium in chemical reactions from the standpoint of the ‘activities’ of the reacting species.” This is true enough; but the reviewer still feels that the activity is merely the figure which one has to substitute for the experimen-

3 58

NEW BOOKS

tal one in order to make the equation come out right. There is a good table for the ammonia equilibrium, p. 334, and attention is drawn to the fact that the equilibrium constants for the ester formation are not the same for the liquid and the gaseous phases, p. 338. It might well have been added that one would get a third equilibrium constant in case two liquid layers were formed. The peculiarities of the distribution of silver perchlorate between water and benzene, water and toluene, and water and aniline are discussed, p. 358; but there is no explanation for the phenomena. When a small amount of silver perchlorate is added, the salt passes wholly into the water in the first two cases and wholly into the aniline in the third case. The word “isopleth”, p. 400, for a line of equal concentrations, was new to the reviewer. Edgar does not believe in the constancy of the solubility product, p. 459. Hulett has a short chapter, pp. 469-483, on the measurement of electrical energy. He, of course, favors making the volt and the ohm the primary units, and the ampere the derived unit. Some day this will be done; but electrical congresses meet seldom and act slowly. Partington has a statement, p. 487, which is quite thrilling if true, that “some sulphides conduct metallically and others electrolytically, both solid and in the state of fusion.’’ The reviewer fears, however, that Partington does not mean to say that some fused sulphides conduct metallically. It is interesting to read, p. 496, that “the influence of an added metal on the conductivity of a liquid metal is quite independent of the conductivity of the added metal. The determining factor seems to be tendency to compound formation. The alkali metals, having a strong tendency to combination, always lower the conductivity of a liquid metal to which they are added, whilst indifferent metals may either raise or lower it.” “Electrolysis of solutions of lithium carbide in molten lithium hydride leads to separation of carbon a t the anode, whence it is concluded that the carbide is ionized. Nitrides of alkaline earth metals in the corresponding hydrides as fused solvents appear to be similarly ionized”, p. 504. Partington adopts the German spelling of cathode, p. 505, and not Faraday’s. This error is now almost universal in England. Harned follows Lewis very closely in his data on electromotive forces, making use of activity coefficients, p. 794, and considering the zinc electrode as positive, p. 798. Most of us used to do this; but it would have been better a t least to have indicated that this had been given up officially in England and in Germany. Reference is made, p. 813, to the fact that an alternating current superimposed on a direct current lowers the overvoltage; but both overvoltage and passivity are considered as unsolved theoretical problems, p. 8 2 2 . “The preceding brief discussion of the phenomena of overvoltage and passivity has indicated that, up to the present time, explanations of the cause of these behaviors are divided principally into two distinct types. The first attributes the cause to the formation of chemical substances on the electrodes. I n such cases as the anodic passivity of lead, this point of view seems to be unquestionably valid; but, in such cases as the anodic passivity of iron, the presence of an unstable compound cannot be regarded as established. The second theory takes these phenomena to be examples of irreversible processes, to depend on unstable physical states produced by electrolysis, and to be explained in terms of the velocities and catalytic acceleration or retardation of the electrolytic processes involved. Such theory, although based on assumptions regarding the inner mechanism of the processes which must be regarded as highly conjectural, has been shown by Smits to be consistent with the laws of thermodynamics.” Rice does not approve of the Arrhenius method of accounting for the change of reaction velocity by postulating the existence of an active and an inactive form, p. 901. “Several objections t o this hypothesis are immediately apparent; the assumption that the catalyst increases the rate of a reaction by shifting the equilibrium between the active and inactive molecules is contrary to one of the conceptions of catalytic activity, which is that a catalyst does not affect the equilibrium point of a reaction in dilute solution; further, the assumption that substances like cane sugar, ethyl acetate, etc., exist in two forms in solution is very artificial and is without experimental support; indeed, when considering multimolecular reactions we have nothing to guide us when selecting the reactant which is supposed t o be present in two forms. For the r e a c h n between cane sugar and water catalyzed by hydrogen

