'Ccesalpinia coriariaf or Dividivi. ISK 



not effectually precipitate all the gallic acid from the catechu, 

 which therefore appears to contain a principle having a superior 

 affinity for the gallic acid. 



6. Subcarhonate of potash was the next test used. It preci- 

 pitated only sumach and galls, and with both likewise produced 

 a black cream, which, by the action of air, dissolved, and ren- 

 dered the upper part of the solution very dark ; column 10. 



7. Sulphuric acid, in a diluted state, was next tried, column 

 11, and this occasions precipitates in the infusion of kino and 

 pomegranate a little, which tended to subside in that of cate- 

 chu, no effect at all on the infusions of sumach and tormentilla 

 root, and almost none upon the rest. Whether the substances 

 precipitated by the acid be of an acid nature, and those precipi- 

 tated by the alkali alkaline, I leave for a future opportunity of 

 trying. 



8. One part of isinglass dissolved in 32 of water, was the 

 next substance which I experimented upon. Sir H. Davy con- 

 siders that it combines with the tanning principle in the pro- 

 portion of 54 to 46 of tannin. Half an ounce of each infusion 

 was added to half an ounce of the solution of isinglass, and the 

 results are given in columns 12 and 13. The leather precipi- 

 tated immediately like a resin, from the infusions of dividivi and 

 galls, but the sumach was rendered milky, and so continued for 

 more than a week without precipitating. The infusion of galls 

 continued also milky, but in a less degree than the sumach, not 

 precipitating at once so completely as the dividivi : at length 

 one-eighth of a grain was obtained from the sumach. It is pro- 

 bable that a stronger infusion of sumach would have afforded a 

 more copious and more precipitable substance : that from ca- 

 techu formed a tenaceous ring of leather at the bottom of the 

 phial, while all the rest were flocculent, and very different in 

 colour and appearance from these. The other precipitates, ex- 

 cept those from dividivi, galls, and sumach, melted in the gentle 

 heat to which they were exposed in drying, and, as they thus 

 became inseparable from the paper, they were not weighed. I, 

 however, wished to determine the weight of the precipitate from 

 oak.bark, and therefore repeated the experiment, drying the pre- 

 cipitate with more care, and then weighing it. Upon the elu- 

 triation of gelatine, tincture of muriate of iron produced an ef- 



