1815.] Elements of Organic Nature are comUned. 183 



ammonia till I restored the property of reddening litmus paper, 

 that there might be no excess of ammonia. The tannate of 

 ammonia thus formed mixed with a solution of muriate of barytes 

 lets fail abundance of tannate of barytes. I separated it by a filter, 

 and washed it with care. From the experiments of Sir H, Davy, 

 we know that the gallaie of barytes is soluble in water ; so that in 

 this experiment it is only the tannate which is precipitated. The 

 tannate of barytes mixed with diluted sulphuric acid furnished a 

 super-tannate of barytes soluble in hot water. 'J'o this solution I 

 added diluted sulphuric acid till almost the whole was decomposed. 

 1 filtered tiie liquid thus obtained, which had a very astringent taste, 

 and strongly reddened litmus paper. This last property was not 

 owing to tlie presence of sulphuric acid, for the liquid still retained 

 tannate of barytes in solution. I now mixed it with caustic 

 ammonia till the tannate of barytes began to precipitate. This 

 solution of tannate of ammonia, with a small excess of tannin, was 

 mixed with neutral nitrate of lead as long as any precipitate fell. 

 The tannate of lead thus obtained had a yellowish colour, and 

 became somewhat brown while washed. On examining the com- 

 bination of tannin with oxide of lead, I found that the oxide has a 

 strong propensity to combine with an excess of tannin, and that the 

 precipitate obtained was in reality a mixture of tannate and super- 

 tannate of lead. I found that the super-tannate might be rendered 

 neuter by boiling it in water as long as that liquid separates tannin. 

 The water dissolves no part of the oxide ; and the tannate which 

 remains undissolved is neutral. If the precipitation of the tannate 

 takes place at 212" there is very little super-tannate formed. 



Neutral tannate thus prepared was dried in a vacuum, not to be 

 exposed to the influence of the oxygen of the air, by which it is a 

 little altered. 



Tannate of lead obtained at different times, though by the same 

 means, was analyzed by combustion. It gave 34-12, 34'21, 34-5(> 

 per cent, of oxide of lead, probably as the excess of tannin was 

 more or less completely removed. Hence this tannate is com- 

 posed of 



Tannin GS-yj) 100 



Oxide of lead 34"J1 52 



100-00 



Now 52 oxide of lead contain 3-718 of oxygen. 



When I attempted to obtain a subtannate of lead by means of the 

 action of amnioiiia on the neutral tannate, 1 obtained a tannate of 

 a browner colour, and very raucous; but which, after being washed 

 and dried in a vacuum, gave 34 G per cent, of oxide of lead, 

 licnce it would appear that ammonia does not decompose the 

 neutral tannate ; just as happens when we add an excess of alkuli 

 to the tannate of the same alkali. 



There i'^, liowever, a subtannate which 1 obtained by precipitating 

 tannate of ammonia with a boiling solution of subuitratc of lead . 



