6l6 AGRICULTURAL ANALYSIS 



may be dissolved and the phosphoric acid determined after sep- 

 aration with ammonium molybdate. 



Sulfuric Acid. Fifty cubic centimeters of the original hydro- 

 chloric acid filtrate, obtained as described under the determina- 

 tions of sand, silica and carbon, are heated to boiling, and the 

 sulfuric acid thrown out by the gradual addition of barium 

 chlorid. During the precipitation the mixture is kept at the boil- 

 ing temperature, but taken from trie lamp and the precipitate 

 allowed to settle from time to time until it is seen that an addi- 

 tional drop of the reagent causes no further precipitate. The 

 barium sulfate is collected, dried, and weighed in the usual man- 

 ner. 



Chlorin. Dissolve from one to five grams of the' ash in nitric 

 acid in very slight excess, or in water. If the solution be made 

 in nitric acid the excess must be neutralized if the chldrin be de- 

 termined volumetrically ; and if the solution be in water, nitric 

 acid must be added if the determination be gravimetric. 



The volumetric determination is accomplished in the usual 

 manner with a standard silver nitrate solution, using potassium 

 chromate as indicator. The gravimetric determination is effected 

 by precipitation with silver nitrate, collecting, washing, and dry- 

 ing at 150 the silver chlorid obtained. 



Carbon Dioxid. The carbon dioxid is most conveniently esti- 

 mated in from one to five grams of the ash, according to its rich- 

 ness in carbonates, by the apparatus described in Volume I or 

 some similar device. 87 



521. Early Official Method for Determinations of the Alkalies. 

 Evaporate the filtrate and washings from the sulfuric acid de- 

 termination, paragraph 519 in a porcelain dish to dryness, re-dis- 

 solve in about 50 cubic centimeters of water and add milk of lime, 

 or barium hydroxid solution, which must be perfectly free from 

 alkalies, until no further precipitation is produced, and it is evi- 

 dent there is an excess of calcium hydroxid or barium hydroxid 

 present ; boil for two or three minutes, filter hot, and wash thor- 

 oughly with boiling water, precipitate the lime and baryta from 



87 Wiley, Principles and Practice of Agricultural Analysis, and Edition, 

 1906, 1 : 380. 



