3 ON THE UNION OF TAN AND JELLY. 



and much water. By permitting glue divided into small pieces to re- 

 water, main in a heat of about 150° for 24 hours, I found that it 

 had lost lOf per cent of its weight. And even although we 

 might have the glue in a state of complete dryness and 

 purity, I should doubt whether it be a proper substance to 

 Glue differs employ on the present occasion. Although it possesses the 

 considerably properties which characterize jelly, yet a solution of glue 

 will be found to differ from a solution of isinglass, while they 

 both contain the same proportion of solid matter. This 

 difference is the most remarkable with respect to their 

 power of concretion. A. solution of glue, which I found by 

 evaporation to contain -J T of its weight of solid matter, al- 

 though strongly adhesive, remained quite fluid when cold, 

 whereas a similar solution of isinglass jelly would have been 

 perfectly concrete. Glue also differs from isinglass in be- 

 ing considerably more soluble in cold water. Glue broken 

 into small pieces, and digested in ten times its weight of 

 water, at the temperau e of the atmosphere, was in 48 

 hours entirely broken down, and so far dissolved, that the 

 upper part of the fluid strongly precipitated the infusion of 

 galls. Pieces of isinglass treated in the same manner were 

 softened, and had their bulk increased, but the fluid, was 

 scarcely affected by tan. These circumstances led me to 

 regard glue as different from isinglass jelly, and as possess- 

 ing in an inferior degree the characteristic properties of 



. jelly. 



Experiments From these different circumstances I determined to em- 

 sojubl^drts 16 PW tne soluble parts of isinglass, and the extract of rhata- 

 of isinglass and ny, in my future experiments on the combination of tan and 

 rhatan jelly. But before I enter upon a description of the results, 



that were obtained b} r the union of these substances, I think 

 it necessary to point out the difficulty, which occurs in the 

 prosecution of these experiments, particularly in the col- 

 lecting of the precipitate. When the tan and jelly are not 

 Difficulty of employed in a state of considerable concentration, and when 

 pred pi'tcue. * they are not added together in that proportion, which seems 

 to form the most perfect compound, the precipitate sepa- 

 rates slowly from the fluid, or sometimes remains perma- 

 nently suspended; and when it is passed through a filter, it 

 adheres to the paper so strongly, that it cannot be com- 

 pletely 



