ON THE UNION OF TAN AND JELLY. Q 



pletely removed from it. Nor could I obviate this objection 

 by weighing the paper before and after the fluid had pass- 

 ed through it, and thus calculating the weight of the preci- 

 pitate. I found that in this case the paper acquired weight, 

 not only from the precipitated matter, but likewise from 

 what was still retained in solution. When an infusion of 

 rhatany in the proportion of 1 to 10 was passed through a 

 paper filter, the filter when dried was found to have acquir- 

 ed an addition of not less than r \ of its former weight. A 

 solution of jelly of the same strength passed with difficulty 

 through the paper, and a large part was detained by it. 

 Hence it follows, that, except in those cases where the fluids 

 neutralize each other, so as to precipitate all their contents, 

 we cannot ascertain the amount of the precipitate from the 

 weight gained by the filter. What has been said will be 

 sufficient to {how, that perfect accuracy cannot be attained 

 in these processes, even were the compound of tan and jelly 

 in all cases a uniform substance. 



I was soon however convinced, that the substance formed The preclpi- 



by the union of tan and jelly varies considerably according' ta,e not uni * 



... form. 



to the circumstances under which it is formed, particularly 



according to the proportion in which the two ingredients are 

 presented to each other. Without entering into a detail of 

 the numerous trials, that I made upon this subject, I 

 {hall think it sufficient to give an account of one expe- 

 riment, that may serve as a specimen of the rest. I must 

 here remark, that, although my experiments agreed suffi- 

 ciently to satisfy me respecting the nature of the conclusions 

 that were to be deduced from them, yet I never performed 

 two, in which the results exactly coincided. 



Three equal portions of the extract of rhatanv were dis- n 



n T 7 Experiment. 



solved in ten times their weight ot water; and three por- 

 tions of jelly from isinglass were procured, bearing respec- 

 tively the proportions of 8, 4, and 2 to the* three portions of 

 rhatany. These were also dissolved in equal quantities of 

 water, kept soluble by heat, and added to the three portions 

 of rhatany. Copious precipitates were produced in all of 

 them, and after standing for some time, the supernatant 

 fluids became clear. Tne precipitates were collected and 

 dried by exposure to the same degree of heat. All the resi- 

 dual 