NEW BOOKS

359

ion, we might select an;? m e of the three entities taking part in the reaction and by saying that it was present in two forms, active and inactive, we could deduce the Arrhenius empirical equation; there would perhaps be some justification for saying that the water exists in two forms, active and passive, for liquid water is ordinarily supposed to be a mixture of simple water molecules and various polymers; we might therefore postulate that the simple water molecules are present in very minute concentration and are the active molecules in the hydrolysis. This would account for the high temperature coefficients of hydrolytic reactions but it would also follow on the basis of this hypothesis that all hydrolytic reactions would have the same temperature coefficient; since this is not, the case we cannot derive the empirical Arrhenius equation by postulating that the water is present in two forms. The remaining possibility that the hydrogen ion exists in two forms will be considered later. “The Arrhenius hypothesis can hardly be regarded as anything more than an ad hoc explanation of the difficulty; from it we can conclude that each chemical reaction has a unique temperature coefficient depending on the heat of activation of the active molecules of the substrate but there does not seem to be any way of developing the hypothesis so that it can be tested.” Rice is assuming here that the active form is an ordinary chemical substance. Most of his objections vanish if we follow Baly’s lead and consider the active form as due to the opening of the fields of force. The experiments of Van Name and Edgar on the rate of reaction of metals with iodine dissolved in potassium iodide, p. 94j,are very conclusive as to the existence of a diffusion layer in this case. The work of Xacken on the rate of growth of crystal faces, p. 950,was new to the reviewer. Very interesting also is the discussion, p. 974, of the rate of sublimation of small spheres of iodine. The work of Knudson, Wood, and Langmuir on the velocity of condensation is given, p. 976, and Iredale’s work on the adsorption of methyl acetate vapor on mercury, p. 1001. Dushman says, p. IOOS,that “our whole conception of atomic structure, of the mechanism of chemical and physical reaction of the significance of the laws of thermodynamicsall our previous ideas on these subjects have been completely revolutionized through the application of the quantum theory. Indeed, just as in the past we have had in the history of chemistry the period of the phlogiston theory, that of the dualistic hypothesis and so forth, so the historian of the future will undoubtedly be justified in designating the present as the period of the quantum theory.’] Dushman closes the chapter, p. 1130,by saying: “Bohr’s theory has been extended to the explanation of band spectra in terms of quantized molecular rotations. I t may, in the near future, even be possible to treat chemical reactions as transitions between stationary states defined by certain quantum numbers and energy levels. The views initiated by Bohr have affected fundamentally all our previous ideas on atomic structure and radiation phenomena. But this is only a beginning and there is still with us the whole field of chemical phenomena in which there is plenty of scope for the extension of the same conceptions, and the results achieved in this manner will no doubt be just as wonderful and epoch-making as those already accomplished in the above-mentioned fields of investigation.” If the reviewer understands the situation rightly, the chemist has always played with quanta, though he did not call them that. The use of the equivalent weight and of the ion has meant a discontinuous absorption or emission of energy, though without the assumption of resonators, it is true. As for energy levels that has been a common-place to the chemist ever since it was shown that the electromotive force was a measure of the chemical affinity. I t is true that the chemist did not express energy levels in terms of orbits; but that does not seem absolutely essential. Rodebush has written an admirable chapter on the third law of thermodynamics. The reviewer was especially interested in the paragraphs on the heat capacities of supercooled liquids, p. I 142;in the heat capacity curves for metals, p. I 14j;in the decomposition data for nitrates and carbonates, p. 1162; and in the relative heat capacities of graphite and diamona, p. I 166. On this last page Rodebush says that “the third law tells us that endothermic compounds are unstable a t low temperatures; but the common belief that endothermic compounds are stable a t high temperatures is scarcely more than a superstition. The

360

NEW BOOKS

important factor is AC, formation and, even if it be positive, the compound will probably cease to be stable due to other reactions. I n the sun, for instance, not only do molecules disEociate into atoms but atoms dissociate into electrons. Our generalizations in regard to specific heats assume that they approach the Dulong-Petit value as a limit a t high temperatures; but this is only true for a short temperature interval. At still higher temperatures the amplitudes of vibration of the atoms become so great that the motion ceases to be simple harmonic, and dissociation analogous to evaporation takes place.” ‘When a metal is heated to a sufficiently high temperature, electrons are emitted in a manner that appears exactly analogous, from the standpoint of the kinetic theory, to the evaporation of molecules from the surface of a solid. There appears to be a definite heat of evaporation and a definite vapor pressure of electrons which increases with the temperature according to the well-known thermodynamic laws. Laue has shown that, under suitable conditions, the swarm of electrons emitted may be treated as a gas,” p. 1192. Taylor has written a good chapter on photochemistry; but the quantitative side overbalances the qualitative one too much for the reviewer’s taste. Einstein’s law of the photochemical equivalent is very important, p. 1210; but one should begin with depolarizers. The reviewer was interested in the statement, p. 1212, that short wave-length light produces both ionization and ozonization of oxygen, but that the two phenomena are independent. Weigert showed, p. 1232, ‘‘that phosgene, which is a colorless gas absorbing in the ultraviolet only, can be decomposed photochemically by visible light when chlorine is added to the phosgene. The chlorine absorbs the blue light and this energy is transferred by some mechanism to the phosgene, bringing about its decomposition. Weigert showed that this photo-sensitization is quite a general phenomenon in that the decomposition of ozone can be made sensitive in the visible region by addition of chlorine or bromine, the combination of hydrogen and oxygen and of sulphur dioxide and oxygen can be sensitized to visible light by chlorine.” Patrick defines solutions containing particles larger than single molecules or ions as colloidal solutions, p. 1277. He proposes to give a discussion of the theoretical aspects of colloidal chemistry. By a theoretical treatment he means the correlation of as many of the facts of descriptive colloidal chemistry as possible with a few fundamental assumptions, p. 1278, developing the theory of colloids around the postulates of molecular attraction and molecular kinetics, p. 1284. To what extent he succeeds in doing this will be left to the reader. There is one place, however, where the reviewer wishes that a little more detail could have been given. Patrick accounts for the red color of certain gold sols by saying that there is a strong absorption band in the green, p. 1307. It would have been shorter and just as helpful to have said that they are red because they are red. What one wants to know is why finely divided particles of gold should absorb green strongly, when green is the color for which massive gold is most transparent. Professor Taylor has done a good piece of work in getting this book written. It should be very helpful to students. The reviewer would not have objected to a somewhat less mathematical treatment; but he recognizes that he is a hopeless extremist on this point. This book is certainly exactly what many people want and that is, after all, what the editor was trying to furnish. Wilder D. Bancrojt Photography as a Scientific Implement. By Charles R. Gibson and others. 63x16‘ cm. pp. niii+549. New York: D. V a n Nostrand Company, 1963. Price: 89.00. The object of this book is to bring together in accessible form the methods of photographic technique developed by experts in astronomy, surveying, aeronautical observation, microscopy, metallurgy, engineering, physics, and other spheres of research. The chapters are: the history of photography, by C. R. Gibson; the elementary optics of photography, by S.E. Sheppard; photographic optics, by A. E. Conrady ; the theory of photographic processes and methods, by S.E. Sheppard; astronomical photography by C. R. Davidson; application of photography in physics, by H. Moss; photography in the engineering and metallurgical industries, by J. H. G. Nonypenny; photomicrography, by G. H. Rodman; photographic surveying,

