The Phosphates of America. 155 



existed in the form of silicates or clay, and, as we have pointed 

 out in the chapter on Florida phosphates, our own experiments 

 have very conclusively proved that in a majority of cases, they 

 really do so exist. They would therefore be to a great extent 

 unacted upon by the dilute chamber acid, used in the manufacture 

 either of superphosphates or phosphoric acid. 



ANALYSIS OF SUPERPHOSPHATES. 



The sample should be well intermixed and properly prepared 

 and passed through a sieve having circular perforations one-twenty- 

 fifth of an inch in diameter, so that separate portions shall accurately 

 represent the substance under examination, without loss or gain of 



moisture. 



Moisture. 



Two grammes are accurately weighed into the watch-glasses 

 and heated for five hours at 100 in a steam-bath. 



Water-soluble Phosphoric Anhydride. 



Five grammes are weighed out into a small beaker ; washed by 

 decantation four or five times with not more than from 20 to 25 c.c. 

 of water, and then rubbed up in the beaker w r ith a rubber-tipped 

 rod to a homogeneous paste, and washed four or five times by 

 decantation with from 20 to 25 c.c. of water each time. These 

 washings are all run through a 9-c.c. No. 589 Schleicher and 

 Schiiell filter into a 500-c.c. flask. The residue is finally trans- 

 ferred to the filter, and washed with water until the flask is filled 

 up to the mark. The flask is now shaken, and 50 c.c. of the clear 

 liquor, equal to -J gramme of superphosphate, are transferred to 

 a beaker, and treated with 150 c.c. of molybdic solution. The 

 mixture is digested at 80 C. for one hour, filtered and washed with 

 water. After testing the filtrate for P 2 O 5 by renewed digestion 

 and addition of more molybdic solution, the precipitate is dissolved 

 on the filter with ammonia and hot water (as described in the anal- 

 ysis of raw phosphate) and washed into a beaker to a bulk of not 

 more than 100 c.c. It is nearly neutralized with hydrochloric acid, 

 cooled, and magnesia mixture is added slowly from a burette (one 

 drop per second), with vigorous stirring. After fifteen minutes 

 '30 c.c. of ammonia solution of density .95 are added, and the whole 

 is allowed to stand for two hours. It is then filtered on an ash- 



