158 The Pliospliates of America. 



It follows, therefore, that if a solution of phosphoric anhydride 

 in acetic acid, be treated with a solution of uranic acetate, the P 2 O 5 

 is precipitated, and it has been found that the slightest excess of 

 uranic acetate can be detected in the mixture, by bringing a drop 

 of it into contact with a drop of freshly-prepared solution of potas- 

 sium-ferrocyanide, and noting the reddish -brown color produced. 

 The first step being to establish the accuracy of the solutions, 50 

 c.c. of the standard solution of sodic phosphate are run into a 

 small beaker; made akaline with ammonia; and then distinctly acid 

 with acetic acid. Five c.c. of the sodic-acetate solution are now 

 run into the mixture with a pipette ; the beaker is brought over 

 the flame of a Bunsen burner and the contents heated to about 70 

 C. When this point is attained the uranic-acetate solution is run 

 in very cautiously, drop by drop, from a burette, until a drop of 

 the mixture in the beaker taken out and placed in contact with a 

 drop of the ferrocyanide solution, on a white porcelain slab or plate,, 

 gives a slight, but yet distinct, reddish-brown color. 



When the necessary point has been attained which generally 

 requires two or three trials the uranic solution is so arranged by 

 dilution, or calculation, as to make 1 c.c. of it correspond to ex- 

 actly 1 c.c. of the standard sodic-phosphate solution ; in other 

 words, to .002 P 2 O 5 . 



The accurate standardization being completed, the sample of 

 mineral phosphate to be examined is now weighed out. One gramme 

 is dissolved in nitric or hydrochloric acid in the usual way, and 

 with the usual precautions is filtered and washed to about 200 c.c. 

 Fifty c.c. (equal to .250 gramme phosphate) are now placed in a 

 beaker, made alkaline w r ith ammonia, then strongly acid with acetic 

 acid and treated with 5 c.c. of sodium-acetate solution. The mixt- 

 ure is then heated to 70 C., and at this temperature the uranium 

 solution is run in, drop by drop, until the color reaction on the 

 white plate is plainly visible. A second titration is made on an- 

 other 50 c.c. of the solution of phosphate, and if the results are the 

 same the operation is ended. Every c.c. of the uranic-acetate 

 solution used equals .002 gramme P 2 O 5 in .250 gramme of the 

 material. 



As will have been gathered from our opening remarks, the re- 

 sults of this process, as w r e describe it, are seriously vitiated by 

 the presence of more than one per cent, of iron and alumina. 

 When, however, these two bodies are present in any considerable 

 amount there is a way out of the difficulty afforded by the fact 