NEW BOOKS

361

by H. S. L. Winterbottom, aeronautical photography, by F. C. V. Laws; colour photography, by W.L. F. Wastell; photography applied to printing, by W. B. Bishop; the technics of kinematography, by A. S. Kewman; the camera as witness and detective, by IT‘. M. Webb. Surprise is expressed by Gibson, p. 19, that Wedgwood and Davy did not succeed in washing out the unchanged silver salt and thereby fixing the image. As a matter of fact they tried to, p. 14; but were not able to wash out all the silver nitrate in spite of its solubility. This was evidently due to the adsorption of silver nitrate by the material. Under photographic optics, p. 52, it will be news to most people that “the natural sea horizon is not straight; it has the curvature of the earth, and from a high viewpoint this is extremely obvious even to the unaided eye.” On the next page, p. 5 3 , we read that, ‘(tosecure the conventional and pleasing representation of buildings and tall natural objects, the sensitive plate must be in an accurately vertical position and not tilted. In portraits we assume that they represent the original as seen from a distance of ten feet or more; the unnatural appearance results when the lens is Dlaced within a few feet or even less of the victim. The misleading effect of photographs of steamerinteriors is due to the use of wide-angle lenses; the pictures produced by painters and artists hardly ever embrace an angle of more than 30’ or 40”, and accustom us to viewing pictures from a distance yielding a subtense not exceeding that angle. For that reason photographs covering a much larger angle never give a correct impression. As most people cannot see distinctly objects a t a distance less than eight or ten inches from the eye, all pictures taken with a lens of a focal length below this minimum cannot be viewed from the proper distance, and therefore never look right until they are enlarged or magnified optically. That is the heavy penalty attached to snapshots taken by small cameras. I t will thus be seen that the unsatisfactory types of photographs, whose perspective is usually condemned, are due to offences against well-established and thoroughly justifiable artistic conventions; the proper application of these conventions naturally is left to the user of photographic lenses. The designer can only render the perspective geometrically correct according to the criteria deduced above; when he designs a wide-angle lens, he knows perfectly well that the vast majority of the images (they can rarely be called pictures!) produced by them will be caricatures of the original subjects, but he has to meet a demand and does his best.” Sheppard’s theory of ripening the emulsion, p. 131, is that “the chief function of ripening, which may also be effected with ammonia a t low temperatures (ammonia being a solvent for silver halide), is probably to effect a combined process of partial recrystallization and incipient reduction of the silver halide to colloidal silver, in such a way as to secure a suitable dispersion of colloid silver in the silver halide grain.” “The use of films in the air, up to the present, has been limited. The main development of aerial photography having taken place under war conditions, the exigencies of the Service were necessarily the first consideration. The introduction of the F-type camera, as already stated, provided the initial attempt to use the film in the British Air Service, but was far from successful. Under the conditions ruling, the average risk of failure could not be taken. For a time, attempts to use film had to be curtailed, but in 1918 there was again a tendency to revert to it. The film was not used to any great extent either by the Allies or their adversaries, although both sides tried hard to produce an efficient film camera. Not merely are there mechanical difficulties when using film cameras, but it cannot be said that there exists an emulsion on film base equal to that on glass. Whilst it is admitted that in the air the film has many advantages, these are quite outweighed by the many difficulties in handling material of this nature in development. Given the necessary time for research, both with regard to the emulsion and the methods of mechanically developing and drying, the film will eventually take its place in aerial photography.” p. 422. “Light filters, when used in conjunction with panchromatic plates for aerial photography, are not primarily intended for colour correction purposes; that the colours are corrected by their use is purely incidental. With many of the uses to which filters are put in other classes of photography we are not concerned here. When taking photographs from the air, the special problem which presents itself is to find the best method of eliminating the effects of

