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NEW BOOKS LightandColour. By R . A . Hovstoun. 22x16 cm; p p . xi+l79. New York and London: Longmans, Green and Co., 1923. Price: 82.60. The publisher’s advertizement says that “this book is intended for the general reader and deals with the spectrum, the nature of light, colour photography, and allied subjects. The treatment, though popular, is everywhere from the most modern standpoint.” This statement is unnecessarily modest for the book can be read with profit by any scientific man. My attention was first called to the book by Professor Eve of McGill University, who told me that he had enjoyed it,. I am glad to bear witness that I have b0t.h enjoyed and profited by it. The chapters are entitled: Newton and the colours of the spectrum; the nature of light; invisible rays; applications to the structure of atoms and stars; t,hc primary colours; colour blindness; colour photography and stereoscopy; t>helight of t.he futiire; photochemistry and allied effects; photot,herapy; the psychology of colour. There is a distinctly interesting diagram of the rainbow, p. 5. and it is certainly worth while to quote the views on color of Dr. Barrows, who was Newton’s predecessor in t,he Lucasian professorship of mathematics. “White is that which discharges a copious light equally clear in every direction. Black is that which does not emit, light a t all, or which does it very sparingly. Red is that which emits a light, more clear than usual, but interrupted by shady interstices. Blue is that which discharges a rarefied light,, as in bodies which consist of white and black particles arranged alternately. Green is nearly allied to blue. Yellow is a mixture of much white and a little red; and purple consists of a great deal of blue mixed with a small port’ion of red. The blue colour of the sea arises from the whiteness of the salt it contains, mixed with the blackness of t,he pure water in which the salt is dissolved; and t.he blueness of the shadows of bodies, seen at the same t,ime by candle and daylight, arises from the whiteness of the paper mixed with the faint light or blackness of twilight. ” Houstoun adopts the view of Edridge-Green in regard to the presence of indigo in the spectrum. “Dr. Edridge-Green states that Newton had exceptionally good colour vision, and that he saw a difference in t’hespectrum at this point which was not visible to the average man. According to Edridge-Green’s classification of colour vision the average man sees only six colours in the spectrum, red, orange, yellow, green, blue, and violet. He consequently refers t,o normal colour vision as hexachromic. . . . The average man sees, of course, int,ermediate shades between these colours, but these six colours appear to be fundamental. But there are certain individuals, the seven-colour class or hepta-chromic according to Edridge’s-Green’s terminology, who see a seventh colour, indigo, between the blue and the violet. They have a decidedly better colour perception than the hexachromic. It is not merely n matter of colour nomenclature; the heptachromic really see something a t this region in the spectrum, which the hexachromic do not see. Newton, arcording to EdridgeGreen, was a hept.achromic.” Edridge-Green, states that only about four in a t)housand have heptachroinic vision; but Houst,oun found three cases out of eighteen observers t>akena t random, p. 9. These three all objected to the word indigo, and chose dark blue as a more suitable name; they all said i t was more like blue than violet,. They placed the boundary between blue and indigo at 4 6 5 ~ ~Another, . and perhaps the real, reason why Newton included indigo was because this made seven colors and brought his phenomenon in line with the doctrine of the mllsic of the spheres, p. 1 7 , according t,o which the sun and moon and t,he five planets, Bat,urn, Jupiter, Venus, Mars, and hlercury, emitted musical notes as t,hey revolved in their orbits, thereby producing a heavenly harmony. “The music of the spheres forms a curious bypath in the history of human thought. And yet not altogether a bypath, for it inspired Kepler t,o discover the third law of planetary motion, and upon this law Bewton built his theory of gravi tat ion. ”

