260 Mr. Donovan on the [Oct. 



and that this is the red, is proved also by synthetical experi- 

 ments, the red oxide forming these salts by simple solution in 

 dilute nitric acid, no gas being discharged, and the oxide being 

 separated unaltered by alkalies. 



34. That the solution of mercury in nitrous acid (22) contains 

 nothing but nitrate and oxynitrate has been already proved : to do 

 so more satisfactorily, I added muriate of soda to such a solu- 

 tion. The calomel being separated by filtration, the clear liquor 

 was precipitated by pure potash ; the powder after edulcoration 

 and dessiccation was heated to redness in a green glass tube, as 

 already described (14), and the result with the proper allowance 

 for moisture convinced me that it was the peroxide containing 

 7*25 per cent, of oxygen. 



35. When the nitrate of mercury is heated, it is partly decom- 

 posed, the oxygen of the acid uniting to the oxide. If the heat 

 be sufficient, the mass passes into a beautiful red crystalline 

 powder, commonly called " red precipitate of mercury." Whe- 

 ther this substance be a subnitrate, or an oxide, has been much 

 disputed. Lemery says, " if spirit of salammoniac be sprinkled 

 on red precipitate, a grey powder is obtained." Neumann 

 affirms that if spirit of wine be distilled from red precipitate, a 

 spiritus nitri dulcis is obtained. And Boerhaave says, that red 

 precipitate, by the action of oil of tartar, is changed to another 

 powder. These changes only happen, v/hen the nitrate of 

 mercury has been but half calcined ; and from these imperfect 

 observations originated the present opinion. 



36. Indeed the experiment of Dr. Murray, of Edinburgh, 

 proves, that red precipitate is sometimes still so badly prepared 

 as to contain nitrous acid. He found that by boiling it in water, 

 and adding ammonia, there was a precipitate. I find also that 

 if pure red oxide of mercury be boiled in water, and if very little 

 dilute ammonia be added, a white cloud is produced ; for boiling 

 water dissolves a little oxide of mercury. For success, the 

 ammonia must be very dilute, and small in quantity. 



37. To ascertain the point in question, whether this powder 

 be a subsalt or an oxide, I levigated 120 gr. of red precipitate, 

 diffused it in an ounce of distilled water, and through this passed 

 an incessant current of washed sulphuretted hydrogen during 48 

 hours. The sulphuret of mercury being filtered off, the clear 

 liquor was distilled in a small retort until but one or two drops 

 remained in the belly. Here, had there been any acid, it would be 

 found concentrated, but it did not affect litmus, nor was litmus 

 paper hung in the vapour, while the distillation went forward, 

 affected. I repeated the very same experiment, except that one 

 grain of nitric acid was previously boiled with the red precipi- 

 tate and water. At the end of the distillation, the remaining 

 five or six drops instantly reddened litmus. This seemed to 

 prove that well prepared red precipitate contains no nitrous acid, 

 and is a true oxide of mercury. 