362

NEW BOOKS

haze on the photographic plate, without a t the same time unduly increasing the duration of the exposure. In taking photographs through this haze (or water vapour in suspension), on a panchromatic plate, without a filter, the results invariably lack clearness, contrast, and definition. The sole cause of this is the chemical action of the specially active ultra-violet, violet, and blue rays, which are scattered to a greater extent by the haze than rays which are chemically active. “All plates are more sensitive to the rays in the blue end of the spectrum. Therefore the effect on the plate is that the more active rays from the haze make a greater impression on the plate than the less active, i. e., the green, yellow and red. It must also be remembered that the only image which the blue rays are conveying is a veil of fog. Obviously, then, a means must be provided to restrain the action of the more chemically active rays, and allow the remainder to pass unchecked, thereby adjusting. as may be necessary, the actinic power of all the colors throughout the spectrum in their action on the plate,” p. 424. This is done by putting in a red filter or-speaking more accurately-a filter which cuts out a large portion of the blue. The reviewer did not know that “a modified form of flash-powder is recommended by MM. LumiBre and Seyewete, perchlorate of potassium being substituted for the usual perchlorate. The light produced is richer in actinic rays and the mixture is safer in use,” p. 448. I n the chapter on the technics of kinematography, p. 489, we read that “early cameras were quite simple compared with those now in general use. The modern camera will operate the film in the opposite direction by turning the handle backwards. This movement was a t first only used for making trick pictures in which all motions appeared in their reverse order when thrown on the screen, but it is now an indispensable item, and is used in conjunction with the fade mechanism and for double exposures. Counters which indicate the number of feet of film which has been exposed were in most cameras, but the cameras today have quite elaborate indicators by which an individual picture in the series can be brought opposite the lens if desired, no matter how many times the film may have been run through the mechanism or ‘reversed’. Double, triple, and sometimes quadruple exposures are made on the same film in the production of tricks, visions, and other effects. Another comparatively recent addition to the camera is the ‘fade’ mechanism. This, when set in action, causes one of the shutter discs to rotate slowly in relation to the other, so that the aperture in the shutter closes slowly till no light is admitted to the film. This has the effect of exposing each successive picture to a less extent till no light strikes the film. The effect known as a ‘fade out’ is thus produced. The opposite action-starting with the shutter closed-produces a ‘fade in’, and a combination of the two actions causes the appearance, now so much used, of one picture fading away and another taking its place, as in the well-known dissolving views.” “In the camera only one-half (generally somewhat less) of the movement of an object is recorded because the shutter obliterates the remainder of the movement. I n the case of a small object moving across the picture a t a high speed, no distinct rendering will be found on the developed negative. The distance moved during each exposure will be represented by a blur, the length of which will be equal to the amount of space passed through by the object in about 1/32 of a second. As the object moves while the shutter acts, the blur on the succeeding picture will be separated from the previous position by a blank space. When projected, a series of blurs, each separated by a space from the next one, will appear on the screen. A flying bird or a tennis ball is very inadequately reproduced. It might be supposed that so poor a record of the original could not give satisfaction, but as the eye views such a subject in nature it cannot distinguish detaile, nor can it hope to do so on the screen. As the eye follows the apparent movement of the object, the stronger part of the blurred imagesthe middle portions-impress themselves on the retina, and more or less remain and bridge over the spaces, and to an extent give the impression of continuity The longer the shutter remains open compared with its obliteration period, the longer in proportion will the blurs be and the shorter the spaces, and vice versa. It is doubtful whether any advantage would be gained by increasing the time of exposure to more than half. If the blurs could be made to join one another, owing to the persistence of vision, the appearance on the screen would be that of a blur more pronounced and longer in proportion.

NEW BOOKS

3 63

“In the first days, movements of persons and things were rendered on the screen in a jerky manner. This was greatly due to a false idea-a desire on the part of the photographer to secure sharp pictures. I n order to do this he reduced the opening of his shutter and recorded less than one-fourth of the total movement of the object. On projecting the picture, say of a moving ball so photographed, the appearance on the screen would not simulate the movement of one ball but present a string of balls, each one stationary, the first and last of the series faint, and the middle one well defined. The last of the series would disappear and others appear in front, each becoming stronger and fading in succession. With strong contrast perhaps six to eight images could be seen a t a time. iln image of a quick-moving limb appeared as if the owner was temporarily supplied with two or more, and the wheels of vehicles revolved in the wrong direction or not a t all, as often as not. “Animated pictures for a long time were much marred by flicker; the 16 per second flashes of light were painfully evident. Many devices were tried with the idea of curing the defect. It has been found that the eye cannot appreciate the intermittence of light and darkness, provided the changes take place a t a greater rate than about 40 per second. By putting two extra blades on the projector shutter 48 obliterations take place in one second, and to the eye the light appears quite continuous. One thing, however, is of great importance-the obliterations must be of equal length, and quite equally spaced; if not, a certain amount of flicker will be evident. The three-bladed shutter cuts off just about one-half the light, each blade being about one-sixth of a circle; the change of picture takes place in a little over I/IOO of a second, while one of the blades is passing. The loss of light is certainly great, and has to be made up by increase of electric power,” p. 500. Wilder D. Bancroft

