242 °N VEGETABLE ASTRINGENTS. 



and which acts upon them when not in a concentrated state, 

 is the acetate of lead ; but this unfortunately cannot be ap- 

 plied in the present instance, because it is equally affected 

 by tan and the gallic acid. The other tests which 1 found 

 in my former experiments on this subject* to act upon par- 

 ticular varieties of mucilage, such as the nitrate of mer- 

 cury, the oxisuiphate of iron, the nitromuriatc of gold, and 

 silicated potash f, were each of them limited to those varie- 

 ties, and can therefore be of no use in determining the ge- 

 neral question, beside that some of them act upon the 



All mucilages other constituents of galls. There is, however, one pro- 

 insoluble in al- . • 1 • 1 n •, , lu • -•■ 

 , . , P ert y, in •which all mucilages seem to agree, i.e. their in- 

 solubility in alcohol ; and it is upon this property, that Mr. 

 Davy has founded bis operation lor obtaining the mucus of 

 galls in a separate state. 

 There appears I endeavoured to imitate his process, but without success, 

 j° enouiuci- ^ strong infusion of galls had its tan separated by jelly, 

 .. the residual fluid was evaporated, and its solid contents 

 were boiled in alcohol, in order to remove from them any 

 extract or gallic acid. What was left was digested in warm 

 water; a very small quantity of it seemed to be dissolved. 

 and the fluid assumed a light green hue. The acetate of 

 lead threw down a slight precipitate, and left the fluid co- 

 lourless; it was tinged by the oxisuiphate of iron ; tartarised 

 antimony and oxalic acid had no effect upon it ; it was nei- 

 ther acid nor alkaline; being slowly evaporated, a small 

 gray residuum was left, which did not resemble mucilage 

 in any of its physical properties. We come to the same 

 conclusion respecting tiie existence of mucus in galls by 

 digesting a quantity of the powder in successive quantities 



* Nicholson's Journal, XV'III, 28, 



+ I am induced to consider the precipitate which is produced bv the 

 addition of silicated potash to gum arabic, a faci which was first rroiiberl 

 by Dr. Thomson fa,), as depending, not upon the immediate action of 

 sijex upon gum, but upon the lime which enters pretty largely uitq its 

 composition, and which causes oxalic acid to throw down a copious 

 precipitate from it. When silicaed potash is added to the different ve- 

 getable infusions, the same effects seem to ensile as from the employ- 

 ment of the alkali without the silex, 



(aj Chemistry, V, 40. 



of 



