162 Substance possessing the Properties of Tanmn. 



principal object, I have not thought it necessary to enter ab 

 present into too minute a detail of other particulars, and have 

 therefore only thus cursorily noticed some of the principal 

 ffFects produced by nitric acid on the resins, balsams, 8cc. 

 Those, however, who are conversant with chemistry, will 

 undoubtedly perceive that these eflects deserve to be accu- 

 rately investigated ; and that the resins, balsams, gum resins, 

 and gums, should be regularly examined by every possible 

 method, not merely on account of the individual substances 

 which mav become the subjects of experinient, but because 

 there is reason to expect that from such an investigationy 

 medicine, with the arts and manufactures, may derive many 

 advantages, whilst the mysterious processes and eftects of 

 vegetation may very probably receive considerable elucida- 

 tion. 



Concerning the third variety of the tanning substance, 

 which is produced by the action of sulphuric acid on the 

 resins, gum resins, &c., I shall here add but little to that 

 which I have already stated in the latter part of the second 

 section of my first paper, and in the account which I have 

 lately given of an experiment on camphor. 



This variety appears to be uniformly produced during a 

 certain period of the process, but by a long continuance of 

 the digestion I have reason to beheve that it is destroyed. 



Substances, such as the gums, which afford much oxalic 

 acid by treatment with other acids, do not apparently yield 

 any of this tanning substance. 



The enerey of its action on gelatine and skin is certainly 

 inferior to that of the first variety, into which however, as 

 we have seen, it may easily be converted by nitric acid. 



From the mode of its formation there does riot appear to 

 be any positive evidence that it contains nitrogen like the 

 first and second varieties, and perhaps the absence of nitro- 

 gen may be the cause of its less powerful action ; this I have 

 not as yet ascertained, but it is ipy intention more particu- 

 larly to notice in a future paper the general properties of this 

 substance. 



XXVI. u4 



