10 



ON THE UNION OF TAN AND JELLT. 



dual fluids precipitated jelly, proving that they contained a 

 quantity of uncombined tan ; but the precipitation was of 

 course much \ess copious in the one which had received the 

 smallest quantity of jelly. The weights of the precipitates 

 were to each other in the ratio of 16, p/5, and 7. As in all 

 the cases the whole of the jelly had entered into combina- 

 tion, the proportion of the jelly to the tan might be esti- 

 mated. In the first experiment, i. e. where 8 parts of jelly 

 and 10 of tan were employed, the jelly and tan in the com- 

 pound were nearly equal ; where 4 parts of jelly had been 

 added to ]0 of the rhatany, the proportion in the compound 

 Was as 42 to 58 ; and where only 2 parts of jelly had been 

 employed, the compound consisted of 28*5 parts of jelly to 

 71*5 of rhatany. From these experiments we learn, that in 

 proportion as the tan exists in excess more of it becomes 

 When the tan united to the jelly ; so that if we were to attempt to esti- 



is in excess, ma t© the amount of the jelly in any fluid by the weight of 



more unnes .... 



■with the jelly, the compound which it forms with tan, we fhould much 



overrate the quantity of the jelly. Having found, that, 

 where the solutions are employed in a state of considerable 

 concentration, a compound is formed consisting of nearly 

 equal weights of the two ingredients, we might conclude, 

 that the quantity of jelly in the third experiment was in the 

 proportion of 3'5, while in fact it was no more than as 2. 

 Differences of ^ ^ e physical properties of the precipitates were consider- 

 the precipi- ably different, so as to indicate a difference in their chemical 

 composition. The first precipitate, which was composed cf 

 nearly equal parts of the two ingredients, was of a dark red 

 colour, of a hard and brittle consistence, and presented a 

 shining fracture. The second was also hard, but rather 

 tough, and it had a" brown hue ; the third, containing the 

 smallest quantity of jelly, was of a bright reddish brown, 

 and could be pulverized between the fingers. In order to 

 establish more clearly the difference between these precipi- 

 tates, the}' were subjected to the action of such reagents as 

 might have the power of removing from them the excess of 

 tan, and leave the compound in its most perfect state. This 

 seemed to be effected by boiling- the third precipitate in a 

 large quantity of water, in consequence of which process the 

 fluid was found to have acquired the property of copiously 



precipitating 



