38 JOURNAL OF THE 



then 



.^_= no of pounds acid used needed to render i pound phosplioric acid soluble. 



y 



and 



zx 

 p = m. 



y 



The coefficient of solubility is given by the formula c— ^- 



zx 



It is evident that some starting point is required, and for this it 

 is most convenient to take SS'^B., and to consider that the reaction 

 given on p. 35 of this article is the true one, viz. : Ca.jP^OgH- 

 2HoS04 = CaH4P20s+2CaS04. A stronger acid than 53°B is very 

 seldom used in the manufacture of acid piiosphates, and t is custo- 

 mary to say that two parts by weight of 53^B acid will completely 

 decompose one part of bone phosphate. Of course c. will vary with 

 the strength of acid used, for instance it will vary from .23 in 53°B 

 acid to .19 in 46°B acid. It is perhaps needless for me to say there 

 are many causes operating to prevent the universal application of 

 these working formulae. Foremost among these is the variation in 

 the composition of the crude rock whereby compounds of phospho- 

 ric acid other than Tri-calcium Phosphate may exist. Then comes 

 the variation in the fineness of the rock when the acid is added to 

 it. This is a point of far greater importance than is generally sup- 

 posed, and upon it depends in very large measure the quality of the 

 resulting acid phosphate. It has been shown by a writer in Lippin- 

 cott's Encyclopaedia of Chemistry, vol. 2, p. 375, art. "manure," 

 that in the case of Navassa Phosphate, there was obtained 



from dust that passed a 38^ seive 22.65 per cent, soluble phosphate. 

 " " 50 " 23.80 " 

 " as fine as possible, 25.75 " " " " 



And he goes on to say, " No dust should be used which does not 

 pass through a seive of 40 wires to the inch, and in the case of hard 

 phosphates, still finer grinding is very desirable." If he had said 

 that all the dust should pass a 60^^ seive, he would have been still 

 nearer the truth. 



Variation in the purity of the acid used is also a very important 

 factor. It is well known that the strength of the acid, as given by 

 Beaume's Hydrometer, is not always correct, when the chamber 

 acid is employed, as the dissolved impurities cause a higher reading 

 than the amount of acid justifies. The humidity of the atmosphere 



