30 TANNING MATTER, &C. 



Experiments, for 1S04, p. 208, I have ' particularly endeavoured to 

 &c. on an am- , i % i , , 



ficial substance '^"^w, how powerfully the acetic acid acts upon resin, 



having thecha- gluten, and some other substances ; so that it may justly 

 ning matter. ' ^'^ rt»garded, as a valuable agent in the chemical analysis 

 of vegetable bodies. In this point of view, it is as a sol- 

 vent to be (he more highly appreciated, because it appears 

 to dissolve the resins, &:c. without affecting their respect- 

 ive qualities, and thus by proper precipitants, these sub- 

 stances may be separated from it pure ami unaltered. 



I am induced therefore to consider acetic acid to be the 

 true acid solvent of the resinous substances, as it dissolves 

 them speedily, without producing any apparent subse- 

 quent change in their natural properties. 



Siilphuric acid also, almost immediately dissolves th^ 

 resins, balsams, «fec. and forms transparent brown or 

 sometimes crimson solutions, the latter colour being most 

 commonly characteristic of the balsams. 



These solutions, however, are difierent fiom those made- 

 inthe acetic acid, by not being permanent, for from the 

 moment when the solution is completed, progressive al- 

 terations appear to be produced in the body which is 

 dissolved ; thus turpentine is almost immediate]}^ convert- 

 ed into resin, then into the third variety of the tuiinifu^ 

 t^ubstance, 'ind lastly into coal. 



Without being under the necessity of adducing other 

 examples, we may therefore state sulphuric acid to be a 

 solvent of the resinous substances, but which continues 

 afterwards to act on their principles, so as to decompose 

 them, coal being the ultimate product. 



Nitric acid, as I have shewn in the course of these Pa- 

 pers, and likewise on some former occasions, dissolves the 

 resins, but the progress of its effects seems to be converse- 

 ly that of sulphui-ic acid ; in the latter case, solution 

 precedes decomposition ; but when nitric acid is em- 

 ployed, decomposition to a certain degree precedes solu- 

 tion ; for it at first converts the resins into a pale orange 

 coloured brittle porous substance, then into a product, 

 which apparently possesses the intermediate characters of 

 vegetable extractive matter and of resin, and lastly, this 

 is converted into the first variety of the tanning substance, 

 beyond which 1 have not been able to effect any change. 



As 



