
WITH SOLUBLE LEAD SALTS. 309 
of carbonate of lime can be dissolved, independently of the continued presence of 
the free acid, to cause the appearances referred to. 
I next tried the solvent action of water alone on finely divided carbonate of 
lime. Distilled water, which had been boiled and cooled, was left in contact 
with marble in impalpable powder for several days in a close vessel. It was 
then found by the action both of acetate of lead and of oxalate of ammonia, that 
rather more carbonate of lime had been taken up by the pure water than was left 
in solution after boiling the carbonated water, but still that the amount was con- 
siderably less than the reactions which have been referred to, indicate in ordi- 
nary natural waters ; and it is remarkable that the effect of the lead salt is usually 
more decided than that of the oxalate. 
I incline, therefore, to think, that the carbonate of lime present, in such cir- 
cumstances as have been described, has a different origin, viz., Double Decompo- 
sition, between a lime-salt and a carbonated alkali; as it would seem that the 
carbonate of lime formed is, in this kind of nascent state, dissolved more readily 
than when precipitated by boiling from a carbonic solution. The following expe- 
riments illustrate this origin of the reaction. To half an ounce of distilled water, 
a few drops of a solution of sulphate of lime in water were added. A single drop 
of solution of chloride of calcium, and a single drop of solution of carbonate of 
potash were then added. The liquid remained quite transparent, and did not 
affect turmeric or cabbage paper. When boiled it still remained transparent. 
When a drop of solution of acetate of lead was added to a portion of this liquid, 
either before or after boiling, a considerable white cloud was formed, which dis- 
appeared on the addition of a drop of acetic acid. Thus was the reaction of the 
spring waters exactly imitated. I at first inclined to think that in such cases no 
actual double decomposition ensued until the liquid was concentrated by heat, 
and that the action on the lead-salt was due to the carbonated alkali present. 
But farther experiments lead me to believe that the carbonate of lime is actually 
formed, at least to a considerable extent, and then dissolved by the water ; for, 
if a couple of drops of solution of chloride of calcium and a drop of solution of 
carbonate of potash be added to a few drops of distilled water, muddiness will be 
produced; and this will disappear when half an ounce of distilled water is 
shaken with the mixture, without any deposit being formed by rest. The solution, 
however, of the carbonate of lime is dependent on the action of the water taking 
place either on the nascent salt, or at least immediately after its formation ; for I 
found that when carbonate of lime, precipitated by double decomposition, was col- 
lected on a filter, washed, and allowed to stand some minutes, and then left in con- 
tact all night with boiled and cooled distilled water, acetate of lead had only a 
very feeble effect on the liquid. 
It was, of course, necessary, in order to establish this view, to ascertain that 
those natural waters which exhibit the reaction referred to, actually contain 