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“It will be not,iced in the above scheme that the sun and moon arc included in the number of t.he planets. This was the teaching of the priest.-astronomers of the early Bahylonian civilisation. TJranus and Neptune were, of course, not discovered then. The seven planets were regarded as gods, an idea that lingered on into medieval t.imes in astrology; the sun’s influence on the crops and weather was, of course, very obvious, and it became natural to assume that the other planets exerted an influence on human affairs, less obvious perhaps, but nevertheless very important. To a primitive pastoral people, often abroad at night under a clear tropical sky, the planets would nat.urally appear very mysterious moving on their regular paths among the stars. The division of the month into weeks was instituted in their honour, an arrangement still in use in this country with the names of the Scandinaviandeitiessubstitut.ed. I t was doubtless owing to there being seven planets, that the number seven acquired the sacred charrtct,er it has in the Bible, that there were seven important metals in nlchemy, that there were seven notes in the octave, and seven colours in the spectrum,” p. 19. “On p. 71 there is 3 discussion of the effects of mixing coloured lights. “The retl required for our experiment must be a pure red without any tint of orange, somewhat similar to the red of the railway signal lamps; the green must contain neither yellow nor blue, and must be purer than the green of thc signal lamps; the blue must be an ultramarine with a good deal of violet in it. Under these circumstances if the red is superimposed on the green we obtain yellow. Strong red imposed on weak green gives orange, weak retl on strong green yellowish green. Green superimposed on blue gives peacock blue. Red supcrimposed on blue gives magenta, nnd red on H stronger Idue gives pinple. Red, green, and blue superimposed cn one mother make whit.!. If white is dimmed, wc get, gray; if orange is dimmed we get brown. Supcrimposipg white on any rolour makes it. paler. Thus by means of the thrw colours, red, green, and blue, we ohtnin nearly all the rolowa that occur in nnturc. They do not give us violet, hut pure violet does not occur frequently i n nature. So red, green, and blue are termed the primary colours. . . . “Peacock hlue, magenta, and yellow are termed the three complementaries, since each of them combined with one of the primaries gives white. Peacock blue is sometimes referred to as minus red, sinre it is the coloiir obtained by subtracting red from white, and in the same way magenta and yellow w c referred to R P minus-green and minus-blue.”’ “So far we have dealt with adding or mixing coloured lights. Lye have now to consider t,he mixture of coloured pigments. This is a subject with which t o a certain extent wc are all familiar, owing to our experience with water rolour paint-boxes when children. We then learned that approximate representations of all colours could be produced by mixing red, yellow, and blue, or more accurately, crimson, yellow, and peacock blue, i . e . the three complementaries on the colour diagram. For crimson and yellow mixed in varying proportions gave red and orange, yellow and blue gave green, and blue and crimson mixed in varying proportions ultramarine-blue and the purples. Hence these colours have been termed by the artists the primary or elementary colours, for human nature has had a natural tendency to think in terms of elements, especially in medieval times; some painters have restricted themselves to the use of these three colours, adding black for the purpose of darkening them and obtaining the browns and greys, although they would undoubtedly have obtained a better representation of the hues of nature, if they had used other colours as well. “If we desire to renew our studies in mixing coloured pigments, then we can go back to the crimson lake, gamboge, and Prussian blue of the water colour paint-boxes. Or we may use instead Arnold’s waterproof inks, carmine, yellow, and Prussian blue, which give morr intense colours. If we wish to exhibit the mixing of pigments to a large audience, the best method is to get six glass cylinders, fill the first with a crimson liquid, the second with n yellow liquid, and the third with a blue liquid, and then pour the liquids together into the fourth, fifth, and sixth to make orange, green, and purple. The glasses should be held before a well-lighted white hackground. Fuchsin, naphthol yellow, and copper sulphate are suit,able colours to use.