Vat Colours. By Jocelyn F . Thorpe and C. K . Tngold. 22x14 cm; pp. xoi+Q91. London and N e w York: Longmans, Green and Co., 1925 Price: Sb.50. In the preface the author says: “Whatever the true nature of dyeing may be, whether, or no, It has a definite physical basis and involves some quantitative relationship between fibre and dye, it is certain that mere absorption, adsorption, or sorption of a dye base by the fibre, such as, for example, takes place when wool is coloured in a bath containing the hydrochloride of rosaniline, leads to an effect, which, from the point of view of fastness and stability, leaves much to be desired. “In reality the fibre is, in such circumstances, stained by the dye, and like all stained material will readily part with its stain. I n other words the dye is not fast and the fabric, therefore, unsuited to meet the conditions to which a dyed fabric usually has to be subjected. ‘[It has long been recognised that the only way in which fast colours can be imparted to fabrics is to cause the actual coloured compound to be formed within the fibre of the fabric, that is to say, by bringing about within the fibre the chemical reaction by which the dye is formed. There are, a t the present time, many ways known by which this can be done. For example, a large number of azo-dyestuffs can be diazotised on the fibre, and the diazonium salts thus produced can be made t o combine with other components thus leading to the production of new azo-dyes within the fibre. Many dyestuffs combine with metallic salts and can be stabilised on the fibre by after-treatment with these substances. Others form definite compounds with, for example, formaldehyde, and can be fixed on the fibre by the aid of this reagent. Again, the members of one of the most important and fastest series of colouring matters-the mordant colours-depend entirely for their value as colours on the property they possess of forming ‘lakes” with metallic hydroxides. “Still, the art of dyeing, which is certainly one of the most ancient of the arts, did not await the advent of the chemist but arose by trial and error. The ancient enquirer would find t o his hand many coloured substances and his desire would be to impart these colours to &her material, and possibly to himself, a t will. He would find that some served his purpose and that others did not. That some would impart colour, which, however faded rapidly or could be washed away, whilst others gave stable colours which survived all the weathering to which they were subjected. The colours he would find suitable were colours belonging to the vat series, and by using them he was discovering the process by which the

364

NEW BOOKS

fastest and most serviceable colours of the present day are imparted to the animal, vegctable, and artificial fibres. It is true that the ancient methods were hap-hazard and liable to give variable results; but the process by which, for example, the Hindu dyers used indigo was essentially the same as that by which the most modern colouring matter, say, duranthrene, is fixed pn the fibre a t the present day. For the vat dye is a substance insoluble in all: the usual solvents, but is rendered soluble by reduction and, in this form, is caused to enter the fibre from the dye-bath. Reoxidation by the oxygen of the air is then alone necessary t o reproduce the original colour within the fibre. “In the modern vat, reduction is achieved by chemical means under well-defined and well-understood conditions, but the ancient dyers found their reducing medium to hand within, for example, their ‘greening weed’, and it was only necessary to steep their fabrics in the mixture and then to expose them to the air. “Indigo, by far the most important and valuable colouring matter the world has known, was, up to the closing years of the last century, the sole representative of the vat series of colouring matters of commercial importance. The determinatiom of the constitution of this substance revealed the structure on which the property of vat dyeing was based, and the solution of the problem of its synthesis led, in the first instance, to the preparation of synthetic analogues of indigo having different shades of colour but similar properties. Later, the production of new types of compounds, notably from anthraquinone, placed the vat dyes in the fore-front of the synthetic colours and a t the present day they are the fastest, most brilliant, and most valuable of all the colouring matters.” The subject is treated under four heads: indigoid vat dyes; anthraquinone; miscellaneous vat dyes; preparations. The volume is chiefly straight organic chemistry and therefore of importance to the physical chemist of today mainly as a reference book. The chapter on Tyrian purple is interesting, however; though one wishes that the author had hazarded some guess as to the effect of sunlight in developing the color. The chapter on natural indigo is good and the reviewer was interested to learn, in the chapter on synthetic indigo, that vanadium oxide is superseding mercuric sulphate in the oxidation of naphthalene. “Until the beginning of the present century indigo remained the only known vat colour of any commercial value. The extreme fastness of indigo and of many of the colours produced by the vat process, towards light, and in the various vicissitudes which a dyed fabric may be called upon to undergo in daily use, naturally constituted a strong incentive towards research with a view to the production of other substances having similar properties. Researches with this object proceeded in three main directions. In the first place endeavours were made to prepare derivatives of indigo and in 1901 the first commercially valuable substance of this class, namely 5:7:5’:7’-tetrachloroindigo,was placed on the market by the Badische Anilin- and Soda-Fabrik. The second line of research had for its goal the production of analogues of indigo having a different carbon skeleton from indigo itself but a similar or a t any rate a strictly analogous chromophoric residue. The first signal success in this field was the production of thioindigo by P. Friedlander in 1906. The third main objective was the preparation of vat dyes similar t o incligo in the properties which render that substance of such great commercial value but possessing not only a different carbon skeleton but also an entirely different, chromophoric residue. The first two substances of this class to be prepared were indanthrene and flavanthrene, which were produced in 1901 by R. Bohn and placed on the market by the Badische Anilin. and Soda-Fabrik in the same year. ‘(A11vat colours must contain a reducible carbonyl group, and the reducible carbonyl groups in indanthrene and flavanthrene are the carbonyl groups present in an anthraquinone nucleus. In fact, indanthrene and flavanthrene may be regarded as the parents (in the historical sense) of the class of vat colours derived from anthraquinone, a class the membership of which is now so large that it may be said to constitute the most important series of colours a t present available. Almost every imaginable shade is represented. “In fastness the anthraquinone vat colours are in no way inferior to the indigoid colours, in fact many of them are faster than indigo itself. Considered as organic substances they are amongst the most stable known, indanthrene for example surviving a temperature of 470’ in the presence of air.

