RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



Chemical investigation of amylases and related enzyms, II. C. Siiekman 

 {Carnegie Inst. Wash. Year Book, 18 (1919), pp. 328-330) .—This is the annual 

 progress report of the author's investigations of amylases and related enzyms. 

 In addition to the continuation of the studies referred to in tlie report of the 

 previous year (E. S. K., 40, p. 60S), an extended study has been begun of the 

 effects of amino acids upon the enzymic hydrolysis of starch by different 

 amylases. The results of this study as so far published have been noted from 

 another source (E. S. K., 42, p. 203). 



Determination of small quantities of iron, M. L. Mathieu (Bui. Assoc. 

 Chim. Sucr. ct Distill., 37 (I'.IW), No. 6, pp. 205-20S) .—Sources of error in the 

 usual colorimetric methods for the determination of small amounts of iron are 

 noted, and a method is described which is said to avoid these errors. 



The method as applied to wine must consists in evaporating 5 or 10 cc. of the 

 Siimple in a platinum crucible and ashing at low red heat. The ash is taken up 

 in 5 cc. of HCl (1 : 4), 10 cc. of a 1 i)er cent solution of KCN.S is added, and the 

 contents of the crucible are washed into a graduated tube and made up to 50 

 cc. This is checked with iv similar tube to which is added from a burette a 

 solution of pure ferric chlorid containing 0.0001 gm. in 1 cc. until the color is 

 Identical with that of the tube containing the sample. 



The test is said to be sensitive between the limits of 0.01 and 0.2 mg. of iron 

 in 10 cc. 



Some factors influencing the quantitative determination of clilorids in 

 soil, C. T. HiKST and J. E. Greaves (l-^oil SH., 9 (1!)20), No. 1, pp. 41-51). — 

 Experiments conducted at the Utah Elxperiment Station with a heavy black clay 

 loam soil to study factors influencing the determination of clilorids in soils are 

 reported. The work was based on the Mohr and A'olhard methods. 



It was found that equally satisfactoiy soil extracts from which the chlorids 

 are to be determined are obtained either by the use of 2 gm. of alum or by the 

 Pasteur-Chamberland filter. The extract obtained by use of the centrifuge gave 

 higher results, due perhaps lo the presence of proteins or other colloids in sus- 

 pension. The quantity of chlorids obtained by the use of 5 parts of water to 

 1 part of soil was the same as with larger quantities of water. It was found 

 that nothing is to be gained by agitating the soil and water for more than five 

 minutes if the soil is finely divided and the solution vigorously shaken. The 

 Mohr and Volhard methods gave low results in the presence of nitrates of the 

 alkali and the alkali earths, and the Volhard method low results in the presence 

 of carbonates of the alkali and alkali earths. The Mohr method gave high 

 results iu the presence of carbonates due to the precipitation of silver carbonate. 

 The Volhard method gave more concordant and, as judged by the gravimetric 

 method, more nearly exact results than the IMohr method. Ethyl alcohol caused 

 tlie coagulation of silver chlorid as well as ether or boiling. 



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