PREPARATION OF PROTOIODIDE OF MERCURY. 251 
The iodine is triturated with the mercury, and small por- 
tions of alcohol of 36° or 40° added to moisten the mixture, 
which first assumes a reddish colour but soon becomes of a 
yellowish green. All the mercury and iodine disappear in a 
short time, and the combination is effected. 
The alcohol by its tendency to dissolve the iodine and the 
deutoiodide of mercury that forms, probably determines the 
combination of the two bodies. Too large a portion of the 
mixture should not be acted upon at a time, for there is so 
great an extrication of heat, that the whole mass will become 
fused, and a portion of the iodine will be volatilized, and of 
course, a compound of equal atoms will not be obtained. 
The protoiodide may also be prepared by triturating 100 
parts of deutoiodide of mercury with 44.50 of mercury and 
adding alcohol as above. In this operation the deuto is 
changed to a protoiodide. 
I therefore employed the mercury and iodine in the pro- 
portions of atom and atom, and not as is stated by M. Boutig- 
ny in those of two of mercury to one of iodine. Moreover, 
it will be presently seen that the quantities of iodine and mer- 
cury which exist in the salts employed by that chemist are 
exactly the same as those indicated by me. 
Besides, 1 cannot see how I could be accused of thus em- 
ploying two atoms of the metal to one of the iodine. As has 
been shown by the experiments of distinguished chemists, the 
protoxide of mercury is composed of 2 atoms mercury and 1 
atom oxygen, and one atom of oxygen corresponds to two 
atoms of iodine. The protoxide of mercury corresponds to 
the protoiodide. Consequently two atoms of mercury and 
two atoms of iodine must give the protoiodide or in other 
words a combination of mercury and iodine, atom for atom, 
and this is the combination I indicated. 
I will now show that the method of M. Boutigny, which I 
had already tried, is far from possessing the advantages and 
the degree of perfection he ascribes to it. 
His formula: 
Dry hydriodate of potassa £iv. 5 Hydriodate potassa 20 parts. 
Calomel 
