possessing ike Properties of Tannin. 1 61 



pearcd partly to counteract the formation of the tanning sub- 

 stance; but oxalic acid, when formed in any considerable 

 quantity, seemed absolutely to prevent the formation of this 

 substance ; for whilst abundance of the former was obtained 

 froui gum arable, tragacanth, manna, and guaiacum, not 

 any of the latter could be produced. 



Common liquorice appears at first to be an exception; but 

 from the smallness of the quantity, and the colour of the 

 precipitate which it produced with solution of isinglass, I 

 am almost convinced that the tanning substance was formed 

 by the action of the nitric acid on a portion oF uncombined 

 carbon, which, being in a state approaching to coal, is pro- 

 bably the cause of the blackness of the common liquorice. 



As the formation of the tanning substance has been my 



such as the camel, the horse, and the. cow, {Systime dcs Cnvnoissavrfs Chi- 

 ir.h]iies, par Fourcroy, 4tO edit. torn. iv. p. 158;) yet all this certainly ap- 

 pears to be in favour of its being a chemical product. 



I have observed, when benzoin, balsam of Tolu, and balsam of Peru, were 

 dissolved in sulphuric acid, that a great quantity of beautifully crystallized 

 white benzoic acid was sublimed during digestion ; and as it is produced in 

 so very pure a state by this single and simple operation, I would recommend 

 a trial of the process to those who prepare benzoic acid for commerce ; but 

 I am not certain whether this mode may prove more oeconomical than those 

 v/hich at present are employed. 



Wlien dragon's blood, however, was treated in the same manner vnx\\ sul- 

 phuric acid, I could not obtain a particle of benzoic acid; nor did I succeed 

 much better when I had recourse to lime, according to Schcele's process; for, 

 although a considerable quantity of the substance v.as thus rendered soluble 

 in water, yet by the addition of muriatic acid I obtained only a slight appear- 

 ance of benzoic acid, accompanied by a copious precipitate of red resin, not- 

 withstanding that the solution had acquired a powerful and peculiar balsamic 

 odour. 



But In a former part of this paper I have stated, that when dragon's blood 

 was dissolved in nitric acid, and afterwards evaporated to dryness, it yielded 

 about 6 per cent, of benzoic acid. Now, if this had been originally present 

 in dragon's blood in the state of benzoic acid, some stronger evidence of it 

 might reasonably have been expected in each process ; but this not being th« 

 ca.e, I am inclined to consider it as produced, and not educed, by the action 

 cf the nitric acid on the original principles of the dragon's blood ; and I am also 

 persuaded that similar but more general efTects take place v/hen benzoin ©r 

 any of the balsams are subjected to the different processes by which benzoic 

 acid is obtained ; so that to me this last seems to be as much a chemical pro- 

 duct as the oxalic, the acetous, and other of the vegetable acids. 



The succinic acid also appears to be a product and not an original ingre- 

 liirnt of amber. 



Vol. 24. No. 94. March 1606. L principal 