NEW BOOKS

365

“There is one noteworthy difference between vat colours of the indigo class and those derived from anthraquinone; for whilst the vats formed by reducing indigo analogues are either colourless or only slightly coloured, the reduction products of the anthraquinone dyes are themselves strongly coloured substances substantive to cotton in alkaline solution,” p. 173. The reviewer was also interested in the paragraph on p . 281. “Since indanthrene A is the commercially valuable constituent of crude indanthrene, it was an important discovery that either the A- or the B-compound could be made the principal product of the alkali fusion of 2-aminoanthraquinone by suitably regulating the experimental conditions. If the fusion be conducted a t 20oo-25o0 without the addition of any other substance the product consists of indanthrene A to the extent of about two-thirds and indanthrene B to the extent of one-third. In the presence of oxidising agents, however, for example, if a stream of oxygen be passed through the melt during the fusion process, or if potassium nitrate be added, only traces of indanthrene B are produced and indanthrene A is almost the sole constituent of the precipitate obtained during the subsequent oxidation of the aqueous solution. On the other hand, if the fusion be carried out below zoo’, and particularly if reducing agents are present then indanthrene B becomes the chief reaction product. This is the case, for example, when 2-aminoanthraquinone is heated a t 150” with very concentrated alcoholic potassium hydroxide.” Wilder D. Bancroft

Spectroscopy. B y E. C. C. Baly. Vol. I , Third edztion. 21 X 1 6 cm; pp. xz+298. London and New York: Longmans, Green and Co., 1924. Price: $5.00. The second edition was reviewed twelve years ago (17, 88). I n the preface of this edition the author says: “The

science of spectroscopy during recent years has advanced to a remarkable extent. Since the last edition was printed, new fields of investigation have been opened and the limits of knowledge in the older fields have been pushed very far forward. It has not been possible to comprise within one volume any account, however, brief, of the whole, and it has therefore been decided to divide the book into two volumes. The present volume deals with the standard methods of work in the infra-red, visible, and ultra-violet regions of the spectrum and thus includes the first half of the original volume.” This is now the standard book on the subject and there are many things in it of special interest. “During recent years the technique of manufacture of optical surfaces, both plane and curved, has improved in a most remarkable way. This very striking advance is in the main due to Michelson and his work on interferometers, since this work may be said to rest on the fundamental basis of truly plane surfaces. The necessity for such surfaces, indeed, became the mother of invention so that it is now possible to obtain optical surfaces, both plane and curved, with a n accuracy of figuring which would never have been obtained but for the pioneer work of Michelson. To a great extent this advance has been due to the English firm of Hilger and indeed Professor Michelson has stated that his measurements would have been impossible had it not been that this firm were able to produce interferometer plates of sufficient accuracy. This work has led to similar improvements in lenses and prism manufacture, and it is obvious that concurrently with such improvements an efficient system of testing the figuring of optical surfaces must be developed. Such a method has been worked out and is in use at the present time. It is not possible here to give a detailed description of the apparatus used, but the principle of the method consists in obtaining interference fringes with an interferometer of the Michelson type, one of the light beams passing through the surface under test. The interference bands give a contour map of the surface and from this map the nature of any imperfections can be recognized, that is to say, whether they are in the form of “hills‘[ or “valleys”. The treatment of the surface necessary for the removal of these can therefore be determined and a perfect surface obtained. The apparatus and method have been worked out by Twpman,” p. 95. “It must be remembered that all work of the highest accuracy demands the skill which can only be gained from understanding and experience. Understanding of the possible variations due t o the many sourcep of error, and experience which alone can teach the best method

