246 ON VEGETABLE ASTRINGENTS. 



siohs which I formed to he slightly reddened by litmus. 



After the infusions of catechu have undergone tne operation 



of moulding, they are much less afTeefed both by jelly and 



by the oximuriate of tin, but I never carried the process 



so far as to observe whether they could be entirely deprived 



of the capacity of being acted on by these reagents. 



Unsuccessful According to Mr. Davy's observations the separation of 



attempts to se- , , *' 



p ara , ethe tan the tan and extract or catchu may be accomplished with a 



and extract of considerable degree of accuracy, and he points out three 

 different ways in which this may be effected. Tan, he rer 

 marks, is more soluble in water than extract, if therefore 

 catechu be subjected for a short time to a small quantity of 

 water, the tan alone will be dissolved, and the residue will 

 contain a greater proportion of extract. 1 infused a portion 

 of catechu for a few minutes in about ten times its weight 

 of water, by which a part only was dissolved. The residue 

 was afterward dissolved by the addition of more water, and 

 when each of the infusions was become clear, by depositing 

 a part of their conten s, they were both of them submitted 

 to the action of jjelly and the oximuriate of tin ; the first im- 

 fusion was stronger, but I could not observe the least dif- 

 ference in the proportional effects of the two reagents. Mr, 

 Davy's 2d method of separating tan from extract is found- 

 ed upon the principle, that extract is more soluble in warm 

 than in cold water, and therefore if a saturated warm infu- 

 sion be formed, when it cools the tan will remain dissolved a 

 while the greatest part of the extract will be deposited. J 

 put this process into execution, but upon applying the two 

 reagents they both seemed to act in an equal degree, dif- 

 fering only in their effects in consequence of the matter 

 Avhicb was deposited being rather less soluble than the en- 

 tire catechu. The 3d method of separating the tan from 

 the extract is by forming a number of successive infusions, 

 when it is said, that the tan will become first exhausted, 

 and the extract be left in u state of almost perfect purity. 

 I have already related the result of this operation, which was 

 not at all comfprmable to the above statement. These cir- 

 cumstances I regard as amounting to a positive proof of an 

 essential difference between tlie substances, which were em- 

 ployed by Mr. Davy aud myself. 



In 



