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INSTRUMENTATION Apparatus for automatic weighing and recording of results may open the w a y to many new analytical techniques

CONTINUE to insist that autoWEmatic weighing (and recording the

results) might be the "Open sesame" to many new techniques for the analytical chemist. We thought so in ] 938, when the ingenious and resourceful Ray Garman helped us build a recording analytical balance, duly described that year in the pages of this journal, Our good friend, Professor Clement Duval in Paris clinched this opinion, not in another paper, but in a memorable monograph which, for all time, put inorganic gravimetric analysis on a convincing, graphic, and demonstrable basis. As a result of his stupendous labor, one may now know precisely what happens when a precipitate is ignited; one may renew his faith in stoichiometry and may see for himself what lies between those two widely divergent goal posts—"taken and found." All of this we have said several times, but it is characteristic of what passes for the scientific age that one must repeat the obvious continuously and incessantly before it is recognized as significant. There have been sporadic efforts here and there to use Duval's techniques, but in our humble opinion, entirely too few. We believe that M. Duval would agree that the Chevenard balance, or any other example of recording balance, might be applied in a dozen categories of analytical importance, other than those which he used with such signal success. It comes to our attention that among several extremely selective segments of the American instrument industry, there is now grave concern among balance manufacturers about the heavy influx of foreign balances. This apprehension seems to be shared by the American manufacturers of microscopes and other producers of essentially nineteenth century devices. We hear no cries of alarm from producers of indicating, controlling, or recording potentiometers, nuV O L U M E 2 7, N O . 2, F E B R U A R Y

clear instruments, or electronic devices. Curiously enough, there is a strange correlation between the research and publication activities of a company and its shrieks for congressional action in protective tariffs. We leave the subtleties and details of these matters to SAMA—frankly, they are too technical for us. Recording

Balances

To return to the matter of recordingbalances—there are only two to be had for any price and both are foreign, one from the famous and charming M. Chevenard in Paris and the other from Western Germany, obtainable through Brinkman in this country. Our own manufacturers will ask immediately, "Why build a recording balance? Who will use it, for what problem will he want one, and what will he be willing to pay for it?" Having raised the point, we shall now retreat in haste and take refuge in a vague reference to a related field. Twenty-five or 30 years ago, anyone who suggested the use of a phototube in analytical chemistry was, in a sense, slightly idiotic or at least a "gadgeteer." A large portion of modern analytical chemistry may now be classified as B.B. or A.B. which, as everyone knows, means "before Beckman" or "after Beckman," because that illustrious pioneer in chemical instrumentation, after licking the tough problem of electronic instrumentation for the glass electrode, turned his attention to spectrophotometry, and despite all the academic proofs to the contrary, proved that a phototube could indeed be depended upon to supply reliable analytical information. He accomplished far more than he might have dreamed. The famous D.U. is now so simple, reliable, and dependable that neither professor nor student need bother about the messy optics or electronics—the 1955

by Ralph H. Miller

absorbances come out—regularly and reliably. The operation is so simple that it is only a matter of time before doctoral dissertations will no longer be granted for pouring solutions in the hopper. If anyone is still following the argument, a recording balance has a comparable future and extremely widespread use. The bottleneck lies in a matter of definition. Any college freshman can answer the question "Of what use is an analytical balance?" "Why, to weigh, of course!" Therein lies the essentially limiting fallacy. Aside from Duval's brilliant application, a recording balance could supply a hundred distinct records of reaction mechanism kinetics, equilibria, and other information, the like of which has not been seen. I t is with extreme regret and chagrin that we admit that instrumentation has, in large measure, given false emphasis to many analysts. All too often, it is assumed that instruments will enable us to do nineteenth or eighteenth century tasks automatically and without expensive human effort. We insist that the modern instrument should give us continuous and voluminous information about the mechanism of processes and operations. To be exceedingly repetitious, we again ask the reader to examine Duval's pyrolysis curve for calcium oxalate! We all admit that it is a rare example, but despite this, it is worth ten lectures on gravimetric analysis. 41 A

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INSTRUMENTATION

Now, if Nero fiddled while Rome burned, let us see what is happening in industry. According to Chemical Proc­ essing [18, No. 1, 17 (1955)], Fairbanks, Morse & Co., 600 South Michigan Ave., Chicago 5, 111., have developed a 10,000 and 5000-pound scale which records in­ gredient weights on a printed tape locked up inside the scale for the pur­ pose of protecting this secret informa­ tion even from the firm's own employees! It was designed to protect the formula of a noted brewing company—whether from duplication, or from lawsuit by the consumers of the product, is not stated. In the absence of definite information we are inclined to the more charitable interpretation. As any well informed reader knows, Fairbanks, Morse & Co. are pioneers in precise industrial weigh­ ing and have many notable achieve­ ments to their credit. This one is un­ doubtedly among them; but is it not curious that although the research ana­ lyst rarely thinks about automatic weigh­ ing, industry is not only doing this, but has surrounded the entire operation with precautionary measures over and above the technical difficulties? We may as well admit at this point that in addition to being slightly slow-witted by nature, we do not really understand what is meant by that modern slogan— "Research." At last count, we listed eight possible approaches to automatic weighing, only two of which have been used in previous instruments. Some of these are being studied, but as we have intimated, it must be shown how these things can be used with profit. That is, by far, the larger problem. Instruments

