OJif ORPIMENT ATfD REALGAR. /,> 



Those of the second refer to the analysis of orpiraent and For the second 

 realgar in the humid way. As they obtained from the lat- 

 ter much more oxide of arsenic, and less sulphur, than from 

 the former, their conclusion appeared to them just. 



Those of the third argue from analogy. They imagine, For the tlurJ. 

 that, when a metallic solution is precipitated by a hidrosul- 

 phuret, the sulphuretted oxide that i$ formed is always of 

 the colour of the oxide it contained. 



It is easy to perceive, that none of these reasonings are All liable to 

 free from objection : and hence I have imagined it would not 

 be useless, to subject both orpiment and realgar to a fresh 

 examination, in order to tind with precision how they differ 

 from each other. 



But before I speak of the experiments however, which I promt says, 

 have made with them, I ought to quote what prof. Proust that » in P re * 



o • -i t i i i-ki i -%,-r t txr paring orpi- 



says or orpiment in the Journal de Physique, vol. XL1X, ment 



pp. 411, 412: particularly as I am perfectly of his opinion 



respecting the nature of this compound. 



" Things happen differently," says Mr. Proust, " when, 



instead of applying potash to the sulphuret of antimony, 



we add it to the ore of arsenic : the sulphuretted hidrogen, 



that is formed while the arsenic becomes oxided, does not 



adhere to this oxide, on precipitating it with an acid, as 



happens to that of antimony. The hidrogen acts a very the oxide of 



different part during this precipitation : it is employed i n a'-smcisdc- 

 ,. • ,. , ? ' . v , . , . comnosedbr 



disoxidmg the arsenic, in order that it may attach itself as the hidrogen, 



a metal to the sulphur, and produce the yellow sulphuret, and lhe arse " 



1-1 n • n i i • i • i „ nic unites in. 



which we call orpiment : tor the hidrosulphuret of arsenic, the metallic 



and the sulphuretted oxide, are two combinations that ap- stale with tna 



it xo ■,• ■ ! • . suluhur. 



patently do not exist. It we dissolve white arsenic in tho- 

 roughly saturated hidrosulphuret of potash, and afterward 

 add an acid, orpiment is precipitated without the least dis- 

 engagement of gas, without the slightest smell : but on the 

 one hand the sulphuretted hidrogen is no longer to be found, 

 and on the other the arsenic in the orpiment is in the metal- 

 lic state: in this precipitation therefore water is formed. The 

 pure regulus of arsenic is not soluble in the arsenical hidro- 

 sulphuret." 



If 1 might be permitted to make one observation on this Hi* experi- 

 passage in Mr. Proust's paper, I would say, that, it seems meuts scycely 



to 



