ON ARTIFICIAL TANNIN. 371 



portion which does not dissolve cedes a part of its acid to 

 that which dissolves; and, when the washings are afterward 

 evaporated, a farther division is made of the acid between 

 the substance A*, which is precipitated, and A 3 , which 

 remains in solution. 



Nitric acid, at least in the proportion in which I em- Attempt to 

 ployed it, could not convert A 1 into the tanning matter of convert &*»■& 

 Hatchett, which is very soluble in water. There is a por- 

 tion of matter, however not separated by water from the 

 nitric solution of A", which precipitates gelatine; but I 

 cannot assert, that it is absolutely similar to the matter of 

 Hatchett. 



To find whether it were possible, to remove the nitric The nitric acid 

 acid from A 1 without heating it, I digested it in a weak so- not separable 

 lution of neutral carbonate of potash. By the assistance bonate of pot* 

 of heat carbonic acid was evolved, and nearly the whole ash * 

 was dissolved. 



This solution was decomposed by sulphuric acid, which 

 threw down a brown flocculent precipitate. The superna- 

 tant liquid was colourless. It was filtered : the slight excess 

 of sulphuric 'acid contained in it was saturated with car- 

 bonate of potash: it was evaporated to dryness, and the 

 residuum was treated with alcohol at 30° [sp. gr. 0*868], 

 to dissolve the nitre, if it contained any; but none was 

 found. The carbonate of potash therefore had taken no 

 observable quantity of nitric acid from A'. 



The brown precipitate left on the filter was washed with After it is sepa- 

 hot water, till this gave no farther indication of sulphuric ra ^ ed from P ot " 

 acid to the test of solution of barytes. At this period the ric acid rather 

 water of elutriation was fawn-coloured, had a taste and more solublc » 

 smell slightly inclining to those of oak bark and roses, and 

 did not perceptibly precipitate gelatine. On adding an acid, 

 a little flocculent precipitate fell down. 



If water dissolve more of A* that has been precipitated 

 from potash by sulphuric acid, than of that which has not, 

 I believe it depends on its being more minutely divided;, for 

 in that which I prepared with care I found no sensible from being 

 quantity of sulphuric acid*, and its coal afforded only an ^•J.? 1 ' 1 ^^ 

 atom of potash. 



' * Experiments I have since made lead me to think, that potash 

 contributes to the solution of this substance in water. 



2 C 1 5 dec. 