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“If we add yellow and blue pigments we get green. If wc add yellow and blue lights we get white. Whence comes the contradiction? ‘[A yellow pigment appears yellow because, when the constituents of white light fall upon it, the blue and violet are absorbed, and red, yellow, and green reflected. Most yellows occurring in nature are not very pure, and reflect red and green as well as yellow. A blue pigment appears blue because it absorbs red and yellow, most blues occurring in nature are not very pure, and reflect green as well as blue. When the yellow and hlue pigments are mixed, the mixture absorbs all the colours absorbed by its components singly, Le., blue, violet, red, and yellow. Green is the only colour left. I t alone is reflected and the mixture appears green. A mixture of pigments gives only the colour which neither absorbs, not the sum of the two colours, as we obtain when adding lights,” p. 75. “Dalton was first distinctly convinced of his peculiarity of vision in 1792,when lie was 26 years of age, by the discovery that the flower of a geranium which appeared to others pink in all lights, appeared to him blue by day, and what he called red by candle light. All his friends except his brother said there was not any striking difference in the colour by the two lights. This observation led him to examine t,he peculiarities of his vision; lie then found that the pure colours, red, orange, yellow, and green were practically all alike to him, and that he called them all yellow, but that he coiild distinguish blue and purple, and that he called these colours by the correct names. Dalton said that blood appeared bottle-green to him, grass a,ppeared very little different from red. A laurel leaf WRS a good match for a stick of sealing wax,” p. 87. “Put in it,s simplest form the Young-Helmholtz theory states that in the ret,ina of each eye there end three sets of nerves, one set for the sensation of red, another for t>he sensation of green, and a third for the sensation of blue. When red light falls on the eye, it stimulates the red nerves. When yellow light falls on the eye, it stimulates both the red and green nerves. When white light falls on the eye, it stimulates all three sets of nerves. The colour blind lack either one or two sets of nerves. If they lack two, they arc totally colour blind, and are referred to as monochromats. If they lack one set, they are referred t,o as dichromats; all the commonly occurring cases are dichromats who lack either the red or green set of nerves, and are consequently referred to as red or green blind. Observers with normal colour vision are referred to as trichromats. “One objection to the Young-Helmholtz theory is that there is no anatomical evidence for the three sets of nerves, but’ the most serious objection is, that the colour blind do not fit into the original classification. I have tested carefully some thirty colour blind individuals, and not one of these agreed with Helmholtz’s typical cases. Helmholtz became aware of t,he inadequacy of his earlier views, and before his death he modified his theory so as to make it better able to take account of the cases occurring in practice. But when the theory is modified, it loses its original simplicity and force. “The other theory most prominently before the public a t present is the non-elemental theory which has been advocated by Dr. Edridge-Green for the past twenty years. According to this theory there are no elementary sensations; colour vision occurs in all degrees of goodness passing in insensible gradations from the tot,ally colour blind through the normal to those who have better colour vision than the normal, and the colour blind should not fall into classes like the red-blind and greenblind. “It should be stated that the mathematical development of Helmholtz’s modified theory does equally well for the non-elementary theory, so that there is no serious difference between the two standpoints; the current practice of identifying Helmholtz’s name with his earlier view is hardly fair to his memory, in consideration of the great advances he made in the study of the subject,” p. go. “The bead test reveals not only colour blindness, but differences in the classification of colours. Some people are very particular, and put only a pure red in the red hole; others include pink and crimson under red, and a few are inclined to extend the term to include brown and amber. Usually out of four men two put peacock blue in blue and one puts it in green, while the fourth leaves it in the drawer. Three out of four women put

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peacock blue in blue. Such differences interest the people using the test very much; in fact I have heard the apparatus called “The Parlour Game Test for Colour Vision.” and it is really more int,eresting than many parlour games. In using it the examiner must distinguish between a selection made because the examinee sees the colours different and a selection made because he classifies them differently; this is, however, easy,” p. 93. “The best known name in the region of phototherapy is that of Professor Finsen of Copenhagen, who worked for many years on the subject, from 1893 onwards. He had an institute for phototherapy a t which he treated large numbers of patients; he was fortunate in obtaining help both from private individuals and the state, and in thus being able to carry his plans to completion. He was awarded a Nobel Prize for his work. His chief success was with the skin disease lupus, a form of tuberculosis, of which he treated from 1,200 to 1,300 cases. It is stated that he obtained a cure or considerable improvement in between 90 and 94 per cent. of these cases. But his treatment is not much used in our own country at prcsent, apparentlv because it is slow, tedious, and expensive,” p.148. “There have been two schools of thought with reference to rickets. According to the one view the disease ia due to a deficiency of a vitamin-the fat soluble vitamin A-which promotes growth. Vitamins are substances wit,hout the presence of a very small quantity of which the body is unable to derive the proper nourishment from its food. According to the other view the disease is due to confinement and defective hygiene. The two views are probably complementary, not contrndict.ory. In many cases a course of cod-liver oil has been very successful, apparently because it supplied the lacking vitamin. “It has been suggested that sunlight or ultra-violet; light sets up inflammatory processes in the skin which produce vitamin A by a photochemical reaction. Thie would account for the seasonal prevalence of rickets in winter and early spring. The matter is, however, still very hypotheticd,” p. I 50. “Thus the mountain sunshine has a quality which the sunshine of the