CONVERSION OF TANNIC INTO GALLIC ACID. 113 
no longer coloured by persalts of iron. Of the different 
substances examined, sulphuric acid appeared to effect the 
conversion of the tannic acid best. If 50 grms. of dry 
tannic acid are heated to boiling in a mixture consisting of 
100 cubic centimetres sulphuric acid of 1.84 spec. grav. and 
400 cubic centimetres water, there will be found in the 
course of a few days an abundant precipitate of very white 
gallic acid. Once, on employing this process, the sulphuric 
acid was removed by means of carbonate of baryta, the 
liquid filtered, evaporated to dryness, weighed, treated with 
ether, and again weighed, and the solution acidified with 
acetic acid, treated with basic acetate of lead. This last 
precipitate was well washed and decomposed with sulphu- 
retted hydrogen, after which the filtered solution was 
treated as above. In the first treatment, 12 per cent, of a 
substance insoluble in ether was obtained, which consisted 
principally of gallate of baryta, and of 1 to 2 per cent, of a 
black body, which was probably an impurity in the tannic 
acid. The precipitated sulphate of lead, and likewise the 
sulphate of baryta, also parted with gallic acid to nitric 
acid ; but excepting the above mentioned black substance, 
nothing further could be detected ; and it therefore appears 
that the entire amount of tannic acid was in the above 
manner converted completely into gallic acid. Lime might 
be substituted for the baryta with the same result. The 
maximum quantity of gallic acid obtained amounted to 
87.4 per cent, of the tannic acid. In an analysis of tannic 
acid, the author arrived at the generally admitted formula 
CisH^O^^; it yielded 50.63 carbon, 3.64 hydrogen, and 
45.73 oxygen. Wackenroder and Larocque have stated 
that this conversion may also be effected by ferments^ 
albumen, blood, and a substance capable of fermentation 
in gall-nuts ; and Humfeld found that tannic acid was 
destroyed without the formation of gallic acid, by the action 
of oxidising agents, such as manganese, chromic acid, per- 
oxide of mercury, &c. If the results of the analyses of 
