HISTORY OF THE GALLIC ACID. 65 



Oxigenized muriatic acid browns the solution of gallic acid, and oxigenized 



and an excess deprives it of colour. muriatic ac» . 



' On comparing the difference of the effects ©f these acids, it 



will be easy to appreciate them. 



The sublimed acid has less acidity : it is decomposed by the The sublimed 

 .... ~ . acid compared 



air: ithasnoactiononbarytes, carbonat of ammonia, or munat with thecrys- 



oftin. The precipitate obtained with nitrat of murcury is black- taUized - 



ish, instead of yellow : that with acetat of lead is slight and 



fawn coloured, instead of copious and white. 



Oxigenized muriatic acid browns a transparent and colourless 

 solution of the sublimed acid, while it does not alter the -colour 

 of a solution of the crystallized. 



Lastly the sublimed acid does not constantly produce the same 



colour with sulphat of iron, and does not precipitate glue. 



If it be easy to point out the characters that distingiish these ^ ot easv to ac " 

 ...... J , i • , , • , -a. count for the 



two acids, it is difficult to explain whence their difference arises, differences. 



Mr. Berthollet has justly observed, that Scheele's acid, when 



not purified, contains a great deal of tannin; and that, when 



purified by oxide of tin, it does not percipitate glue. 



As to that of Mr. Richter, I havealready pointed out its ana- 

 logy to Scheel^s: yet both these acids appear to me to differ Sublimed acid 

 from that obtained by sublimation. The latter contains a small ^tifeo'ii * Y °~ 

 quantity of volatile oil, which is combined with it; and which 

 by the action of caloric assumes a character approaching to that 

 of oils rendered resinous. This property may be ascertained by 

 dissolving the sublimed acid either in alcohol, or in ether; for if 

 the liquid be evaporated by rubbing it on the skin, we shall ex- 

 perience an effect similar to that produced by a resin dissolved in 

 alcohol. 



It is not without difficulty, as may be supposed, that we can 

 attain a complete knowledge of the nature of the gallic acid. What is the 

 Does this acid exist in galls already formed ? May we consider salIlc acid i 

 it as a peculiar acid ; or rather is it merely the result of the com- 

 bination of a vegetable acid with tannin, extractive matter, and 

 other substances existing in galls ? These are questions, that yet 

 remains to be solved. I have attempted by a series of experi- 

 ments to add some facts to those that are known; and if they do 

 not yet lead to a complete solution I conceive some new results 

 will be found in them, which serve to explain the nature and pro- 

 perties of the gallic acid. 



Vol.XVII.—Jvne, 1S07- F Exam* 



