6't: Experimenls on a Sichstance, which possesses 



what I have stated in this letter will probably- be just as^ 

 ** erroneous" in Mr. Keith's views, that is, just as con- 

 formable to the opinion of all mathematicians viho are com- 

 petent judges, as mv various statements in the critique in- 

 serted in your Magazine for November. 



T am, sir, ycurs, &c. 

 The Reviewer of Bounij castle's Trigonometry, 



February 12th, 1S07. 



Xr. A third Series of Experiments on an artificial Suhstance, 

 which possesses the principal characteristic Properties 

 of' Tannin ; with some Remarks on Coal. By Charles ■ 

 Ilatchett, £5^. F. R. S.* 



§ I. 



In my former papers upon this subject, some account has 

 been given of the eflfects produced by sulphuric acid upon 

 turpentine, resin, and camphor; and I shall now state the 

 results of other experimenls made with the same acid upon, 

 a great number of the resins, balsams, gum resins, and gums, 

 the greater part of which afforded that modification of the 

 artificial tanning substance, which, for the sake of distinc- 

 tion, I have in the preceding papers denominated the third 

 variety. 



The process was simple digestion in sulphuric acid, after 

 which, the residuum was well edulcorated, and was then 

 digested in alcohol. This was separated by distillation, the 

 dry substance which remained was infused in cold distilled 

 water, and the portion dissolved was examined by solution 

 of isinglass, muriate of tin, acetite of lead, and sulphate 

 of iron. 



jNIuch sulph.ireous acid, carbonic acid, several of the 

 vegetable acids, particularly benzoic acid, (when the bal- 

 sams were employed,) and apparently water, were produced 

 during the operation ; but in this paper I shall only notice 

 two of the products, namely, the tanning substance and 

 the coal. 



* From the Transacliuns of the Royal Societij for ISOC. 



The 