for the

Biologist

Physical and analytical instruments for the biologist and clinician will con­ tinue to be the concern of the analytical chemist. This is so because the analyst is particularly fitted to exercise his critical faculties in such situations. As we have pointed out on numerous occasions, clinical chemistry is in dire need of ad­ vanced instrumental techniques. The great advance was made more than a quarter of a century ago by the intro­ duction of microprocedures for blood analysis, as a consequence of which there was a decided shift in emphasis from urine analysis to blood analysis. However, very few determinations can be carried out without removal of a sample, however small. Furthermore, in many cases, one must be "half-dead" before significant changes show up. The matter of "normal variations" is extremely unsatisfactory and very often one is confronted with three not too clearly delineated choices—recheck the reagents, resort to surgery, or seek ANALYTICAL

CHEMISTRY

INSTRUMENTATION

Mass Spectrometry...

"spiritual consolation." O u r 13 years connection with this field, happily terminated b y World W a r I I , left us extremely u n h a p p y a n d convinced t h a t " n o r m a l r a n g e " encompasses a regime in which one m a y feel " h i g h " or " m i g h t y low." W e risk censure or ridicule b y suggesting t h a t a continuous automatic record of a n y significant constituent might show interesting a n d suggestive relations.

on a practical industrial basis T w o companion instruments, Types 21-610 and 21-620, now extend the speed and accuracy of mass spectrometric analysis from the laboratory out into the plant. Flexible and simplified, needing only 115 volts and a small supply of cooling water, the twin instruments are easily adaptable t o process-stream monitoring, batch work, or leak detection.

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TYPE 21-610 is moderately priced and a truly general-purpose instrument. Although primarily designed for continuous petroleum and petrochemical stream analysis, it is also valuable as a production-line leak detector or laboratory analytical instrument. It has been used in applications ranging from on-the-spot acetylene-plant monitoring to hospital clinical tests on lungs.

TYPE 21-620 has the highest mass range of any instrument in its compact size range. Using the newly developed "Cycloidal Focusing" principle for analysis, it goes beyond the 21-610 for accurate readings from mass 2 to mass 150. Medical laboratories, petro-chemical plants and general research organizations will all find it an ideal answer to their analytical problems.

Modifications . . . accessories The 21-610 may be converted to a 21-620 whenever the latter's greater resolving power is needed. The work is accomplished by a CEC Field Service Engineer without return of the instrument to the factory. Involving primarily the exchange of some components and the addition of certain others, the conversion is made reasonably and quickly. An extensive accessory line greatly broadens the utility of both the 21-610 and 21-620. Automatic peak selectors scan as many as six mass numbers on a repetitive cycle; sampling probes and magnet shunts make either instrument a practical production-line leak detector; batch-sample inlet systems and continuouschart recorders (left) may be mounted directly on the instruments. How industrial mass spectrometry can be used in your business is explained in Bulletin CEC 1824A-X11. Send for your copy.

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in Expired Air

Another milestone in q u a n t i t a t i v e information provides means for recording the moisture in expired air, i n this case b y detecting a n d recording t h e moisture as a change in effective dielectric constant of t h e air-moisture mixture. T h e interest resided in t h e need for studies of subjects under cold ambient conditions. All this is t o be learned from a paper b y Paul W e b b and M . K . Newgebauer [Rev. Sci. Instr., 2 5 , 1212 (1954)]. Electronically, t h e syst e m seems complex, b u t i t is a straightforward application of a sensing capacitor which shifts the frequency of a 2 me. variable Clapp oscillator. This beats against a 2 mc. crystal-controlled reference oscillator. A mixer stage sends the difference frequency t o clipper and pulse shaping circuits from which a multivibrator, integrator, a n d d.c. a m plifier feed t h e o u t p u t t o a pen motor. Provision is made t o check t h e system against a reference 480 c.p.s. oscillator. Advantages claimed for t h e dielectric hygrometer a r e : I t does n o t alter properties of t h e air stream being measured; t h e measuring element is small; it is capable of high accuracy; t h e response is rapid; and i t is useful in a wide range of ambient temperatures. Subminiature

Triode

T h e R C A 5734 subminiature triode is a n electromechanical transducer in which t h e anode extends as a pin through a diaphragm. Extremely small and limited motion of this pin leads t o large changes i n anode-cathode resistance. I t has»been adapted t o a simple electromanometer b y M . Ainsworth and J . W . Eveleigh [J. Sci. Instr., 3 1 , 471 (1954)], in which a diaphragm or bellows is coupled to t h e anode pin. I n a specific case, the motion of t h e anode pin was limited b y mechanical stops t o ± 5 microns (linear displacement, n o t pressure) for which t h e o u t p u t from a balanced measuring circuit was 6 volts. In an actual combination with bellows, in a differential arrangement for a pressure range of 0 to 3 m m . of mercury and a resonance frequency of 110 cycles per second, the o u t p u t was linear and gave about 5-volt signal for the 0 to 3 m m . of mercury pressure extreme. ANALYTICAL

CHEMISTRY