Litelligence and Miscellaneous Articles. 387 



and I should content myself with the publicity which I have given to 

 them in my lectures, if M. Henry, jun., who has lately published an 

 interesting memoir on kermes, had not left me some observations to 

 add. I shall distinguish the precipitates formed by sulphuietted hy- 

 drogen in a solution of antimony from kermes, properly so called, be- 

 cause their natures are very different. 



The orange red precipitate, obtained by passing sulphuretted hy- 

 drogen into a solution of emetic tartar, is an hydrated protosulphuret 

 of antimony. In fact, neither weak muriatic acid nor tartar separates 

 any oxide from it ; and when solution is effected, it is always accom- 

 panied with the disengagement of sulphuretted hydrogen. 



This sulphuret when dried at 212° Fahr. contains some water, but 

 not in quantity sufficient to form an hydrosulphuret ; it is gradually 

 expelled up to 446° ; at this point it contains no more, and becomes 

 black ; when rubbed on paper it gives black marks. It appears to 

 me analogous to hydrated peroxide of iron, which loses its water gra- 

 dually, becoming more and more brown, as the temperature rises, and 

 assuming a red colour only when it has lost all its water. 



Sulphuretted hydrogen produces also a red precipitate in the solu- 

 tion of permuriate of antimony, but it differs from that obtained from 

 emetic tartar or the protomuriate ; it is an hydrated persulpluuet, 

 which heat decomposes into sulphur, which is volatilized and black 

 protosulphuret, similar to the preceding. It is to be observed, that 

 the black sulphuret obtained by calcining the orange-red sulphuret, 

 is less fusible than the native black sulphuret j it resists the action of 

 a spirit-lamp. 



It is well known that kermes varies in colour, at least, according 

 to the mode adopted in preparing it. It is that obtained by the pro- 

 cess of Cluzel (Antialen cle Cliimie, torn. Ixiii. p. 122), upon which my 

 observations will be made. Wis sliall be greatly deceived if we sup- 

 pose that because kermes stiil yields something to water, after nu- 

 merous washings, it is pure only when it ceases to do so ; for if we 

 were to vvash the subacetate of copper, and many other salts, till 

 water ceased to dissolve any portion of them, they would be com- 

 pletely decomposed. The fact is the same with kermes, too much 

 washing alters its nature. At what point then ought we to stop ? 

 This is readily discovered by employing the smallest possible quantity 

 of water in the washings, and in continuing them only until the resi- 

 due, su])|)osing the water to have no chemical action upon it, contains 

 only one-thousandth or a ten-thousandth of foreign matter. 



Kermes mineral, thus washed, has the following properties: — dilute 

 muriatic acid, tartaric acid and bitartrate of potash, take protoxide of 

 antimony from it without disengaging sulphuretted hydrogen ; when 

 dried for a long time at 7°, and even at 212°, it still contains water ; 

 heated by a spirit-lamp it becomes black, and yields water, which, as 

 observed by M. Uobiquet, is slightly ammoniacal. At a higher tem- 

 perature it fuses and swells up, on account of a little sulphurous gas 

 which is disengaged. When in layers upon glass, it gives it a deep 

 red colour, and rubbed upon paper it gives a reddish-brown colour : 

 it is more fusible tluin the black sulphuret obtained by the calcina- 

 3 D 2 tiou 



