136 Experiments upon the 



duces ill it a deep green colour, and soon afterwards a prc" 

 cipitate of the jame shade. 



6. Emetic, or antimoniatcd tartrite of potash, forms n a 

 precipitate in it. This substance, therefore, is not the same 

 as that which precipitates this njetallic salt, in the infusions' 

 of certain kinds of cinchona. 



7. Lastly, it reddens very sensibly turnsole tincture. 



The acidity of this substance, and the precipitation pro- 

 duced by the alkalis in its concentrated solution, made me 

 suppose that it was indebted for a part of its solubility to 

 the presence of the free acid which accompanies it : this 

 Seems to me to be founded upon its having been once sepa- 

 rated bv an alkali, washed and dried, and therefore not 

 longer soluble in water, except in a very small proportion. 



In order to acquire a greater degree of certainty upon this 

 substance, I put some of it into water acidulated by different 

 acids, and J saw that in fact it dissolved with facility, and 

 that its solutions resumed a bitter taste, similar to that which 

 it had before having been precipitated by the alkalis. 



I remarked that this substance retained, on being preci- 

 pitated, a portion of the alkalis employed for this purpose ; 

 at least, the following experiment seems to prove it. After 

 havinsr precipitated it from its aqueous solution by ammonia, 

 and washed it in a great quantity of water, I mixed with it 

 some caustic potash, which immediately developed an ex- 

 tremely sensible ammoniacal smell, which it did not pro- 

 duce before having been precipitated by this alkali. 



It is therefore evident that this substance is combined with 

 a portion of ammonia, which serves to precipitate it from 

 its solution ; at least, that the acid which accompanies it 

 naturally, only forms with this alkali an insoluble salt, and 

 mixes with the resinous matter 5 which seems very little pro- 

 bable. 



It woidd seem, according to these properties, that this 

 substance sometimes performs the part of an acid and some- 

 times that of an alkali, since it unites with those two kinds 

 of substances by neutralizing a part of their properties. 



If; after having precipitated this matter by the alkalis, 



we 



