150 The Phosphates of America. 



is washed, dried, calcined and weighed as Mg 2 P 2 O 7 , every part 

 of which X .1396 = phosphate of lime (Ca 3 P 2 O 8 ). 



We now refer to our note-book to find the weight of the com- 

 bined phosphate and fluoride of lime contained in the five grammes of 

 the original sample asdeterrnined after the acetic-acid treatment, and 

 by means of this weight we now make the following calculation : 



EXAMPLE (TAKEN AT RANDOM FROM OUR AGENDA). 



Weight of the residue of combined phosphate and fluoride 



of lime in 5 grammes of the sample 3.900 



Weight of the phosphate of lime calculated from Mg 2 P 2 O 7 . 3.775 



Fluoride of lime, by difference in 5 grammes 0.125 



Therefore 5 : .125 : : 100 : x = 2.50 per cent, fluoride of lime, 

 which X .4897 = 1.22 per cent, fluorine. 



Oxides of Iron and Alumina. 



This highly-important determination is the object of much con- 

 troversy, and may be roughly said to be the pivot upon which 

 revolves very nearly every difference in the phosphate analyses of 

 various chemists. A large number of schemes have been devised 

 and experimented with, but only very few of them have proved 

 worthy of general application. 



The chief points required of a method for practical work are : 

 that it should be accurate, that it should be easy and rapid, and 

 finally, that it should be economical. All these we believe to be 

 embodied in the following plan, which, when carried out with care 

 and exactly as we shall describe it, produces constant and strictly 

 concordant results. When left to our own choice we have always 

 preferred it to any other for our own work, and many of our pupils 

 and former assistants who have left us and are now employed 

 either at phosphate mines or at fertilizer works throughout the 

 country, continue to exactly accord in results with our laboratory. 

 We consider this to be a great point in its favor, and it is in fact 

 the one which mainly prompts us to so strongly recommend its 

 general adoption. 



Fifty c.c. of the filtrate from the siliceous matter, equalling one 

 gramme of the phosphate, are placed in a beaker and made alkaline 

 with ammonia. 



The resulting precipitate is redissolved by the addition of just 

 sufficient hydrochloric acid, and the liquid is then again made 

 alkaline with ammonia in very slight excess. Fifty c.c". of concen- 

 trated and pure acetic acid are now added ; the mixture is stirred, 



