1888.] Dr Woodhead on Mercuric Salts as Antiseptics. 243 
gramme of the salt with a slight excess of iodide of potassium in 1000 
c.c. of distilled water. We have thus formed a 1 to 1000 solution, 
not of hiniodide of mercury, but of a solution of the double iodide of 
potassium and mercury, just as above we have a double chloride of 
ammonium and mercury (?). 
It is this property of forming double salts with the more basic or 
positive metallic iodides, as those of the alkali metals and alkaline 
earths, that renders the biniodide available in a soluble form. A 
hot solution of the salt with iodide of potassium deposits crystals 
of potassio-mercuric iodide — 2(KIjHgl2)3H20 (Fownes). These 
crystals are decomposed by water, and there is then a separation of 
about half the mercuric iodide, the solution containing the salt 
2KI.Hgl2, which remains as a saline mass on evaporation. 
This combination of iodine, mercury, and potassium, used as 
above stated, instead of the bichloride of mercury, with the same 
series of reagents, gives the following results : — 
On adding 5 c.c. of blood to 50 c.c. of the antiseptic fluid there is 
not the slightest degree of opacity in the fluid. It remains beautifully 
clear and unaltered, even as to colour. At the end of ten days there 
is still no change, and the hmmoglobin bands are well marked in the 
spectrum. When stannous chloride is added to the filtrate a dense 
yellow precipitate is formed, which on being heated turns black, 
and there is as bulky a precipitate as if an equal quantity of the I to 
1000 solution of pure biniodide of mercury solution had been used. 
It is evident, therefore, that in this case the whole of the mercuric 
salt remains in solution. This is a most important point, as it is at 
once seen that mercury in the form of an iodide of potassium and 
mercury does not combine with an albumen, but remaining in 
solution it (unlike the corrosive sublimate, which combines with 
the albumen of the blood under these conditions, and loses its 
antiseptic power) retains its germicidal properties. 
As we have seen, choride of sodium acts with the bichloride of 
mercury as does the iodide of potassium with biniodide of mercury. 
The only difference therefore is really that of the different solubility 
of the salts in the pure form. The mercury combines more readily 
with either iodine or chlorine than with albumen, and if these be 
kept in excess no albuminate of mercury can be formed. 
If 1 c.c. of a saturated solution of common salt be added to the 
