on the constituent Parts of astringent Vegetables. 235 
the quantity of the precipitate obtained by filtration, is not always 
exactly proportional to the quantities of tannin and gelatine in 
solutions, but is influenced by the degree of their concentration. 
Thus, 1 found that 10 grains of dry isinglass, dissolved in two 
ounces of distilled water, gave, with solution of galls in ex- 
cess, a precipitate weighing, when dry, 17 grains; whilst the 
same quantity, dissolved in six ounces of water, produced, ail 
other circumstances being similar, not quite 15 grains. With 
more diluted solutions, the loss was still greater ; and analogous 
elfects took place, when equal portions of the same solution of 
isinglass were acted on by equal portions of the same infusion 
of galls diluted in different degrees with water; the least 
quantity of precipitate being always produced by the least con- 
centrated liquor. In all cases, when the weak solutions were 
used, it was observed, that the residual fluid, though passed two 
or three times through the filtre, still remained more or less 
turbid and opaque ; so that it is most likely that the deficiency 
arose from the continued suspension of some of the minutely 
divided solid matter in the liquid mass. 
The solutions of gelatine, for the purposes of analysis, should 
be employed only when quite fresh, and in as high a state of 
saturation as is compatible with their perfect fluidity. I have 
observed, that in cases when they approach towards the state of 
jelly, their power of acting upon tannin is materially altered, 
and they produce only a very slight precipitation. As the de- 
gree of fluidity of solutions of gelatine is influenced by their 
temperature, I have found it expedient, in all comparative ex- 
periments, to bring them and the astringent infusions on which 
they are designed to act, as nearly as possible to a common 
degree of heat. My standard temperature has been between 6'o 
H h 2 
