76 CHEMICAL MANUEES. 



Now as 92-2 parts of H.^SO^ contain 51-6 parts of SO3, 100' 



. 51*6 X 100 ^r f^n rir\ t • i > • -i 



parts contain — qt^-t = 00 'yb SO3. It is, therefore, acid con- 



taining 56 per cent of SO3 that has to be used. By consulting the 

 table by Lunge and Isler, at the end of the book, it will be found 

 that acid of that strength has the specific gravity of 1-600 = 54"" B. 

 or 120° Twaddel. But in actual practice it happens that the acid 

 used is more concentrated or more dilute. Suppose that the acid 

 marked 60^ B., according to the table above mentioned, contains 63-7 



per cent SO3, it will, therefore, be necessary to use — ^^-^ = 81 



Do ' I 



parts to render 100 parts of tribasic phosphate of lime soluble, and 

 it would be necessary to add the required amount of water thereto. 

 If the acid weighs less than 54° B., say 50° B., the same calculation 

 is made. Acid of 50° B. contains 51 'Ol per cent SO3 of acid of that. 



strength, therefore it would be necessary to use ^^ ^, — = 101 

 » -^ 51-04 



parts for 100 of Ca3P.O.,. 



Effect of the Impurities in Phospliates on their Beliaviour in 

 the Process by which they are Rendered Soluble. — But raw phos- 

 phates, moreover, contain several other compounds besides tribasic 

 phosphate of lime — such as carbonate of lime, oxides of iron, and 

 alumina, calcium fluoride, decomposable silicates, etc. If, therefore, 

 only the amount of sulphuric acid required for the phosphate were 

 taken, the latter would not be rendered completely soluble, because 

 the sulphuric acid would first attack the carbonate of lime and then 

 the tricalcic phosphate. It is thus necessary to determine the 

 percentage of these ingredients in the phosphate and allow for them 

 in calculating the acid. 



Carbonates of Lime and Magnesia. — In treating phosphates 

 with sulphuric acid, the carbonates are attacked first. It is 

 generally a question of carbonate of lime, as carbonate of magnesia 

 is only met with rarely, for example in Carolina and Florida phos- 

 phates. Carbonate of lime is, therefore, dissolved at the very first, 

 then follow the other compounds in the order of their decomposa- 

 bility by acid. The decomposition of the carbonate of lime and the 

 consequent formation of gypsum which follows it at an equal pace, 

 causes an energetic reaction, which is very favourable to the 

 progress of the process by which the phosphates are rendered 

 soluble. The heat disengaged re-heats the mass, the carbonic acid, 

 in its efforts to escape raises the mixture and renders it porous and 

 spongy like a well-risen loaf in the baker's oven, and thus facilitates 

 drying. More than 5 per cent of carbonate acts unfavourably, in 

 this sense that leaving the expense of the extra acid ^ that it entails 



^ But the acid is the raw material on which the manufacturer makes his. 

 profit !— Tr. 



