§ 117. BOXE-BLACK, BONE-ASH, PIIOSPHOKITE. 231 



ori<2:inal substance witli a solution of ammonic carbonate. 



evaj^orate the mixture very carefully to dryness in a cov- 

 ered crucible, repeat the operation several times, and ig- 

 nite, finally, to a dull red heat, not strong enough to burn 

 the coal. Determine carbonic acid in this residue ; the 

 difference between the quantity found here and in c repre- 

 sents an equivalent quantity of calcic hydrate or caustic 

 lime, CaO, H^O. 



B. Bone-ash should be treated as directed for the ash 

 of bone-meal, with tire addition of determinations of 

 moisture and of carbonic acid, for the purpose of estimat- 

 ing the calcic carbonate. 



C. Phosphorite, coproUtes. — Phosphorite, nnd other 

 minerals containing phosphoric acid, are usually mixed 

 with oxides of iron and alumina to such an extent that 

 the acid cannot be determined volumetrically. 



a. Phosphoric acid, — To determine this alone, Freseni- 

 us gives the following directions. {Fresenius'^ s Zeitschrlft^ 

 6, 404). 



Heat about 0.5 grm. of the finely pulverized mineral in 

 a small flask about an hour on the water-bath, with 8-10 

 c.c. of concentrated (fuming) hydrochloric acid, aud 

 evaporate the mixture to dryness in the usual manner for 

 eliminating silica (§ 58, a^ 1 ) ; moisten the residue with 2 

 c.c. of hydrochloric acid, add, after a short time, 10 c.c. 

 of concentrated nitric acid (Sp. Gr. 1.2), dilute Avith 

 Avater, filter and wash the insoluble residue ; evaporate the 

 filtrate and washings almost to dryness, dissolve the resi- 

 due in 5 c.c. of nitric acid, transfer the solution to- a beak- 

 er, rinse out the evaporating dish with a little water, and 

 then with the solution of ammonic molybdate ; add, in 

 all, 150-200 c.c. of this reagent, and proceed with the 

 elimination of the acid as directed in § 61, h. 



h. Complete analysis. — ^Digest 5-10 grms. of the well- 

 pulverized mineral with hydrochloric acid, filter out the 