valleys and plains has not; it contains certain ultra-violet radiations which the latter lacks. At first sight I O or 20 A. 1’. may not seem worth climbing the mountain for. But the fact that there are more of the limiting radiations at high altitudes means that more are being absorbed there; now the absorption of ultra-violet light is often accompanied by ionisation-Le., in this case by change in the electrical conditions of the atmosphere. This may make the air fresher. What exactly constitutes fresh air is not known. It is not merely sufficient to diminish the carbon dioxide content, ns was formerly thought to be the case. Everyone admits that thousands of cubic feet, of air may be pumped through a room and yet leave it with a close feeling. There are subtle changes in the condition of the molecules that defy chemical analysis, and yet conduce very much to our feeling of health. Possibly the radiations present in mountnin sunshine and absent from ordi.nary sunshine may bring these changes about,” p. I 52. In regard to the Cooper Hewitt lamp the author says, p. I 54, that “the colour of the lamp was always against it; it gave everything a green, ghastly hue. Golden hair appeared a mossy green, a penny stamp was exactly the colour of R three half-penny one when illuminated by its rays, and I was told by some acquaintances, who worked temporarily during t.he war on the night shift in a factory illuminnt,ed by the mercury arc, that, the first night they opened out their sandwiches, t,hey simply looked at them in the green light, and then tied them up again; t.he colour was too much for them.” Wilder D . Bancroft Dimensional Analysis. By P . TI’. Rridgman. R S X 1 6 c m ; p p . 115. New Hacev: Yale Unisersify Press, 1922. Price: $5.00. “The growing use of the methods of dimensional analysis in technical physics, as well as the importance of the method in theoretical investigations, makes it desirable that every physicist should have this method of analysis at his command. There is, however, nowhere a systematic exposition of the principles of the method. Perhaps the reason for this lack is the feeling that the subject is so simple that any formal presentation is superfluous. There do, nevertheless, exist important misconceptions

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to the fundament,alcharacter of the method and the details of its use. These misconceptions are so wide-spread, and have so profoundly influenced the character of many speculations, as I shall try to show by many il1ust)rativeexamples, t,hat, I have thought an attempt, to remove the misconceptions well worth the effort.

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“1 have therefore attempted a systematic exposition of the principles underlying the met,hod of dimensional analysis, and havc illustrated the applicat’ions with many examples esper,iallg chosen t o emphasilre the points concerning which there is the most common misunderstanding, such as the nature of a dimensional formula, the propel number of fundamental units, and the nature of dimrnsional constants. In addit,ion to phe examples in the text, I have included at the end a number of practice problems, which hope will be found instructive.” Dimensional analysis and the principle of similitude are interchangeable terms, p’ I O . “The purpose of dimensional analysis is to give certain information about the relations which hold .hetween the measurable quant.ities associated with various phenomena. The advantage of the method is that it is rapid; it enables us to dispense with making a complete analysis of the situat,ion such as would be involved in writing down the equations of motion of a mechanical system, for example, but on t.he ot,her hand it does not give as complete information as might be obt.a.ined by carrying through a detailed analysis,” p. 17.

“The tlimensional formula. need not, even suggest rerhin esseptial aspects of the rules of operat.ion. For example: in the dimensional formula of force as mass times acceleration, t.he fact is not, suggested that force and arceleration are vect.ors, qnd the components of each in the same direct.ion must be compared. Furthermore, in o i r measurements of nature, the rules of operation are in our control to modify as we see fit, and we would certainly be foolish if we did not, modify them to our advantage according to the particular kind of physical syst,em or problem wit,h which we are dealing. We shall in the following find many problems in which there is an advantage in choosing our system of measurement, that is, our rules of operation, in a particular way for the particular problem. Different systems of measurerncnt may differ as t o the kinds of quantity which we find it convenient to regard as fundamental and in terms of which we define the others, or they may even differ in the number of quantities which we choose as fundamental. All will depend on the particular problem, and it is our business to choose t,he spstcm in the way best adapted to the problem ill hand. “There is therefore no meaning in saying ‘the’ dimensions of a physical quantity, until we have also specified the system of measurement with respect to which the dimensions are determined. This is not always kept clearly in mind even by those who in other conditions recognize the relative nature of a dimensional formula,” p. 24. The author holds that i t is permissible, for instance, to make the dimensions of the temperature the dimensions of cnergy if t,hat is compatible with the physical f a d s (and it seems to he) and if t.hat, seems arlvant ageous. “This view of the nature of a dimensional formula is directly opposed to one which is commonly held, and frequently expressed. It is by many considered that a dimensional formula has some esot.eric significance connected with the ‘ultimate nature’ of an object, and that we are in some way getting at, the iiltimate nature of things in writing their dimensional formulafi. Such a point of view sees something absolute in a dimensional formula and attaches a meaning to such phrases as ‘really’ independent, as in Riabouehinsky’s comments on Lord Rayleigh’s analysis of a certain prohlem in heat transfer. For t,his point of view it becomes importa.nt t,o find the ‘true’ dimensions, and when the ‘true’ dimensions are found, it.is expected that something new will he suggested about the physical properties of the system. To this view it is repugnant that there should be two dimensional formulas for the same physical quantity. Often a reconciliation is sought by t8heintroduction of socalled suppressed dimensions. Such speculations have been particularly fashionable with regard to the nature of the ether, but so far as I know, no physical discovery has ever followcd such speculations; we should not expect there would if the view above is correct,” p. 24.

