pyrogallic, a. Chem.
(ˌpaɪərəʊˈgælɪk)
[f. pyro- 3 + gallic a.2]
Produced from gallic acid by the action of heat: in pyrogallic acid, an acid substance, C6H6O3 (strictly a trihydric phenol, C6H3(OH)3, hence systematically named pyrogallol), which crystallizes in long flat colourless prisms, soluble in water; much used as a reducing agent in photography (see pyro) and otherwise. Hence pyrogallic developer, etc.
| 1836 Brande Man. Chem. (ed. 4) 933 Pyrogallic acid has been analyzed by Berzelius under the name of gallic acid. 1838 T. Thomson Chem. Org. Bodies 86 Braconnot..showed that when gallic acid is sublimed, it is converted into a substance possessing quite different properties... He therefore gave it the name of pyrogallic acid. 1856 E. A. Hadow in Orr's Circ. Sci., Pract. Chem. 194 After the pyrogallic solution has apparently done its utmost. 1861 Photogr. News Alm. in Circ. Sc. (c 1865) I. 160/1 There are two methods of development; with pyrogallic acid and with gallic acid. 1869 Roscoe Elem. Chem. 417 On heating, gallic acid splits up into carbon dioxide and pyro-gallic acid or trihydroxyl benzol. 1878 Abney Photogr. (1881) 103 A pyrogallic-acid developer. |
Hence
pyroˈgallate, a salt of pyrogallic acid;
pyroˈgallein, a product of the action of air on an ammoniacal solution of pyrogallic acid;
† pyroˈgallin (
rare),
pyroˈgallol, synonyms of pyrogallic acid.
| 1836 Brande Man. Chem. (ed. 4) 933 Ammonia, soda, and potassa, form soluble *pyrogallates. 1878 Abney Photogr. (1881) 98 The alkaline pyrogallates have..an affinity for the halogens. |
| 1866–8 Watts Dict. Chem. IV. 758 *Pyro⁓galleïn, an uncrystallisable product. |
| 1876 Harley Mat. Med. (ed. 6) 422 Heated to 410°, gallic acid is..converted into *pyro-gallin and carbonic anhydride. |
| 1876 Encycl. Brit. V. 564/2 Trihydric phenols comprising..pyrogallic acid (or *pyrogallol). 1899 Allbutt's Syst. Med. VIII. 580 The remedies..found most useful are tar, chrysarobin, and pyrogallol. |