possessing the Properties of Tannin. 325 



of the retort : as nothing more seemed to be produced, I 

 then jalscd the fire, when suddenly the vessels were filled 

 with a white cloud, and so great a portion of gas was al- 

 most explosively produced, as to overset the jar: this ^as, 

 by its odour, appeared to be ammonia, which in the first 

 instance had formed the white cloud, by combining with 

 the vapour of the nitric acid, with which the vessels were 

 previously filled *. Another jar was speedily placed in the 

 room of that which had been overturned, and a quantity of 

 gas was slowly collected : this proved to be carbonic acid, 

 excepting a very small part, w'hich was not taken up by so- 

 lution of caustic potash, and which, as far as the smallness 

 of the quantity would permit to be determined, appeared 

 to be nitrogen gas. There remained in the retort a very 

 bulky coal, which weighed eight grains and a half: this, by 

 incineration, yielded one grain and a half of brownish white 

 ashes, which consisted principally of lime ; but whether 

 any alkali was also present I cannot positively assert, as 

 the trace which 1 thought I discovered of it was very slight, 



I shall for the present postpone any remarks upon this 

 experiment, as I wish to proceed in the account of others 

 which have been made on the artificial tanning substance. 



G. Fifty grains of this substance were dissolved in four 

 ounces of water, and were afterwards precipitated by dis- 

 solved isinglass, eighty-one grains of which became thus 

 combined with forty- six grains of the tanning substance. 



The remaining portion of the latter was not precipitated, 

 and was therefore separated by a filter, and evaporated to 

 dryness. It then appeared in the state of a light brittle 

 substance of a pale cinnamon brown colour; and it is verv 

 singular, that although cliarcoal is an inodorous body, and 

 although the artificial tannijig substance, when properly 

 prepared, is likewise devoid of smell, (unless a certain pun- 

 gent sensation which may be perceived upon first opening 

 a bottle containing the powder after agitation should be so 

 termed, but which seems rather to be a mechanical effect,) 

 yet this substance possessed a strong odour not very unlike 

 prepared oak bark; and this odour became much more per- 

 ceptible when the substance was put into water ; iu which 

 it immediately dissolved. Tlie solution was extremely bit- 

 ter, and acted but slightly on dissolved isinglass, with 

 which, however, it formed some floccali ; with sulphate of 

 iron it produced a brown precipitate ; with nuiriate of tin, 



• After the experiment ihc receiver was fuuoJ to be tliiiily co;it>?d with a 

 white saline cruit. 



X 3 OIV 