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“My point of view is essentially that precisely the same experience which is demanded to enable us to say whether a system is mechanical or electrical is the experience which is demanded in order to enable us to make a dimensional analysis. This experience will in the first place inform us what physical variables to include in our list, and will in the second place tell 11swhat dimensional constants are demanded in any particular problem,” p. jo. “With regard to the dimensional formulas of dimensional constants, we may merely appeal to experience with the observation that all such constants are of the form of products of powers of the fundamental quantities. But it is evident on reflection, that any law of nature can be expressed in a form in which the dimensional formulas of the constants are of this type, by the device, already adopted, of introducing dimensional constants as factors with the measured quantities in such a way as to make the equation complete. We will therefore assume that the equat>ionsof motion (which are merely expressions of t.he laws of nature governing phenomena) are thrown into such a form that the dimensional constants are of this type; this is seen to involve no real restriction. It appears, therefore, that dimensional analysis i s essentially of the nnture of a n analysis of a n analysis,” p. 52. “We are to imagine ourselves as writing out the equations of motion at least in sufficient det>ailto be able to enumerat,c the elements which enter them. It is not necessary to actiially write down the equations, still less to solve them. Dimensional analysis then gives certain information about the necessary character of the results. I t is here of course that the advantage of the method lies, for the results are applicable to systems so complicated that i t would not be possible to write the equations of motion in detail,” p. jz. “There are in engineering practice a large number of problems so complicated that the exact solution is not obtainable. Under these conditions dimensional analysis enables us to obtain certain informa.tion about the form of the result which could be obtained in practice only by experiments witahan impossibly wide variation of the unknown arguments of the unknown function. In order to apply dimensional analysis we merely have to know what, kind of a physical syst,em it is we are dealing with, and what the variables are which enter the equation; we do not even have t.0 write the equations down explicitly, much less solve them. In many rases of this sort, the partial information given by dimensional analysis may bo combined with nieasurement on only a part of the totality of phpAica1 systems covered by the analysis, so that together all the information needed is obtained with much less trouble and expense than would otherwise be possible,” p. 81. “Tho methods of dimensional analysis are worthy of playing a much more important part as a. tool in theoretical investigat.ion than has hitherto been realized. No investigator should allow himself to proceed to the detailed solut,ion of a problem until he has made a dimensional analysis of the nature of the solution rvhirh will he obtained, and convinced himself by apped to experiment ihnt the points of view embodied in the underlying equations are soiind,’.’ p. 88. Wilder D. Bancroft

Atoms. Bp Jean Perrin. Translated By D. L1. Hamtnick. Srcond English edilion. N e w York: I). l‘an Nostrand Co., 1923. Price: $2.60. The second English edition is based on the revised form of the eleventh French edition. The first Frcnch edition was reviewed eleven years ago (17, 563) and the first German one ten years ago (18, 451). In this edition the chapters are entitled: chemistry and the atomic theory, molecular agitation; the Brownian movement-emulsions; the laws of the Brownian movement; fluctuations; light and quanta; the atom of electricity; the genesis and destruction of atoms. “At very low temperatures peculiarities, at first sight hard to explain, are observed with gases as well as with solids. Even at the temperature of melting ice (273” absolute) the sperific heat of hydrogen is only 4.75, and is thus distinctly lower than the theoretical value 4.97. The discrepancy is not great, but, as Nernst has justly pointed out, it lies in the direction absolutely irreconcilable with Boltsmann’s results on rotational energy. Under his direction investigations have been carried out by Eucken at a veiy low temperature, and 2 2 x 1 5 a n ; p p . xii$251.

