MANUFACTUEE OF SOLUBLE PHOSPHATES. 75 



From the following equation the quantities of sulphuric acid 

 and water required to dissolve a given amount of phosphate may 

 be readily calculated : — 



Ca.(P04)2 + 2HoS0, + oHoO = CaH,(P04)'-^HoO + 2(CaSO,'2H..O) 

 ;:310 196 90 252 844 



-596 596 



In this connexion it will be well to bear in mind that the 

 symbols indicate not only the elements but precise and accurately 

 ■determined quantities. Thus the formula for water (H^O) indicates 

 not only that w^ater is composed of the two elements, hydrogen and 

 oxygen, but also that it results from the combination of one atom 

 of oxygen with two atoms of hydrogen. As the atomic weight 

 of hydrogen = 1, and that of oxygen == 16, it will be at once seen 

 that eighteen of water consists of two of hydrogen and sixteen of 

 ■oxygen. These figures apply just as much to grams as to tons. 

 The following is a similar calculation for phosphates, thus tribasic 

 phosphate of lime contains : — 



Atomic 



Weight. 

 Calcium (Ca) = 40 

 Phosphorus (P) = 31 

 Oxygen (0) = 16 



1. A molecule therefore of Ca^fPOj., weighs : — 



Ca^ = 40 X 3 = 120 

 P^ = 31 X 2 = 62 

 0^ = 16 X 8 = 128 



310 



2. A molecule of sulphuric acid H.,SO^ (H = 1 : S = 32 ; 

 O = 16) = 2 + 32 + 16 X 4 = 98. But tribasic phosphate of lime 

 requires two molecules of sulphuric acid to render it soluble ; we 

 thus get 2 X 98 = 196 of sulphuric acid and 5 x 18 = 90 of water. 

 Sulphuric acid may be calculated as SOy and H.,0, say as the 

 hydrate of sulphuric acid and water. To render the phosphate 

 soluble 5 + 2 = 7 molecules of w^ater are required. It follows, 

 therefore, in order to dissolve 310 parts of tribasic phosphate of 

 lime, that these 310 parts of Ca3(P04)., must be put in contact with 

 160 parts of SO3 and 126 parts of water. One part (say one ton) of 



•Ca.,P.,0^ requires therefore -—^ = 0-516 parts SO., and vvv. = 0--406 



parts water. 



100 X 0-516 = 51-6 paits SO- 

 100 X 0-406 = 40-6 „ H.d 



92-2 a,SOj 



