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°.