500 BELL SYSTEM TECHNICAL JOURNAL 



which may be readily centrifuged, filtered and washed, and which 

 exhibit a minimum tendency to adhere to the wall of the containing 

 vessel. The simple insoluble salts, oxides or hydroxides usually 

 obtained in the older, classical methods, rarely meet these requirements 

 satisfactorily and recently much attention has been given the search 

 for more suitable quantitative precipitants. The result has been an 

 increased use in microwork of organic, complex and double salts of 

 high molecular weight. Thus sodium is no longer weighed as the 

 sulphate, which provides only a threefold increase in the weight of the 

 sodium present, but rather as crystalline sodium zinc uranyl acetate 

 having a molecular weight of 1591 or a weight equal to 69 times that 

 of the sodium present. Silver may be collected and weighed as silver- 

 copper propylenediamine iodide of molecular weight 939. Aluminum, 

 instead of being precipitated as gelatinous aluminum hydroxide, which 

 is difficult to filter, may be separated and weighed as the crystalline 

 oxy-quinolate with an eighteen-fold increase in weight. 



Another possibility of chemically amplifying weight consists of 

 employing a train of reactions the final weighable product of which 

 has a high molecular weight. Although it may not contain the 

 element originally sought, this product is still stoichiometrically related 

 to it and provides the basis for quantitative estimation. 



Although Pregl, Emich and Chamot are considered the founders of 

 modern microchemistry, there were a number of earlier isolated in- 

 stances of such methods being used. The earliest attempt to organize 

 qualitative microchemical methods systematically was made by 

 Boricky in 1877 who applied the technique to petrographic studies and 

 wrote a treatise entitled "Elements of a New Microchemical Analysis 

 of Minerals and Stones." In 1885, Haushofer in his book "Mikro- 

 skopische Reaktionen " provided a rather complete description of reac- 

 tions carried out under the microscope, his work covering most of the 

 common elements. It remained for Professor H. Behrens of Delft, 

 Holland, and H. Schoorl to expand the technique to a point where 

 minute quantities of substances could actually be separated and 

 manipulated to permit the application of common analytical opera- 

 tions. In the biological field, H. Molisch developed the technique of 

 applying microreactions directly to plant tissues and in this way was 

 able to identify many intracellular substances. His book "Mikro- 

 chemie der Pflanze," and that of Mayerhofer, "Mikrochemie der 

 Arzneimittel und Gifte," are well known. 



In Europe, particularly in Germany and Austria, awakening interest 

 in the application of microchemical methods to industrial problems is 

 evidenced by the appearance of a large number of articles on the 



