EXPERIMENT STATION RECORD. 



Vol. XXX. Arstkact Xumbkk. No. 9. 



RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



Introdaction to biochemistry, W. Lob {FAnfuhrung in die BiocJiemie. Leip- 

 (iic, 1911, pp. S3, figs. 12). — This is a small book intended to serve as an intro- 

 duction to biochemistry. It is a compilation of a series of lectures given in 

 public high schools. The plant and animal kingdom are both considered. 



The bearing" of osmotic pressure on the development of physical or gen- 

 eral chemistry, H. C. JoNi;s (Phint World, 16 {1913), No. S, pp. 7.?-^8).— This 

 topic is discussed for the purpose of showing its importance in relation to the 

 biologic sciences. 



The reduction of arsenic acid to arsenious acid by thiosulphuric acid, 

 R. :M. Chapin (U. S. Dcpt. A(/r., Jour. Agr. Research, 1 (1914), No. 6, pp. 515- 

 517). — "While endeavoring to work out a practicable field method for the 

 estimation of the total arsenic — that is, a method which should include both 

 arsenites and arsenates — in arsenical baths used for dipping cattle, studies 

 were made upon the effect of various reducing agents which are able to absorb 

 iodin in acid solution upon the well-known reversible reaction, As (OH) 3+21 + 

 2H20fz;As(OH)5+2ni. Unless the solution in which this reaction is taking 

 place is freely acidified with a strong mineral acid or heated, the progress of 

 the reaction from right to left is inconveniently slow." 



It was found, however, that sodium thiosulphate greatly aided the reduction, 

 and further, that the presence of hydriodic acid played no part in the reduction 

 of arsenic to arsenious acid. This reaction can be effected by sodium thiosul- 

 phate and mineral acid alone. 



The present series of exi^eriments was limited to a study of the reactions 

 occurring when a mixture of arsenic acid, or arsenate, with an excess of 

 sodium thiosulphate is acidified with a definite amount of hydrochloric or 

 sulphuric acid, as this condition must prevail in any quantitative method for 

 the determination of arsenic based on these reactions. The solutions employed 

 were "(1) a tenth-normal (oxidimetric) solution of arsenic acid prepared by 

 oxidizing arsenious acid with nitric acid and expelling excess of the latter, 

 (2) a tenth-normal solution of sodiimi thiosulphate, (3) a twentieth-normal 

 solution of iodin, free from iodate, and (4) normal hydrochloric acid." 



From the experiments it is obvious that the action of thiosulphuric acid upon 

 arsenic acid appears to be closely similar to the action of thiosulphuric acid on 

 bichromic acid. A small amount of the thiosulphuric acid is decomposed into 

 sulphur dioxid, and presumably, sulphur, but this does not become evident. 



801 