366

NEW BOOKS

of reducing all these to a minimum. At the outset many will find keen disappointment their portion, and indeed a t times, as the late Lord Rayleigh said, one is tempted to doubt the constancy of Dame Nature herself. But there comes a t length to all who possess true love for her a great uplifting sense of victory ovei the many pitfalls with which she bestrews the way of the unwary. To such is born a very perfect happiness, the birthright of the true scientist who, without thought of personal gain, follows new paths, and, seeking inspiration at the fountain’s head, extends the confines of knowledge for the benefit of mankind,’’ p. 149. “The most recent results would seem to show that quite apart from its intrinsic interest investigation of the infra-red region holds out very great promise. At the present time the fascinating work based on the Bohr theory of the atom and the modern developments of X-ray spectroscopy have tended to focus the attention of scientific workers on to the most refrangible end of the spectrum, but I firmly believe that the time will soon come when the long-wave region will equal the short-wave region in interest. It has been shown that all substances possess powers of selectively absorbing infra-red rays to as far as X = 3000p, and.the integral relations between the many long-wave radiations selectively absorbed by a substance seem to prove that they are inherently characteristic of atoms and molecules. Up to the present no direct connection has been found between these very small frequencies and the very large frequencies dealt with in the Bohr theory. This connection will doubtless soon be discovered and I am brave enough to prophesy that the key to the problem of the absorption and radiation of energy by elementary atoms will be found in the infra-red. I t is hoped that more workers will enter this field and take a hand in unravelling the mysteries that still lie hidden therein,” p. 217. “The application of the focal isolation method has enabled Rubens and von Baeyer to discover the existence of waves of exceedingly long wave-length in the emission spectrum of quartz mercury lamps. They investigated the radiation from a large number of sources, including sparks between various metal electrodes and the arc between carbon electrodes. It was a t once found on trying with a quartz mercury lamp that there is present a very strong long-waved radiation, and it was soon discovered that this radiation must possess a n essentially different composition from that of the Welsbach mantle, the mean wave-length of which is 108p. For instance, a layer of quartz 14.6 mm. thick transmits 46.6 percent of the mercury lamp radiation and only 20 percent of the Welsbach mantle radiation. A number of experiments were carried out to test the transmitting power of various substances for these rays and for the rays from the Welsbach mantle. About seventeen different substances were experimented with, and in every single case the percentage transmission for the mercury lamp radiation was greater than for the Welsbach mantle radiation. Further, it was found that the percentage transmission was increased very materially if these radiations were previously passed through a 2 mm. layer of fused silica. It is evident, therefore, that the fused silica acts as a filter and cuts off some of the shorter wave-length radiation. Therefore, the percentage of transmission given by the same set of substances with the Welsbach radiation is very much smaller. Further experiments showed that the most effective ray filter is black cardboard, and the authors finally substituted for the silica a filter of black cardboard 0.38 mm. thick. I n order to determine the average wave-length of these radiations attempts were made to measure them by the quartz interferometer, as already described. The interferometer curves obtained with the quartz mercury lamp without any filter showed a very irregular character. Severtheless, it was evident that the main element of the radiation was about the same mean wave-length as that already dealt with from the Welsbach mantle. As soon as a 15 mm. layer of quartz was inserted a very considerable difference in the curve was noticed for the first minimum which previously was observed a t a thickness of the air film of about 26p now did not appear until the air layer was 42p thick. If the thickness of the quartz filter was increased to 42 mm. the first minimum was not observed until the air layer of the interferometer was 68p thick. At the same time the interferometer curve became more regular, and the faintly marked maximum began to make its appearance. \\7ith a filter of black cardboard 0.4 mm thick the periodic nature of the curve becomes more distinct. Here the minimum lies at a thickness of 7 8 . 4 and ~ ~ a strong maximum a t 1 5 6 . 9 ~ ~ but even in this case an accurate determination is still very difficult. Tt is evident, as is

NEW BOOKS

3 67

previously deduced from experiments on transmission, that the radiation after filteration through black cardboard contains a greater amount of the long-wave radiation. It is still doubtful whether the long-wave radiation consists of rays of different wave-length such as would be expected if they arose from the luminiferous radiation of mercury vapour, or whether it is simply a continuous thermal radiation. It is, however, safe to deduce from the observations that a large portion of this radiation possesses a mean wave-length of 314& or very nearly one-third of a millimetre. It may be added that Rubens and von Baeyer satisfied themselves that the radiation in question has its origin in the mercury vapour itself and not in the hot quartz walls of the lamp,” p. 236. “The investigation of infra-red absorption spectra received a great stimulus in 1912 when Bjerrum enunciated his conception of molecular rotation. The fundamental basis of this theory is that in addition to the characteristic frequencies in the infra-red established by its chemical nature a molecule will also possess a frequency in the long-wave infra-red established by its rotation. Bjerrum stated that the result of this will be that the characteristic frequencies in the short-wave region will not evidence themselves as single absorption lines but as groups of three frequencies, F R , F, F - R, where F is the frequency in the shortwave region and R is the rotational frequency. When as in actual practice a number of molecules are present there will be found a t F an absorption band containing the frequencies F nR, F, and F - nR, where n =: I , 2, 3, etc. Further, there will be found in the longwave region a series of absorption lines with the frequencies nR. From investigations made by Miss von Bahr in Rubens’s laboratory strong support was found for Bjerrum’s theory and since then further important results have been obtained on the structure of absorption bands,” P. 244. Wilder D. Bancrojt

