M. Quevenne on Potygalic Acid. 561 



colour. The filtered solution contains chloride of lead, and gives with 

 nitrate of silver a copious precipitate of chloride of silver. 



It dissolves perfectly in nitric acid with the disengagement of ni- 

 trous acid, and the separation of a little sulphur. Nitrate of silver 

 added to this solution also gives a precipitate of chloride of silver. 



If it be heated by the blow-pipe on charcoal, it fuses, and disen- 

 gages sulphurous acid. Part of the lead is quickly reduced, whilst the 

 chloride of lead is volatilized in a white smoke. 



When the precipitate, separated from the chloride of lead by ebul- 

 lition, is heated in a glass tube, it becomes black, disengages sulphur 

 and sulphuretted hydrogen, and then fuses into a brown mass, which 

 crystallizes on cooling. 



Yellow precipitate. — This behaves in the same way as the red j ex- 

 cept that when the chloride of lead is dissolved by boiling in water, it 

 is converted into black sulphuret of lead, which when heated in a 

 glass tube does not disengage either sulphur or sulphuretted hydro- 

 gen. 



These results explain the difference which exists between these two 

 precipitates. As by the action of the chlorine or of the aqua regia 

 upon the sulphuretted hydrogen, hydrochloric acid is produced and sul- 

 phur set free, the latter combines with the sulphuret of lead, formed 

 at the same time, to produce sulphuretted sulphuret of lead, analo- 

 gous to that obtained by adding quintosulphuret of potassium to a so- 

 lution of lead, and this body combining with the chloride of lead, 

 gives the double compound of kermes colour, while the yellow preci- 

 pitate is merely a compound of sulphuret and chloride of lead, which 

 is decomposed by boiling in water. 



According to the experiments of M. Reimsch, copper and bismuth 

 appear to form similar combinations. A solution or copper, acidified 

 with hydrochloric acid, gave with sulphuretted hydrogen a deep green 

 blue precipitate, which when washed with water till free from uncom- 

 bined muriatic acid, and dissolved in nitric acid, gave chloride of sil- 

 ver on adding the nitrate. The same effect takes place with precipi- 

 tated bismuth ; except that it cannot be obtained pure, on account of 

 the difficulty of washing it. 



Zinc, which is generally admitted not to be precipitable from its 

 acid solutions by sulphuretted hydrogen, is however thrown down by 

 it from a solution of the chloride rather strongly acidified by hydro- 

 chloric acid. The precipitate obtained is a compound of sulphuret 

 and chloride of zinc. It dissolves in dilute sulphuric acid with a strong 

 disengagement of sulphuretted hydrogen ; but when subjected to ebul- 

 lition, the solution yields an abundant precipitate of chloride of silver 

 with the nitrate. — Journal de Pharmacie, Mai, 1837. 



POLYGALIC ACID. 



M. Quevenne prepares this substance by digesting powdered poly- 

 gala in alcohol of specific gravity 0*85 till it is exhausted. The greater 

 part of the spirit is to be distilled, and the syrupy residue is to be 

 treated with aether to remove the fatty matters. On standing, a pre- 

 cipitate is formed in the liquid ; this is 1o be separated bv the filter 



Third Series. Vol. 1 1. No 70. Dec. 1837. 4 C 



