42 
Rainey^ on Artificial Calculi. 
precise densities of tlie two solutions specified. As several 
applications have been made to me_, implying the want of 
explicitness in the first formula, I hope the tedious minute- 
ness with which the details of the present process are given, 
will be excused. 
This process consists in introducing into a two-ounce 
phial, about three inches in height, vv^ith a mouth about one 
inch and a quarter in width, either one ounce or half an 
ounce, by measure, of a solution of gum arable saturated with 
carbonate of potass (the sub-carbonate of the old Pharmaco- 
poeas) of 1'4068 specific gravity, when ,^ne ounce of this 
compound solution will weigh 672 grams. The solution 
must be perfectly clear, all the carbonate of lime which had 
been formed by the decomposition of the malate of lime 
contained in the gum having been allowed completely to 
subside. Next, two clean microscopic slides of glass of the 
ordinary dimensions, are to be introduced, with the upper 
end of one slide resting against that of the other, and with 
their lower ends separated as far as the width of the phial 
will permit ; and, lastly, the bottle is to be filled up with a 
solution of gum arable in common water of 1*0844 specific 
gravity, one ounce of which will weigh 520 grains. This solu- 
tion must also be perfectly clear, having been first strained 
through cloth, and then left to stand for some days to allow 
of the subsidence of all the floating vegetable matter. It 
must also be added gradually to the alkaline solution, that 
the two solutions may be mixed as little as possible in this 
part of the process. The bottle must now be kept perfectly 
still, covered with a piece of paper to prevent the admission 
of dust, for three weeks or a month. Time would be saved 
by employing a dozen bottles thus charged, and examining 
their contents at stated intervals according to the chief 
object sought for in the experiment. The soluble salts of 
lime to be decomposed by the subcarbonate of potass are 
contained in the gum, in combination with malic acid, and 
also in the common water. Muriate of lime dissolved in a 
solution of gum from which all the lime had been previously 
separated would answer a similar purpose, provided the 
quantity of muriate were not in too great excess for the 
gum, when crystals of carbonate would be formed with the 
globules, and the surface of the slide would become covered 
with coalescing patches of the latter. 
But there is another crystalline compound in gum, which, 
when I wrote my first paper, had not occurred to my notice, 
and which, combining with the globules of carbonate of lime 
formed at the lower part of the slide, contributes to the for- 
