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diameter of the spherical bead. Aside from this work, which can be properly classified as chemical microscopy, no attem pt had been made purposely to reduce the quantities of material in chemical operations. Emich’s decision to inquire generally into the lower limits of chemical experimentation started the development of a microtechnique of chemistry, with Emich blazing the trails in all directions. His exact share in the work cannot be overestimated, since his advice was generously avail
able for everybody. Every work emanating from his own laboratory is not always recognizable as such. Very often only the name of his co-worker appears as author, in spite of the fact th a t Emich rarely suggested an investigation without having done sufficient experimental work to be assured of a satisfactory solution.
By 1911, the year of the publication of Emich’s “Lehrbuch der Mikrochemie” (16), the complete outline of microchem
istry was established, mostly on the basis of the experimental work of Emich and his assistant, Julius Donau. The tech
nique of qualitative analysis of milligram samples with the use of microcones of 0.7-ml. capacity had been developed and tested. The development of the fiber technique (12, 19, 20) led to the discovery of confirmatory tests with limits of iden
tification as low as 10~10 gram, and perm itted simple chemical operations with fractions of a microgram of material. The invention of the coloriscopic capillary (83) extended the use
fulness of colorations for the detection of small quantities of materials, and _ perm itted absorption spectroscopy and polarimetry (8) on small volumes of liquids.
The suitability for chemical work of simple balances con
structed of glass or quartz had been demonstrated by W alter N ernst in 1903; he used such a balance for weighing small samples of inorganic substances for the determination of the vapor density in a small platinum apparatus, utilizing the principle of Victor Meyer (44). The same balance was also used by N ernst and Riesenfeld (46) for residue determina
tions on small samples. Brill and Evans (7) performed quantitative determinations of small quantities of metals by electrolytic precipitation. Emich (34) was the first to carry out a procedure for the quantitative collection of small amounts of precipitates, and his co-worker Donau performed quantitative determinations on samples weighing a few milligrams w ith and w ithout previous separations. Micro- Carius determinations of halogen and sulfur in organic sub
stances were tried and gave satisfactory results. Procedures for the titrim etric determination of small quantities of sub
stances had been worked out by D utoit (10), Ebler (11), and Zsigmondy and Heyer (63). Emich’s co-worker Pilch (46), however, was probably the first to perform micro-Kjeldahl determinations.
There is no doubt th a t microchemistry, which would have been a badly chosen synonym for chemical microscopy in 1900, had emerged by 1910 as an established branch of science because of Em ich’s efforts as investigator, inventor, organizer, and propagator. His summarizing lectures before learned societies such as the Deutsche chemische Gesellschaft (14), the Verein deutscher Naturforscher und Aerzte (26), and the Verein österreichischer Chemiker (27), as well as the publica
tion of his Lehrbuch, could not fail to further the general recognition of the field, accomplishments, and applications of chemical micromethods.
After 1910 new centers of microchemical research began to appear. Krogh (41) had published in 1908 a paper on gas microanalysis which opened a distinct line of endeavor. The discovery of radioactive elements necessitated accurate residue determinations on small quantities of material for the determination of atomic weights. This, among other things, led to the construction of extremely sensitive quartz balances such as those of Gray and Ramsay (38).
The impossibility of analyzing the small amounts of organic APRIL 15, 1940
substances isolated from gallstones would have forced Pregl in 1909 to sta rt with considerably larger quantities of raw material. Emich’s success in developing quantitative micro
methods, however, opened another alternative, undreamed of before th a t time. He decided to develop micromethods for the quantitative elementary analysis of organic substances.
Work in the same direction had been started in Em ich’s laboratory, b u t it was now decided to cede this field to Pregl.
The possible consequences of this decision m ay no t have been considered by Emich, who always was fascinated by the diffi
culties of a problem or the ingenuity of its possible solution rather than by its practical merits. Pregl reported on his methods of elementary analysis a t a meeting of the Deutsche chemische Gesellschaft in Berlin on February 27, 1911.
The existent need for procedures of organic microanalysis gave the interest in microchemistry a strong impetus which received a renewed impulse with the publication in 1913 of Bang’s papers (6) on the microdetermination of blood con
stituents. The same year brought the publication of the books by Molisch and Tunm ann on the microchemistry of plants. From approximately 1910 to 1930 organic elementary analysis and biochemical methods were the branches of micro
chemistry on which general interest was centered. By 1920 regard for these branches reached its peak, and microchem
istry was in the limelight.
Emich held to his agreement with Pregl, and continued his admirable work on the general development of technique.
While his co-worker Donau continued to improve methods for the quantitative collection of precipitates (9), Emich started a comprehensive study of balances suitable for microchemical work (21).
