94 PREPARATION OF ENGLISH CALOMEL. 
for removing the product of each operation. Lastly, the 
cylinder is set in a furnace in such a manner that the flame 
entirely envelopes it. 
The calomel is introduced into the cylinder, and a small 
quantity of corrosive sublimate is added, to supply chlorine 
to a portion of mercury, which appears to result from the 
partial reduction of the protochloride. But it is found that 
this decomposition may be almost entirely prevented, if, 
instead of using calomel, the substances from which it is 
produced be employed, mixed in the proper proportions. 
The calomel thus obtained is so pure, that it merely requires 
to be once washed. 
I could not believe for some time that an iron cylinder 
could be used, for it appeared to me that this metal would 
cause a decomposition of the protochloride of mercury, the 
iron being converted into perchloride with the chlorine of 
a part of the calomel, and this would be volatilized with 
the remaining calomel and the mercury, thus injuring the 
beauty and purity of the product; but on further reflection 
it appears that this change could hardly take place at a tem- 
perature so high as that which is necessary for working an 
apparatus containing many pounds of the materials for pro- 
ducing calomel. — Ibid. 
