Rainey, on Artificial Calculi. 45 
lime and gum act in the same way upon the triple phosphate 
as the simple gum did upon the pure carbonate of lime. 
Now a very simple fact will show that this reasoning is cor- 
rect, and that the repulsive force acting upon the molecules 
of the triple phosphate, as also upon those of the pure car- 
bonate in these compound globular calculi, is not destroyed, 
but only overbalanced by the cohesive attraction of the gum, 
and is there ready to display its repulsive power upon their 
molecules as soon as this balance is destroyed and a prepon- 
derance given to the repulsive agent. The fact here alluded to 
is shown by the immersing for an instant of a slide, on which 
calculi of triple phosphate combined with globular carbonate, 
and calculi of globular carbonate without triple phosphate 
have been formed, in any liquid heated to 212°, as, for in- 
stance, distilled water, turpentine, olive oil, Canada balsam, 
&c., when the molecules of the former of these calculi will 
instantly start from the curvilinear to the rectilinear arrange- 
ment, that is to say, will pass into well-defined crystals of 
various sizes, and of a more or less rhomboidal figure, whilst 
those of the latter calculi — the globular carbonate — will not 
be in the least affected. The explanation of this fact appears 
sufiiciently obvious. In the calculi containing the triple 
phosphate combined with the globular carbonate there is a 
smaller proportion of gum than in the globular carbonate 
calculus, and hence the excess of the attractive over the re- 
pulsive force may be presumed to be less in the former than 
in the latter calculi ; so that if the forces of attraction be 
equally weakened in both kinds of calculi at the same instant, 
one may pass into the crystalline state, whilst the other re- 
tains its globular form, as shown in the experiment. Now it 
is only necessary to suppose that heat, in this instance, has 
weakened these attractive forces."^ 
It seems to me that this experiment, in conjunction with 
the facts connected with the conversion of the crystalline 
into the globular form of carbonate of lime and ammoniaco- 
magnesian phosphate, by the action of a substance possessing 
a particular kind of cohesive attraction (for I may observe 
that gum is not the only substance which produces this 
eflPect), furnishes both analytical and synthetical evidence in 
proof of the correctness of the principle advanced in this and 
in my first paper. (See ^ Medico-Chirurgical Review,^ for 
July, 1857.) 
After the slides have been withdrawn from the bottles, all 
* It was mj intention to have made some observations upon the probable 
nature of the repulsive force and its action in the production of crystals ; 
but as such observations could only have been of a speculative cliaracter, I 
have thought it best to omit them. 
