Q ON THE UNION OF TAN AND JELLY. 



solutions of catechu, a portion appeared to be only sus- 

 pended in the fluid, so that it remained muddy, and neither 

 became transparent by standing, nor was the insoluble part 

 Spontaneous removed by passing through a filter. The infusions of ea- 

 decomposition likewise became altered by exposure to the atrno- 



sphere more rapidly than those of galls, a considerable 

 portion of the substance that had been dissolved being 

 gradually deposited. This deposition goes on so rapidly, 

 as to exhibit an appearance something similar to the 

 saline vegetation of certain salts, the catechu creeping up 

 along the sides of the glass to some distance above the 

 surface of the fluid. I was not able 10 detect any dif- 

 ference between the part of the catechu which is retained 

 in solution, and that which, is deposited, except that the last 

 was of a lighter colour, and was less soluble in water; they 

 both produced precipitates with jelly and the muriate of 

 Its precipitate tm# ^'he Precipitate which the catechu forms with jelly, 

 like that of ar- like that produced by the artificial tan, does not in general 

 form a compact or solid mass, but makes the fluid turbid 

 without entirely subsiding from it, nor is it rendered trans- 

 parent by being passed through a filter. This circumstance, 

 as well as its imperfect solubility, renders catechu inappli- 

 cable as a test for jelly. 

 Extract of rha- The next substance that I tried was the extract of rha- 

 **"?• tany, a preparation said to be brought from the Portuguese 



settlements in South America ; and, in consequence of its 

 tonic quality, lately proposed as an addition to the materia 

 medica. It contains a large proportion of tan ; from the 

 experiments that I have made upon it, larger than any 

 other astringent extract with which we are acquainted; it 

 appears to be more homogeneous in its consistence, it is 

 completely soluble in water, and seems to remove jelly 

 from its solution more readily than the other substances 

 ■which I had tried. These properties pointed it out as the 

 most nearly approaching to what I was in search of. 

 Preparation pf Before giving an account of the result of the union of tan 

 the jelly. and jelly, it will be necessary to make some remarks upon 



the preparations of this latter substance. It has been stated 

 upon the higliest authority, that of Mr. Iiatchett and Mr. 



Davy, 