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have led to the surprising result that, below 50” absolute, t.he specific heat of hydrogen becomes 3, as with the monatomic gases! For other gases the specific heat at low temperatures also falls below the theoretical value (t.hough at much lomcr temperatures than hydrogen), and in fact it seems probable that a t sufficient,ly low temperatures all gases have t.he same specific heat as the monatomic gases, namely 3 ; t,hat is to say, the molecules, although not spherical, no longer by their impacts impart to each other rotational energy comparable wit.h t,heir energy of translation,” p. 7.3. “tn short, each molecule of the air we breathe is moving with the ve1ocit.g of a rifle bullet; t,ravels in a straight line between two impacts for a distance of nearly one ten-thousandth of a millimetre; is deflected from its course ~,ooo,ooo,ooo times per second, and would be able, if stopped, to raise a particle of dust just visible under the microscope by its own height. There are thirty milliard milliard molecules in a cubic centimetre of air, under normal conditions. Threc thousand million of them placed side by side in a straight line would be required to make up one millimetre. Twenty thousand million must he gathered together t o make up one thousand millionth of a milligramme,” p. 82. “The objective reality of the molecules becomes hard to deny. A t the same time, molceular movement has not been made visil)le. The Brownian movement is a faithful reflection of it, or, l)et,ter,it is a molecnlar movement in itself, in the same sense that the infra-red is still light. From the point of view of agitation, t.here is no distinction hetween nitrogen molecides and the visible molecules realised in the grain of an emulsion, which have a gramme molecule of the order of IOOOOO tons. Of course such grains are not chemical molecules, in which all the cohesive forces are of the nature of those uniting the carbon to the four hydrogen atoms in methane”, p. 105. “If we could examine a solid body with a miwoscope magnifying 3x1010 times the body would appear to us t n be composed of extremely dense granules about t.wo millimeters in diameter with a mean clistance of about twent,g mcters between them. . . Matter is porous and discontinuous to an extent far beyond our expectation,’’ p. 161. “In this connection I should like to add a remark with reference to the strength of the the dumb-bell-like hydrogen molecule i s spinning valency b o d . When a t ahout ZOOOT, without rupture perpendicularly to its axis with a frequency but little IPSS than a hundred thousand milliards of revolutions per second, it is obvious that the bond or union between the atoms must be resisting the centrifugal force. A union that would give the same st.rength to a dumb-hell would have a tenacity a t 1emt 1,000t,imes that of fiteel,” p. 163. “It seems to me ‘that, for any given molecule, the probable vahie for the time that must elapse before, undcr the sole influence of impacts, a certain ,fragile condition will be rrached must be smaller the more often the molecule receives impacts per second. Further, supposing this fragile stat,e to have been reached, the probable value for the time required for a molecule to receive the kind of impact capahle of rupturing it must again he shorter the more frequent the impacts. For this doiilde reason, if rupture is to he produced by molecular impart, it should occur more frequently (and dissoriation should therefore becomc more rapid) as the concentration of the gas increases. “Since this is not the case, dissociation cannot be caused by impact. hJolecules do not t!ecompose by striking against each other, and we may say: T h e probabilily that a n y niolecule will be riiptwed does not depend upon the nunibw of impacts it receives. “Sinre, however, the rate of dissociation depends largely on the temperatnre, i+e arc rcminded that tempernture exerts its influence by radiation as well as through molecular inipact, and are facod with the suggestion that the cause of dissociation lies in the visible and invisible light that fills, under stationary conditions, the isothermal enclosure wherein thn molecules of the gases under considerations are moving. ?‘he essentinl mecha?tisin of nll cherniral reaction i s therefore to be soicyht in the aclion of light upon atoms,” p. 164. Wilder D. Bancroft The Fundamental Processes of Dye Chemistry. By H . E. Pierz-David. Translaled by F.-4. Mason. 2 4 X 1 6 c m ; p p . x i v f d 4 0 . N e w York: D. V a n Nostrand Company, 1981. Price: $6.00.

