§ 119. SUPERPHOSPHATES. 235 



h. JVon-VOlatilc matters. — Ignite the dry residue ob- 

 tained in a (§ 91). 



c. Nitrogen. — This should be determined, in case the 

 ]>hosphate was prepared from Peruvian guano or bone- 

 meal, or it is claimed that it contains nitrogenous matter. 

 Ignite 0.5-1 grm. with soda-lime. 



d. Actual ammonia. — Determine this, if present, by 

 Schlossing's process, in 1-2 grms. (§ 47, h). 



e. Phosphoric acid. — The value of a superphosphate 

 depends chiefly upon the amount of phosphate that it con- 

 tains that is soluble in water, and, when the article was 

 prepared from bone-black, bone-ash, phosphorite, or Baker 

 guano, the determination of soluble phosi:)hate suffices for 

 the estimation of its value. But when made from steamed 

 bones, wholly or in part, there is commonly from 5-6" |„ of 

 insoluble phosphate which should be taken into account. 

 It appears that sometimes the proportion of soluble phos- 

 phate diminishes when the article is kept for a long time ; 

 if, therefore, an unexpectedly small amount is found, a 

 determination of the insoluble phosphate should be made 

 also, in order to estimate fairly the value of the fertilizer. 



1. To estimate the 8 ohihle phosphate^ triturate 10 grms. 

 of the well-mixed sample with 200-300 c.c. of water, ap- 

 plying pressure enough with the pestle to break up the 

 lumps, but not to pulverize the hard grains ; let the mix- 

 ture stand some time, pour oif the clear supernatant liquid 

 through a filter, and repeat the exhaustion with water as 

 long as an acid reaction is communicated to a fresh por- 

 tion ; finally, put the whole insoluble residue on the filter, 

 dry it at 100°, and weigh it ; bring the volume of the 

 aqueous extract to 1000 c.c. 



Determine phosphoric acid by the volumetric method 

 in 100 c.c. of this solution, first precipitating and filtering 

 out the ferric phosphate, if but a small quantity is formed, 

 and dry and Aveigh this precipitate ; 47.02" |„ of it is phos- 



