The Phosphates of America. 



Phosphoric anhydride (P 8 O 5 ). 72.45 



Water (H 3 O) 27.55 



100 



And it may be regarded as typical of the tribasic combination 

 in which the anhydride is always encountered in nature. 



It has the faculty of exchanging one, two, or all three of its 

 water-molecules, for molecules of vari9us bases, and thus we are 

 quite familiar with it as 



CaO(H 2 O) 2 P 2 O 6 , or acid phosphate of lime, in which it has 

 taken one molecule of lime in place of one molecule of water ; 



(CaO) 2 H 2 O P 2 O 5 , or neutral phosphate of lime, in which it 

 has taken two molecules of lime in place of two molecules of 

 water ; and 



(CaO) 3 P 2 O 5 , or tribasic phosphate of lime, in which all the 

 water-molecules have been displaced by lime. 



The first of these compounds is soluble in water. 



The second insoluble in water but soluble in neutral citrate of 

 ammonia. 



The third is only soluble in strong acids. 



When quite pure, every 100 parts of each of them is made 

 up of 



The tricalcic or last of these compounds is the phosphate of 

 lime which occurs in the deposits we have been engaged in con- 

 sidering, and the problem of making it soluble in water or in 

 neutral citrate of ammonia has been worked out by chemists on 

 the following basis : 



Sulphuric acid is known to be more energetic in its action at 

 ordinary temperatures than any other acid used in industry. It 

 therefore has the power of displacing all other acids from their 

 salts arid of taking their bases to itself to form sulphates. 



The acids chiefly present in natural phosphates are phosphoric, 

 carbonic, fluoric and silicic, and these, when brought into contact 



