2 ON THE UNION OF TAN AND JELLY. 



before your readers; not merely because T have it in tnf 

 power to state some few facts, that may be considered as an 

 addition to our stock of knowledge, but still more, because 

 I may induce some one more skilful than myself, to point 

 out a method of accomplishing what 1 have hitherto at- 

 tempted without success. 

 Jelly. The substance upon which I first operated, and to which 



I shall principally confine my attention in the present pa- 

 Its characters, per, is jelly; the characteristics of which are its solubility 

 in water, its forming an insoluble compound with tan, and 

 the property which its aqueous solution possesses of con- 

 creting by cold, and being redissolved by the application 

 Inquiry whe- of heat. The problem which I was anxious to solve was, 



ther the preci- wne t ner the compound of tan and icily be uniform, so that 



pitate by tan r / 



be proportion- by saturating the gelatinous part of a solution with tan, 



ate to the anc [ co ll ec ting the precipitate, we may, from its weight, 



quantity pre- , ° r r > j •> . 



sent. (the quantity of tan employed being known) ascertain the 



amount of the jelly previously contained in the fluid. From 

 the experiments that had been performed on the subject, 



Mr. Biggin's particularly those of Mr. Biggin and Mr. Davy, I conceived, 



certain the°pro- tnat tms woulf l be found to be the case. The object of Mr. 



portion of tan. Biggin's experiments was to ascertain the proportion of tan 

 in different barks, for which purpose he formed similar in- 

 fusions of them, and precipitated the tan from each by a 

 solution of glue. He employed the^solution of glue always 

 of the same strength, and by collecting the precipitates, 

 he judged of the quantity of tan that had united itself to 

 the glue, and thus of the proportion of it in the bark*. The 

 experiments are important, as comparing the different barks 

 with each other, and thus ascertaining their respective value 

 as substances to be employed in the manufacture of lea- 

 ther; but it is obvious, that, unless the compound 6f tan 

 and glue be uniform, they do not show the absolute quan- 



Mr. Davy tjty of tan in any given weight of bark. Mr. Davy, in his 



shows the pre- eX p er j men t s on astringent substances, has pointed out, with 

 opuate is pro- l .~ . , 



portionate to his accustomed sagacity, the different effects that are pro- 

 the strength of c ] ucec i \ n the union of solutions of tan and iellv, according 

 the solution. . . , , 



to their degree or concentration ; and has proved, that in 



* Phil. Trans. 1799, p. 260. 



proportion 



