Phenyl salicylate, C6H4(OH) C 02C6H5, or salol, is obtained by heating salicylic acid, phenol and phosphorus oxychloride to 120-125° C.; by heating salicylic acid to 2 =0° C.; or by heating salicyl metaphosphoric acid and phenol to 140-150° C. (German Patent 85,565).
This view, which was specially supported by Gay-Lussac and Leopold Gmelin and accepted by Berzelius, necessitated that all acids were monobasic. The untenability of this theory was proved by Thomas Graham's investigation of the phosphoric acids; for he then showed that the ortho- (ordinary), pyroand metaphosphoric acids contained respectively 3, 2 and I molecules of " basic water " (which were replaceable by metallic oxides) and one molecule of phosphoric oxide, P2 05.
As stated under Phosphorus, phosphoric oxide, P 2 0 5, combines with water in three proportions to form H 2 O P 2 0 5 or HP03, metaphosphoric acid; 2H 2 O P 2 0 5 or H4P207, pyrophosphoric acid; and 3H 2 O P 2 0 5 or H 3 PO 4, orthophosphoric or ordinary phosphoric acid.
On long heating the syrup is partially converted into pyrophosphoric and metaphosphoric acids, but on adding water and boiling the ortho-acid is re-formed.
It may be obtained as a glassy mass, indistinguishable from metaphosphoric acid, by heating phosphoric acid to 215°.
Metaphosphoric acid, HP0 3, is a monobasic acid which may be regarded as derived from orthophosphoric acid by the abstraction of one molecule of water, thus H 3 PO 4 - H 2 O = HP0 3; its constitution is therefore (HO)P0 2.
Metaphosphoric acid can be distinguished from the other two acids by its power of coagulating albumen, and by not being precipitated by mag nesium and ammonium chlorides in the presence of ammonia.
It crystallizes in large transparent prisms, which melt on heating and decompose, leaving a residue of metaphosphoric acid, (HP03).
The chemical reactions are as follows: the treatment of the calcium phosphate with the acid gives phosphoric acid, H 3 PO 4, which at a red heat loses water to give metaphosphoric acid, HP03; this at a white heat reacts with carbon to give hydrogen, carbon monoxide and phosphorus, thus: 2HP06+ 6C= H2 +6CO+P2.
Deliquescent, rectangular tablets of H 4 P 2062H 2 O separate out on concentrating a solution in a vacuum, which on drying further give the acid, which melts at 55°, and decomposes suddenly when heated to 70° into phosphorous and metaphosphoric acids with a certain amount of hydrogen phosphide.
It is a white, infusible, very stable solid, which decomposes water on heating, giving ammonia and metaphosphoric acid, whilst alkalis give an analogous reaction.