240 OBSERVATION* ON MURIATIC ACID; 



precaution abfolutely neceflary, in this n \»)de of operating, is; 



that while the mercurial fait is in an open veflel, it fhould not 



be expofed to a degree of heat capable of volatilizing any part 



of it. 



London Phar- The quantity of mercury ordered in the London Pharma- 



f 13 ^ 1 tta Pre "h C0 V (£ia -* to convert corrofive fublimate into calomel, is 9 pounds 



mercury in the of mercury for every 12 pounds of corrofive fublimate. But, 



formula for cor. f rom t } ie aDove experiments^ it would appear, that a fmalle'f 



is prudent. quantity of mercury might ftridtly anfwer. However, from 



the remits of minute invefligation, we mould not conclude 



too nattily upon preparations on the great fcale ; and> I rather 



think, that the excels of mercury ordered by the Pharmacopoeia 



is. a ufeful precaution. 



In attempts to In my experiments, I attempted to reduce, by means of 



reduce the mer- j r or z \ nc ^ ne me rcury contained in the mercurial 



cunal falts by * r * ' ' ' , . . 



other metals, falts. Iron did not anlwer the purpoie : zinc precipitated thd 

 iron failed, zinc merC ury a little better; and copper produced a change which 

 mercurv, and I did not expecl. If a bit of copper be put into a folution of 

 copper orecipi- corrofive fublimate, a white powder fhortly falls to the bottom; 

 from cor! tub. anc * tnat P ow der * s calomel. When waflied, it does not contain 



an atom of copper, or of corrofive fublimate. 

 Calomel is the Before I conclude thefe confi derations, I mult fay, that 



fame whether w l ie ther calomel be prepared in the dry or in the humid way *, 

 produced in the * * . 



humid or dry lC 



way: and alfo 



cor. fub. » By the humid way, I do not mean precifely the method of 



Observations on g h j That c j iemi ft de fi re s us to boil the acid with the mercury, 

 Scheele's humid ; '* 



procefs for calo- after they have ceafed to act upon each other at a low temperature, 

 mel. It is not gy this method, the nitric acid takes up an excefs of mercurial ox- 

 pure, but con- jj e an j t j ]£ n j trate f m ercury thus formed, precipitates by water, 

 tains a fub-ni- 7 ... c ,- , 11 



ttate of mercury. Therefore, when this nitrate of mercury is poured into the dilute 



folution of muriate of foda, according to the formula of Scheele, the 

 action, on the part of the folution, is twofold. 



]JL The water acts upon one part, and precipitates an oxide, or 

 rather an infoluble fub-nitrate of mercury. And, 



Idly. A double decompofition takes place between the nitrate of 

 mercury and the muriate of foda. It is with reafon, that the medi- 

 cal world have fuppofed the calomel of Scheele to be different from 

 that prepared in the humid way j for it is, in facT, calomel, plus an 

 infoluble fub-nitrate of mercury. In the flrft part of Scheele's pro- 

 cefs, there is difengagement of nitrous gas, together with oxidize- 

 ment and folution of feme of the mercury. When he boils the acid 

 upon the remaining mercury, there is no further difengagement of 



g»sj 



