2£o Mr. Davy’s Experiments and Observations 
conclude, that, in the case of the precipitation of tannin by the 
salts of tin and of iron, compounds are formed, of tannin and 
the salts ; and that, of these compounds, such as contain tin are 
slightly soluble in water, whilst those that contain iron are 
almost wholly insoluble.' 
In examining the action of animal substances upon the infu- 
sion of galls, with the view of ascertaining the composition of 
the compounds of gelatine, and of skin, with tannin, I found that 
a saturated solution of gelatine, which contained the soluble 
matter of 50 grains of dry isinglass, produced from the infusion 
a precipitate that weighed nearly 91 grains ; and, in another 
instance, a solution containing 30 grains of isinglass, gave about 
5b grains; so that, taking the mean of the two experiments, 
and allowing for the small quantity of insoluble matter in 
isinglass, we may conclude, that 100 grains of the compound of 
gelatine and tannin, formed by precipitation from saturated 
solutions, contain about 34 grains of gelatine, and 4 6 of tannin. 
A piece of dry calf-skin, perfectly free from extraneous matter, 
that weighed 180 grains, after being prepared for tanning by 
long immersion in water, was tanned in a portion of the infu- 
sion, being exposed to it for three weeks. When dry, the leather 
weighed 295 grains : so that, considering this experiment as 
accurate, leather quickly tanned by means of an infusion of 
galls, consists of about 61 grains of skin, and 39 of vegetable 
matter, in 100 grains. 
After depriving a portion of the infusion of all its tanning 
matter, by repeatedly exposing it to the action of pieces of skin, 
I found that it gave a much slighter colour to oxygenated sul- 
phate of iron, than an equal portion of a similar infusion which 
had been immediately precipitated by solution of isinglass; 
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