18 ACTION OP LEAD IN DISTILLED AND RIVER WATER. 
nic acid, on the length of time it had been exposed in the 
solution. 
" As to the existence of either of the salts of lead men- 
tioned in a soluble state, I must confess that I differ with 
the two authorities I have named, and believe that what 
they consider to have dissolved is merely the hydrated 
oxide of lead held in a state of mechanical suspension, and 
for the following reasons found that, in repeating an 
experiment of Colonel Yorke 's, that of precipitating hy- 
drated oxide of lead and washing it with warm distilled 
water, that the filtered liquor gave a brown precipitate with 
hydrosulphuric acid, after all the soluble salts formed had 
been washed away ; but that on refiltering a portion of it 
through more than one filter, not the slightest discoloration 
was given to the liquor by the test ; and as Colonel Yorke 
considered that the soluble salt was the hydrated oxide, a 
greater quantity of which would exist, as already shown, 
at the commencement of the action of the lead on the wa- 
ter, I placed a piece of lead in distilled water, and carefully 
tested the filtered liquor daily, for some weeks, with hydro- 
sulphuric acid, but in no case could I find the slightest dis- 
coloration given to it. Now as the test is so delicate as to 
be capable of discovering, according to PfafT, a 100,000th 
part of the metal in solution, if, as Colonel Yorke states, a 
10,000th part of the oxide is held in solution, the test would 
of course have distinctly shown it. 
" Dr. Christison considering that the action of the forma- 
tion of a soluble salt of lead was due to the carbonate of 
lead becoming converted into bicarbonate by long expo- 
sure, I tested the liquid from one of the experiments I have 
before mentioned, when the lead in distilled water had 
been exposed to the action of the atmosphere for six years, 
and could not detect the slightest discoloration after the so- 
lution had been carefully filtered. I therefore conclude 
from these experiments, and I believe Dr. Thomson has 
previously arrived at the same result, that no soluble salt of 
