52 On some of the Combinations of Mercury. 



gether with these, deutochloricle of mercury (corrosive sub- 

 limate) and a portion of pronitrate of mercury with an excess 

 of oxide. To prove the accuracy of this result, I triturated 

 together chloride of sodium and protochloride of mercury, 

 adding a little water and applying a gentle heat, and found 

 the materials gradually became blue, a change attributable to 

 the decomposition of the protochloride, and proving the unfit- 

 ness of the chloride of sodium for the purpose intended. I 

 think it is probable that the change is owing to the formation 

 of a triple compound of deutochloriilc of mercury and sodium, 

 in which the proportion of chlorine to mercury is as two to 

 one, one proportion of which being abstracted from a portion 

 of protochloride leaves in it an excess of oxide, and hence re- 

 sults the blue colour. 



Finding these results, I employed muriatic acid instead of 

 the chloride of sodium, which threw down a precipitate of pure 

 calomel, and this preparation appears to me to act upon the 

 system more mildly than calomel obtained by sublimation. To 

 procure it, the following formula may be employed : 



Take of purified mercury seven ounces, nitric acid two 

 ounces and a half, water five ounces, pour the acid diluted 

 with the water upon the mercury in a glass vessel, and when 

 the effervescence has ceased, digest with a gentle heat, till the 

 effervescence again ceases. Raise the heat a3 the effervescence 

 ceases till it boils, and continue to boil for one hour, adding 

 boding- water from time to time as the fluid evaporates. Pour 

 off the solution from the residual mercury, and add ten pounds 

 ol boiling water. Lastly, add muriatic acid till it ceases to 

 throw down a precipitate. Wash this precipitate with warm 

 distilled water, so long as the fluid poured off changes the 

 colour of litmus, and then dry it. 



More mercury is here directed to be used than the acid can 

 dissolve, but, by using an excess, the whole of the acid is more 

 readily neutralized. By using no heat at first, and raisin- it 

 gradually, the formation of pei nitrate is prevented, but should 

 any portion of it be formed, it is in the course of the action 

 decomposed by the mercury and converted into pronitrate. 

 However, should any portion of it when formed, not be de- 

 composed as it forms with chlorine a soluble compound, it is 

 removed by the washing, thus leaving the calomel perfectly pure. 



To prepare the red oxide from the pronitrate, the following 

 process may be used : ° 



Dissolve the mercury in the acid and water as before di- 

 rected, using the same proportions. Having poured off the 

 solution from the mercury, add nitric acid half an ounce. 

 Evaporate till a white mass remains, which being rubbed to a 