The original balance of Nernst had been already modified; now Emich designed two balances of the Nernst type with sensitivities of 0.3 and 0.1 microgram. A quartz balance with electromagnetic compensation with a sensitivity of 0.015 microgram was con
structed. Since the magnet and the dish with the substance were placed on the same side of the beam, the mass determined was actually carried by the electromagnetic force only and, no matter whether the weighing dish was empty or full, the light quartz beam always carried the same load a t the time of the reading.
Residue determinations were carried out with samples weighing 12 to 92 micrograms. The spring balance of Salvioni was simpli
fied for the rapid estimation of masses of a few milligrams on the workbench. Another spring balance, using the principle of Jolly, was designed for lecture demonstrations of the laws of constant and multiple proportions, the determination of gas density, the determination of the molecular weight of organic compounds, and the demonstration of the volatility of platinum and quartz at higher temperatures. Suitable steel springs permitted the attainment of a sensitivity of 30 micrograms. The outlines of a platinum foil triangle attached to the end of the spring were pro
jected on a millimeter scale approximately 2 meters long, so that the audience was enabled to check on the readings. Fifteen years later, the work with the electromagnetic balance was resumed, and residue determinations as well as electrolytic determinations were carried out on samples of 2 to 6 micrograms (52).
The investigation of paint films on an object of art led Emich to the development of a technique for the performance of chemical work in capillaries. The first publication dealt iece of red litmus paper. Thus, 0.1 microgram of nitrogen could e detected. An adaptation of the Carius procedure to the capillary technique permitted the detection of 0.05 microgram of sulfur or phosphorus in organic substances (82), and ignition in an oxygen-filled tube followed by precipitation of the carbon dioxide as calcium carbonate gave 0.001 microgram of carbon as the limit of identification. The determination of the boiling point was made possible with the use of only 0.5 cu. nun. of liquid ANALYTICAL EDITION 227
228 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 12, NO. 4 (22), and the possibility of simple organic syntheses in capillaries
with a few milligrams of substance was thoroughly investigated (85). The performance of reactions in either closed or open capillaries presented no difficulties.
For the isolation and purification of the products, pro
cedures for the recrystallization from hot solutions, the blood- charcoal treatm ent, the filtration of hot solutions, the evapora
tion of solvent, distillation, sublimation, washing, and drying had to be worked out.
As a principle, transfer of material from one capillary to another was avoided to reduce the loss to a minimum. Thus, it became possible to perform simple syntheses. The products were isolated and purified in the same tube in which the reaction had been car
ried out, and the melting point was determined between the operations of purification until its constancy indicated a satis
factory degree of purity. A small Carius oven, permitting violent agitation of the contents of capillaries with bulb-shaped ends, had been designed by Emich for his lecture demonstrations in organic chemistry (2), and a centrifuge head for the shaking of capillaries was described later (51). Zinc dust distillations were carried out, including isolation of the products. For the fractional distilla
tion of 0.05 to 0.1 ml. of liquid (42), a centrifuge cone with a
determinations w ith milligram samples. Pregl’s work had practically come to a conclusion a t this time, and Emich no longer hesitated to make use of K uhlm ann’s microchemical balance, which had become the supporting pillar of Pregl’s procedures. Three methods of working were tested.
In the first, the precipitate was collected, washed, and dried
The sample was dissolved in the beaker and the precipitation car
ried out, and finally the spout was connected to a suction flask and the precipitate collected and washed on the filter m at of the outlet. After drying, the third weighing was made.
The last and most practical procedure was based on the use of an immersion filter and a microbeaker (49). The two were always weighed together, so th at a complete transference of the pre
cipitate into the filter, the “filter stick”, became unnecessary.
Beaker and stick could be made of glass, porcelain, quartz, or platinum and thus the ignition of precipitates became possible.
All three methods avoid a quantitative transfer of the precipitate; the constituent determined remains essentially in the same container from the sta rt to finish, and three weighings suffice for any determination. The use of the centrifuge tube proved somewhat clumsy and is practically forgotten. Filter stick and filter beaker, however, have stood the test of time, and have been used in involved analyses
One solution was taken up in a capillary pipet, the tip of which was inserted into the other solution contained in a small glass cell with plane-parallel walls. The long fine tip of the capillary pipet
reduced to a minimum the rate of outflow and the kinetic energy of the liquid leaving the tip of the pipet. Thus, the liquid of the pipet would start to fall or rise in the cell liquid, depending upon tneir relative densities. The sign of the deviation of their refractive indices was simultaneously recognized by the kind and distribution of striations marking the boundary of the stream of pipet liquid in the cell liquid. The phenomena were studied with optical setups of different sensitivity. Besides an impressive bench arrangement 8 yards long, specially constructed Schliereti- microscopes, simple setups according to Dvordk, and extremely primitive arrangements using nothing but a black and white background were employed. A method for the determination of the concentration of solutions was developed.