+

+

+

The Constituents of Coal Tar. B y Percy EdwanSpzelmann. 2 2 x 1 4 cm; p p . xii g19 London and New York: Longmans, Green and Co., 1924. Price $4.25. “The object of this book is to be useful to those chemists who are interested in the individual constituent substances that together form coal tar. This material is so often looked upon as being the source mainly of a series of fractions valuable in commerce, that little thought i4 given to the large number of chemical entities that are present with the exception of perhaps a dozen individuals.” The subject is taken up under the general headings: coal tar; hydrocarbons; oxygen compounds; sulphur compounds; nitrogen compounds. The main part of the book is, of course, straight information of a very valuable nature. There are a number of minor points, however, which are of general interest. “All the benzene derivatives tested proved to be more toxic to insects, molecule for molecule, than carbon disulphide”, p. 9. “Bacterium aliphaticum and B. aliphatacum laquejaczens, both present in the earth, destroy the straight-chain hydrocarbons and leave the napthenes and aromatic hydrocarbons unattacked Others will destroy aromatic hydrocarbons preferably and even hydroxyl compounds,” pp. IO, 29. “The independent polymerisation of acetylene to form benzene is a change of fundamental theoretical importance. In practice, the conversion does not proceed far; but if activated wood charcoal is present, a whole series of products, from benzene to anthracene, result,” p. 16. “In all the work that has been done, in no case does naphthalene appear in a primary reaction. At a low temperature, the main products are paraffins, naphthenes, and olefines, the higher pure aromatic and hydrogenated hydrocarbons and phenols; and only above 750” does naphthalene begin to appear. It cannot be formed by hydrogenation of naphthenes and of hydrogenated aromatic hydrocarbons, so that it may result from the decomposition of substitutednaphthalene, though this is not likely. In fact, the mode of its production is not clear, unless it be supposed that the initial distillation of coal gives small ‘bricks’, such as acetylene, from which this substance can be built up,” p 19. “That ‘free carbon’ is not carbon is commonly known. but there are very few facts published about it. I t is the material left insoluble after pitch has been treated with hot benzene, though a better preparation is obtained by solution first in carbon bisulphide and finallyfin benzene When coumarone resin is destructively distilled and the pitch is extracted with

368

NEW BOOKS

solvents, the composition of the residue is probably closely similar to that of the free carbon of ordinary pitch,” p. 107. The reviewer is sceptical as to the existence of a phenol-water compound, CeHsOH.55H20, p. I 17. “The formation of red colour in phenol is due principally to the presence of quinone and catechol produced as impurities by oxidation, the colour itself being most probably due to phenoquinone, Cd&02(C&OH)2. Contributory evidence of this is found in the fact that an oxidizing substance has actually been detected in measurements of electromotive force of red phenol in alcoholic solution,” p. 119. The effect of carbon disulphide on the soil is remarkable. “After a temporary reduction of micro-organisms, there is an enormous increase, as well as an increase of soluble compounds of nitrogen and sulphur. I n its employment against undesired plant and soil life care must be taken lest the nitrifying bacteria of the soil be also killed. In sufficient quantity carbon disulphide will kill Azotobacter, but not all nitrifying bacteria are equally easily destroyed. Whilst its action varies towards different soils and crops, there is an undoubted improvement in sulphur crops, for instance, mustard,” p. 147. “It is remarkable, though the significance is not immediately apparent, that the majority of the nitrogen compounds in coal tar are nitrogen ring compounds and not substitution products of the aromatic series. This is contrary to what has been described among the oxygen compounds, where the phenols form an important proportion. They have not been fully worked out; there are still certain higher boiling alkyl derivatives that await identification,” p. 156. “Most remarkable is the fact that many substances, more particularly nitrogen compounds, dissolve to a much greater degree in a pyridine-water mixture than in either liquid separately, and a few, some sugars, for instance, in a smaller proportion. The matter is complicated by there existing a t least three solvents-pyridine, pyridine-water as a pyridonium compound, and water; together with the capacity of pyridine to form additive compounds,” p. 181. “Quinoline is an unusually good solvent for a large number of substances, behaving like pyridine in a complex manner, as the result of formation of additive compounds. In some cases a substance may be more soluble in an equimolecular mixture of quinoline and water Wilder D. Bancrojt than in each liquid separately,” p. 188. Physical Chemistry for Students of Medicine. B y Alexander Findlay. 3 2 x 1 6 cm; p p . ix+237. New York and London: Longmans, Green and Co., 1924. Price: $2.60. “The great advances which have been made in recent years through the application of the methods and teachings of physical chemistry to the study of physiology, bacteriology, and other branches of biological science underlying medical practice, have made it imperative for the student of medicine to acquire some knowledge of that branch of chemistry. In the present volume, those parts of physical chemistry which have found important applications in the medical sciences are discussed in an elementary manner, but also in sufficient detail to enable the student to read with profit larger and more specialized works. The treatment of the subject is based on the course of medical physical chemistry pursued by medical students in the Univeristy of Aberdeen, and regard is had throughout to the physiological and medical bearings on the subject. The chapters are entitled: the gas laws; the aqueous milieu of the life processes; diffussion and osmotic pressure; osmotic pressure in the living organism; the behaviour of electrolytes in solution; the law of mass action and chemical equilibrium; law of mass action applied to solutions of electrolytes; hydrion; velocity of reaction and catalysis-enzyme action; the colloidal state; adsorption; the permeability of the cell membrane. Any book by Findlay is sure to be good and this one is no exception to the rule. The last three chapters are entirely colloid chemistry. In the chapters on the colloidal state the subheads are: crystalloids and colloids: suspensoids and emulsoids; heterogeneity of colloid sols; the ultra-microscope; ultra-filtration; Brownian movement; osmotic pressure of colloid electrolytes and membrane equilibria; production of colloidal sols; electrical properties of colloids; mutual precipitation of colloids; precipitation of suspensoids by electrolytes; emulsoids; precipitation of emulsoids by electrolytes; protective action of emulsoids; formation of gels; imbibition. Wilder D. Bancroft