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“The manufacture of synthetic colours has attained to such importance that it seems desirable to familiarize the rising generation of chemical technologists with the methods of production of the more important interniediates. With this cnd in view, I have attempted a description of these methods in a manner which may be helpful even to those unfamiliar with technical opers.tions. “AZOcolours form the largest sect>ionof artificial dyes, and in consequence most attention has been devoted to the prepa.rat’ionof the necessary intermediat,es. As, however, many of these intermediates are also used in t,he synt,hesis of other classes of dyes, such as Indigo, ilzines, Thiazines, Aniline Black, Sulphur colours, and Triphenyl-methane dyes, it may fairly be claimed that the field of Synthetic colours in its essential features is covered by the present volume. ‘ T o complete t8hepict.ure I have added recipes for a few dyes and included some general observations on the technique of dye manufacture. With only trifling exceptions the dyes dealt with can all be obtained from the intermediates described in the first portion, so that the st,udent is enabled to obtain a clear view of the stages of development of a dye.” “It has further been found that the manufacture of the intermediate product,s is far more difficult than tha,t of the finished colouring matters, and, in addition, the apparatus, and machinery needed for the intermediates occupies a far greater space than that required for the actual dyes. The Anthraquinone dyes, however, form an exception to this generalization. With the exception of this last case it may be said that, the ratio of the size of the installations and the number of workmen required for intermediates and dyes respectively is approximately as 3:1, or, in other words, a colour factory whirh has previously purchased its intermediates and now intends to make them itself must enlarge itself about fourfold.” The chapters are entitled: sulphonations; nitrations and reductions; chlorinations; oxidations; condensations; azo dyes; triphenylmethane dyes; sulphur melts; miscellaneous dyes; summary of the most important methods; vacuum distillations in the lahoratory and in the works; notes upon the construction and use of autoclaves; structural materials used in dye chemistry; technical notes on works management; example of costing of a simple dye; analytical details. In several places, pp. 17, 55, 57, stress is laid upon the importance of etching the iron before starting reduction with iron and acet,ic acid. One wonders whether this is an indirect way of getting a litt,le ferrous salt into solution. The layman is start.led to read, p. 55, that “dinitrobenzene is an extremely poisonous substance and quite as dangerous as prussic acid. The workmen who deal with it must always change their clothes and wear gas masks. The substance can even penetrate through the skin into the blood and causes acute cyanosis, a form of poisoning in which the lips of thc patient become blue, the pulse weakens, and frequent,ly death supervenes after long illness.” “On the works scale the introduction of chlorine and bromine into aromat,ic hydrocarbons is carried out almost exclusively by direct halogenat)ion. . . . Benzene readily takes up chlorine in the presence of carriers; iron is the only catalyst of practical importance. In this case the best iron for the purpose is not cast iron but wrought iron, as it acts less vigorously,” p. 83. “Recently at.tempts have been made to facilitate the introduction of chlorine into the side chain by the use of ultra-violet rays from a Uviol lamp. This only succeeds, however, when there is no trace of iron in the reaction mixture. Even the minute traces of iron in the quartz lamp, or in the porcelain vessels, or the dust of the factory containing iron rust, may cause serious disturbances,” p. 93. Wilder D.Bancroft L’Bvolution universelle. By Branislav Petronie~ics. 21 X 13 em; p p . viii4-212. Paris; Filix Alcan, 1991. Price: 7 . S O francs. In the preface the author says that “although written by a metaphJ-sicist, this book is intended as much for the ordinary readers and the scientific men as for the metaphysicist. The ordinary reader will find a clear statement of the chief facts of universal evolution; the scientific man will find a careful discus-

