6 FORMATION OF SHELLS OF ANIMALS, ETC., 
free by the alkali, must have 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 arabic in common water, 
of 1:0844 specific gravity, one ounce of which will weigh 
520 grains. This solution 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 float- 
ing vegetable matter. It must also be added carefully 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 having 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 sub-carbonate of potash are contained in the gum, 
in combination with malic acid, and also in the common 
water ; ammoniaco-magnesian, or triple phosphate, is also 
contained in the gum, and is set free by the alkali. 
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 muriate were not 
in too great excess for the gum, in which case crystals of 
carbonate would be formed together with the globules, 
and the surface of the slide would become covered with 
coalescing patches of the latter. Also muriate of barytes, 
and muriate of strontia, when treated in the same manner 
as the muriate of lime, furnish each a globular carbonate, 
