ON THE EXAMINATION OF SOILS 147 



now add 30 cc. of potassium sulphide solution 

 (40 grams in 1000 cc. water), and after shaking 

 add 80 cc. of a saturated caustic soda solution or 

 enough to make it alkaline. Connect at once with 

 the condenser, and distill over about 125 cc., receiv- 

 ing into a measured quantity of standard acid, and 

 then titrate with standard alkali, using cochineal 

 as indicator. One cc. of the decinormal sulphuric 

 acid is equal to .0014 gram of nitrogen. 



In the absence of nitrates the salicylic acid 

 may be omitted from the sulphuric acid; other- 

 wise the nitrogen determination is made the 

 same way as above, with varying amount of 

 substances to be analyzed, according to its 

 nitrogen content. 



Phosphoric Acid. Ten grams of the sifter soil, 

 dried at 100 C., are charred if organic matter 

 be present. The charred mass is moistened with 

 water and afterwards with nitric acid, until 

 the carbonates are decomposed. The mass is 

 digested with ten cubic centimeters of nitric 

 acid for two hours at about 100 C. with fre- 

 quent stirrings and the addition of fresh acid, 

 from time to time, to replace that which has 

 been evaporated. After filtering and washing 

 with hot water the filtrate is evaporated to a 

 volume of 50 cc. and treated with five cubic 

 centimeters of concentrated nitric acid and half 

 a gram of crystals of chromic acid. After covering 

 the dish with a funnel to return condensed 

 vapors its contents are heated to the boiling 