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sion of tho truth of thrsc facts; while the metaphysicist will find n severe criticism of this discussion.” The subject is presented under three heads: the general bases of evolution; inorganic cvolution; organic evolution. In the last chapter on the laws of organic evolut.ion there are given nearly sixt,)-laws, which seems a liberal allowance. The author considers that there are four main hypotheses in regard to the origin of the world and all that in it is. “The first is the hypothesis of the eternity of t,hings, according to which the inorganic world is eternal and the organic species are et.ernal and immutable. The metaphysicd systems of Aristotle and Spinoza are typical representatives of this hypothesis. The second is the hypothesis of creation according to which the inorganic world and all living forms were created by God; but,, once created, have remained immutable. This is the orthodox hypothesis of the Church, and the nat.uralists Cuvier and Agassiz are the best known upholders of this view. The third hypothesis is that, of gener@ined spontaneous generation, arcording to which the inorganic world is the product of the transformation of pure thought and living forms are the product of an immediate transformation of inorganic matter. The doctrine of Buddha is the only representative of this hypothesis for the inorganic world while many Greek philosophers-.4naximander, Empedocles, Epicurus--teach the spontaneous generation of all living forms regardless of their complexity. Thr fourth hypothesis is that of evolut,ion, according to which the inorganic world as it now exists has developed from an original state quite different from the present, one, while the living forms have arisen through the transformation of lower into higher forms. Among the scientific men Laplace is the best, known protagonist of evolution in the inorganic world; while Lamarck and Darwin occupy a similar position with reference to organic evolution. Among the philosophers the outstanding figures are Kant for the inorganic world and Spencer, Hartmann, and Bergson for the organic world. It’z’lder D. Bancroft

Van Nostrand’s Chemical Annual for 1922. Edited bv J . C‘. Olsen. Fifth edition. New York: D. Van Nostrand Company. 1992. Price: 84.00. ‘ributedchiefly to the heat generated thereby, p. 2 1 . Wohler attributes the specific action of detonators chiefly to the high pressures produced, p. 23. The effect of a heated wire in igniting explosive mixtures of fire damp is complicat#ed l q r catalytic action, a copper wire being less effective than n platinum one and more effective than an iron one, p. 41. No experiments seem to have been made on any poisoning action by carhon monoxide. The explosion flame, p. 109, may be composed of a primary flame due t80the explosion and a secondary one due to the burning of combustion material scattered by the explosion. Black powder gives a long primary flamc and ammonium nitrate a short one. Picric acid gives a short primary flame and a large secondary one. By adding salt to picric acid the secondary flarrc can be eliminated, though there is an increase in the primary flame, p. 113. For mines where there is much fire damp, only those explosives should be used which give a short primnrv and no secondary flamc. There is an interesting account, p. 143, of the development of black powder, which the aut,hor considers as an outgrowth from Greek fire through the fireworks stage. For six hundred years black powder was the only propellant and thc gelatinized, smokeless powders do not run back fifty years. In 1882 Reid and Johnson made a partially gelatinized nitrocellulose powder for sporting purposes and in 1884 von Duttenhofer made the first gelatinized powder for military uses, p. 145. It is claimed that lightning will only set the gelatinized powders on fire and will not cause them to explode, p. 148. Nitrogelatine consists of nitroglycerine converted into a solid jelly by the addition of small amounts of a special colloid wool which is peptized by nitroglycerine, though the word peptization does not occur in the book and the author evidently believes that in most cases we are dealing with true solutions a t some stage. Cheddite consists usually, p. 183, of 79% potassium chlorate, I % nitronaphthalene, 15% dinitrotoluene, and 5% castor oil. The nitrocompounds are first dissolved in the oil by warming and the finely powdered chlorate is mixed intimately with the still warm solution. Permonite is a mixture of potassium perchlorate, ammonium nitrate, sodium nitrate, trinitrotoluene, flour and sawdust, gelatinized with glue and glycerine. A good explosive is obtained when liquid air, enriched to ninety percent oxygen, is taken up by cork charcoal and some petroleum paraffin, or naphthalene is added, p. 187. “Fresh liquid-air cart,ridges are characterized by a power of action second to none. This high explosive power does not last .long and after fifteen to thirty minutes the liquid air evaporates from the cartridge and then there is no explosive left.” When breaking ice in the Rhone river, it was not sufficient to cut grooves in the ice a meter long and 4.5 cm. deep and t o fill those with dynamite. The explosion gave rise t o long cracks but did not shatter the ice, p. 189. “Vertical holes, 8-10 cm in diameter, were bored in the ice and dynamite cartridges containing 17-30 grams of explosive were stuck through the holes to points about 70 cm below the surface of the ice. Working in this way i t was easily possible to shatter R surface of fifty thousand square meters of ice per day.” The beneficial effect of legislative restrictions in regard to storage and handling of explosives is seen clearly in England where the percentage of workmen injured dropped in twenty years from four to one although the numher of workmen rose from two thousand to six thousand, p. 190. Tt‘iilder D.Rnncrojt