154 abstracts: physics and chemistry 



AGRICULTURAL PHYSICS.— The electrical bridge for the deter- 

 mination of soluble salts in soil. R. O. E. Davis and H. Bryan. 

 Bulletin Bureau of Soils, No. 61. 1911. 



The bulletin contains a complete description of the modified Wheat- 

 stone bridge as used by the Bureau of Soils with considerable experi- 

 mental data on its efficiency. Working drawings and cuts of the instru- 

 ment are included in the description. Conclusions reached from the 

 experiments are : Difference in texture of soils influences the resistances 

 of the soil; the presence of carbonates changes the resistance so greatly 

 that with black alkali a special table must be used; organic matter in 

 large amounts increases the resistance, the same amount of salt being 

 present; and when a soil is in a dry condition, at least twenty minutes 

 should elapse after moistening before the reading for resistance is made. 



R. 0. E. D. and H. B. 



AGRICULTURAL CHEMISTRY.— The isolation of creatinine from 

 soils. Edmund C. Shorey. Science 33: 340. 1911. 



Creatinine has been isolated from several soils by the following 

 method. An extract made by shaking the soil for half an hour with 

 2 per cent sodium hydroxide is neutralized with acetic acid and filtered. 

 To the filtrate a small quantity of dextrose is added, after heating to 

 boiling, Fehling's solution is added until the precipitate formed is red. 

 The precipitate after washing is decomposed with hydrogen sulphide 

 concentrated under reduced pressure. Creatinine, if present in the soil, 

 is in this filtrate together with purine bases. It can be separated as 

 creatinine zinc chloride and creatinine prepared from this by treatment 

 with lead hydroxide. The creatinine was identified by the character- 

 istic crystalline appearance of the zinc chloride compound and by the 

 Jaff6, Weyl and Salkowski color reactions. M. X. Sullivan. 



AGRICULTURAL CHEMISTRY.— Reduction by roots. Oswald 

 Schreiner and M. X. Sullivan. Botanical Gazette, 51: 121. 

 1911. 



Plant roots have the power to reduce sodium tellurite and selenite to 

 metallic tellurium and selenium. The reducing action of the growing 

 root is stronger in the young seedling, being much stronger in a seedling 

 four days old than in one twelve days old. 



As judged by the quickness with which the selenium deposits on the 

 roots and the extent and intensity of the deposit, the reducing power 



