238 Mr. Davy’s Experiments and Observations 
action upon extractive matter. I have been able, in examining 
solutions of galls, to separate a portion of gallic acid by 
means of ether. But, when the extractive matter is in large 
quantities, this method 'does not succeed, as, in consequence of 
that affinity which is connected with mass,* the greatest part of 
the acid continues to adhere to the extract. 
Alumine has a strong attraction for extractive matter; but 
comparatively a weak one for gallic acid.-f When carbonate of 
alumine is boiled for some time with a solution containing ex- 
tractive matter, the extractive matter is wholly taken up by the 
earth, with which it forms an insoluble compound; but, into 
this compound, some of the gallic acid appears likewise to enter ; 
and the portion remaining dissolved in the solution is always 
combined with alumine. 
I have not, in any instance, been able to separate gallic acid 
and extractive matter perfectly from each other; but I have 
generally endeavoured to form some judgment concerning their 
relative proportions, by means of the action of the salts of alu- 
mine, and the oxygenated salts of iron. Muriate of alumine 
precipitates much of the extractive matter from solutions, without 
acting materially upon gallic acid ; and, after this precipitation, 
some idea may be formed concerning the quantity of the gallic 
acid, by the colour it gives with the oxygenated sulphate of iron. 
In this process, however, great care must be taken not to add 
the solution of the sulphate of iron in excess ; for, in this case, 
the black precipitate formed with the gallic acid will be redis- 
solved, and a clear olive-coloured fluid only will be obtained. 
* See Berthollet, Richer ches sur les Lois ds VAfflnite . Mem. cle VInstitut Na- 
tional. Tome I! I. p. 5. 
f See Fiedler, Journal de Cbimie, par j. B. Van-mons, Tome I. pag. 85. 