The purity of substances was tested by comparing the frac
tions of distillations and fractional crystallizations, c . p. benzene required three fractional distillations with eight fractional in
termediate crystallizations before appearing pure when tested with the methods evolved. Theoretically curious results were obtained when solutions were allowed to flow into other solutions of the same refractive index but different chemical composition.
Finally the Schlieren technique was used in the observation of the changes at the critical temperature (39). A simple experimental arrangement was developed, and the usefulness of the determi
nation of the critical temperature for the identification of small quantities of material was demonstrated.
M any details have had to be omitted in this brief outline of Emich’s research work. Several microscopic confirmatory tests were worked out or suggested by him—e. g., sulfur in inorganic and organic compounds (30), rubidium, cesium (23), mercury (31), them orin test for aluminum (48), the Rinm an’s green test for zinc (6’), and the bead test for cobalt (43). In m any of the large number of lecture experiments devised, he utilized microchemical methods. Among the most interesting were the demonstration of the hydrolysis of sodium chloride a t high tem peratures (13), the thermoluminescence of iodine and bromine vapors (28), the formation of protuberances and the method of making them visible (28), and finally the demonstration of the action of enzymes with the Schlieren method.
The second edition of Em ich’s “Lehrbuch der Mikrochemie”
(16) was published in 1926. His “Mikrochemisches Prakti- kum ” (18) was translated into English and Russian. Among other comprehensive compilations m ust be mentioned his contributions to Abderhalden’s “Iiandbuch der biologischen Arbeitsmethoden” (1), and to Staehler-Tiede-Richter’s
“Iiandbuch der Arbeitsmethoden in der anorganischen Chemie” (50). Emich also covered the development of microchemistry from the early beginnings to 1915 in reports to various journals (14, 15, 17). A lengthy report on the ad
vances from 1915 to 1926 (40) is based on his literature notes.
The increasing attention attracted by microchemical methods combined with publication of Em ich’s laboratory manual brought a steadily trickling stream of visitors from all countries to Emicli’s laboratory. Some of Pregl’s visiting students dropped in, and some of these decided to come back for a longer stay. Invariably, the visitors and guests were impressed by Emich’s scientific integrity and sincere kindness. Friendships and attachm ents started which were bound to last. Then, too, the practical importance of Emich’s life work was recognized more and more. Tech
nical men, mineralogists, archeologists, curators of a rt col
lections, biologists, and medical men began to recognize the aids offered for the solution of their problems which, in the course of general progress, had become of a more minute nature.
H o n o r s
Emich received medals for meritorious service from both the Imperial Government and the Republic of Austria. He was awarded the Lieben prize and the Liebig Memorial Medal. In 1918 he became a corresponding member of the
APRIL 15,1940 ANALYTICAL EDITION 229 fluorescence produced in solutions containing aluminum by addition of morin, first observed by Goppelsroeder (4), accuracy in the quantitative estimation of aluminum a t con
centrations ranging from 0.1 to 1.2 mg. of aluminum per liter.
The range of usefulness may be extended to higher concentra
tions by dilution to within these limits. The method requires
the use of a source of ultraviolet radiation for producing the fluorescence, which may then be measured w ith either a visual or photoelectric photometer. Having determined a calibra
tion curve, an analysis m ay be accomplished very quickly, the whole procedure being admirably suited to routine control of small amounts of aluminum.
E x p e r im e n ta l D e t a ils
A Hanovia quartz mercury vapor lamp was used as a source of ultraviolet radiation where the fluorescence was measured with the Pulfrich photometer. A purple filter, 5 mm. thick, was used with this to eliminate most of the visible radiation. Observations were made at right angles to the source of ultraviolet light. Cells 2.0 X 1.8 cm. were used, arranged so that the thickness pene
trated was the 1.8 dimension.
Photoelectric measurements were made with an apparatus essentially as described by Hand (5) and improved by Levin (6).
A 5-cm. (2-inch) cubical cell was used to contain the solution and a Wratten No. 8 yellow filter was placed between this and a Gen
eral Electric photronic cell. The ammeter employed had 150 scale divisions in microamperes and the tenths listed in the tables below are estimations. A fluorescein solution was used periodi
cally in checking the constancy of the intensity of the light source.
It was found that fluctuations were not of an order to warrant making corrections.
Standard aluminum solutions were prepared by dissolving potassium aluminum sulfate crystals in warm distilled water with addition of 2 ml. of 6 M acetic acid per liter to prevent hydrolysis.
Intermediate concentrations for calibration curves were obtained by dilution. Morin, the dyestuff principle of 'ustic wood, was