16 Experiments and Observations 
and muriatic acid decompose the phosphates in 
the same manner as sulphuric acid. Only it 
happens in their case that the new com- 
pound (for instance, nitrate or muriate of 
lime) is soluble; whereas, sulphate of lime 
is not soluble, and hence a visible effect of 
decomposition is exhibited. But there is 
sufficient proof to be found that when nitric 
acid acts on phosphate of lime, it decom- 
poses the phosphate, unites with the lime 
and turns afloat a part of the phosphoric acid 
which unites to another part of the phosphate 
of lime and forms with it a superphosphate, 
soluble in the liquor. So that when phosphate 
of lime is dissolved in a minimum of nitric 
acid, the liquor contains nitrate of lime and 
triphosphate of lime in solution. If phos- 
phate of magnesia, instead of lime, is the 
subject, then even sulphuric acid dissolves it 
(in the same way as nitric), and lime water 
and ammonia precipitate the phosphate of 
magnesia unchanged. The reason of this 
apparent difference is, that sulphate of magne- 
sia, the new compound, is a soluble salt, and 
hence no visible decomposition is effected.* 
October, 1817. 
*IT is now nearly 5 years since the above essay was read, 
and since I have made any train of experiments with a view 
fo investigate the phosphates. In this period other che- 
mists have published results of their labour on this subject, 
