ON THE UNION OF TAN AND JELLT. J 



proportion to the strength of the solution, either of jelly or 

 of tan, will be the weight of the precipitate obtained*. It 

 would appear, that, when the solutions are much diluted, 

 the attraction of both the jelly and the tan for the water, 

 to a certain extent, counteracts their attraction to each 

 other, and thus prevents a portion of them from being re- 

 moved from the fluid. Mr. Davy, however, as well as Mr. Both suppose 

 Biffo-in, evidently seems to have conceived, that the sub- th fi ;reci * tatd 

 stance which was precipitated in all instances possessed the compound. 

 same properties, and consisted of a uniform compound of 

 the two ingredients. This opinion is the very foundation of 

 the method which he employed in his analyses, and is di- 

 rectly asserted in different parts of his papers f. 



With this impression it was, that I entered upon a set of The author's 



f . «iii r proceeding th* 



experiments, which may be considered as the converse ot conve rseof 

 those of Mr. Biggin and Mr. Davy. The object of these theirs « 

 chemists was, by the agency of jelly, to remove all the tan 

 from a vegetable infusion, and to estimate its quantity from 

 the weight of the precipitate; while mine was, by means of 

 tan, to ascertain the quantity of jelly that was contained in 

 any animal fluid. In pursuing this investigation, the first a uniform re- 

 point was to determine upon the most proper substance to a S ent requisite. 

 employ as the reagent ; for as it is difficult, if not absolutely 

 impossible, to procure tan in a state of perfect purity, it 

 became necessary to discover some vegetable infusion, which, 

 should always possess similar properties, and in which the 

 quantity of tan should be known, without having recourse 

 to any long calculation. My attention was naturally, in 

 the first instance, directed to galls; and I expected, that Galls, 

 by employing equal weights, infusing them in equal quan- 

 tities of water, and for an equal length of time, fluids 

 would have been formed always containing equal quantities 

 of tan. But upon making repeated trials, I find that this 

 is not the case; and it would appear from all the experience Not uniform ia 

 I have had upon the subject, that two parcels of galls will their natur9 » 

 scarcely ever be procured, which will precisely agree in their 



* Phil. Trans. 1803. 



t Phil. Trans. 1803. Nicholson's Journal, vol. V, p. 259, 269, St 

 alibi. 



B 2, nature. 



