160 The Phosphates of America. 



weight of the pyrites, and watch-glasses, represents the moisture in 

 the sample. 



Siliceous Matter and Silicates. 



One gramme of the original sample is treated with about 20 

 c.c. of a mixture of three vols. nitric acid (specific gravity 1.4) 

 and one vol. strong hydrochloric acid, both ascertained to be 

 absolutely free from sulphuric acid. All spurting is carefully 

 avoided and heat is gently applied, and the mixture evaporated 

 to dry ness in a water-bath ; 5 c.c. of hydrochloric acid are 

 now added, and once more evaporated (no nitrous fumes ought 

 to escape now), and finally the dried residue is treated with a 

 little concentrated hydrochloric acid and 100 c.c. of hot water 

 and filtered through a small filter and washed with hot water. 

 The insoluble residue on the filter is dried, ignited and weighed. 

 It may contain besides silicic acid and silicates some sulphates 

 of barium, lead and calcium, but these may be disregarded. 



Sulphur. 



The filtrate and washings from the last determination, are 

 slightly saturated with ammonia, filtered while hot, and washed on 

 the filter with hot water, avoiding channels in the mass. Suffi- 

 ciently dense, but yet rapidly-filtering paper, must be used, and 

 -choice made of funnels with an angle of exactly 60, whose tube is 

 not too wide, and is completely filled by the liquid running 

 through. The washing is continued until the addition of a little 

 Bad 2 to the last runnings shows no opalescence even after a 

 few minutes. The filtrate and washings must not exceed 200 c.c., 

 or if they do, they should be concentrated by evaporation. Pure 

 HC1 in very slight excess is now added ; the liquid is heated to 

 boiling ; removed from the burner ; and treated with 40 c.c. of 

 & ten-per-cent. solution of BaCl 2 , previously heated to boiling. 

 After precipitation the liquid is left to stand for half an hour, 

 when the precipitate should be completely settled. The clear 

 portion is decanted through a filter, and the precipitate is washed 

 with hot water by decantation three or four times, until the liquid 

 loses all acid reaction. It should then be washed on to the filter, 

 dried, ignited and weighed. Its weight X .1372 = sulphur in one 



gramme of the ore. 



Iron. 



The ferric hydrate, precipitated from the original solution in 

 the sulphur determination, is dissolved in dilute sulphuric acid, 



