Rainey, on Artificial Calculi. 
47 
lime has to combine with hard substances. The slide upon 
which these particles have been formed is permanently 
marked by the part of the globule which had thus been 
attached to it. The particles on a slide^ where the experi- 
ment has perfectly succeeded^ come in the following order, 
taking them as they are seen from above downwards. First 
come the minute spherules and dumb-bells, which get larger 
as they are situated lower on the glass ; next, the particles 
are seen to get smaller, though of a more perfectly spherical 
form, and here begin to be mixed with very large globules. 
These, having the most carbonate in their composition, exhibit 
a laminated arrangement, whilst those which are chiefly com- 
posed of triple phosphate have their surface nodulated, 
being studded with minute crystals ; this is especially the 
case in the calculi which have been several months in the 
solution ; lastly come the crystals of triple phosphate passing 
into a globular form, being mixed only with a small propor- 
tion of globular carbonate ; and, last of all, are the crystals 
of pure triple phosphate, with their sides and angles beauti- 
fally sharp and t well formed. These appearances, and 
the proportions in which these several kinds of globules 
exist, will vary in different specimens, depending probably 
upon differences in the composition of the different kinds of 
the gum employed in the experiment, as well as upon other 
accidental causes."^ 
There is yet another description of artificial calculi pre- 
senting characters differing in many respects from those 
already described, prepared by dissolving one pound of gum 
arable in two pints of water, and straining the mucilage 
through a fine hair sieve, and then putting one pint of the 
solution with two ounces of subcarbonate of potass, well 
mixed together, into a quart bottle, and after twenty-four 
hours adding, by means of a syphon, the other pint of mu- 
cilage,t and after that leaving the bottle at rest for six 
weeks or two months, when the calculi will be found 
adherent to its sides, or in the fluid at the surface. 
* Besides these, there are other crystals formed in these solutions, but 
they are all soluble excepting those of bicarbonate of lime, which are pro- 
duced by some of the carbonate becoming combined with the carbonic 
acid set free by the action of the acetic acid upon the subcarbonate of 
potass. The quantity of the acid being the result of the acetous fermenta- 
tion, is most abundant in warm temperatures. All crystals produced 
by double decomposition in a solution of gum, which do not combine che- 
mically with it, are large and well-formed ; lience such a process may be 
taken advantage of to crystallize some salts, otherwise difficult of 
crystallization. 
f It may be observed that in this instance the insoluble particles floating 
in the mucilage will not have had time to fall to the bottom of the bottle. 
