14 
DR. HOSKINS ON THE DECOMPOSITION OF CALCULI, 
currents produced in liquids by heat, continued until decomposition from saturation 
of the solution, or other causes had ceased. 
The same fragment was afterwards immersed in other solutions of a similar kind, 
with a view of ascertaining its rate of decomposition : — but after decomposition had 
been going on steadily for some time, precipitation suddenly ceased. Under the idea 
that precipitation had ceased in consequence of the solution having become saturated, 
fresh quantities were tried, but without any renewal of chemical action ; although 
other phosphatic fragments plunged into the same fluid were readily acted on. The 
cause of cessation, therefore, could only be attributed to some change in the character 
of the assay ; on examination, instead of being white, friable, and homogeneous in 
texture, it had become fawn-coloured, dense, and striated ; and yielded unequivo- 
cally, uric acid reaction. This accounted for the abrupt cessation of chemical 
action, and bore testimony to the effects of the saturnine solution on the phosphatic 
ingredients ; for it was evident that the latter had constituted the outer coating of an 
uric acid nucleus in the fragment under examination. 
The result of experiments with other salts of lead, as well as with those of mercury, 
baryta, and others, confirm the facts already stated; viz. that almost all supersalts 
of lead, especially with vegetable acids, act as ready decomponents of the calculi under 
consideration. Even the acetate, which in its neutral state is inert, becomes active by 
the superaddition of a minute quantity of its own proper acid: and, in like manner, 
the addition of a few drops of lactic*, malic, racemic, or formic acids to solutions of 
their neutral salts, produces a class of active decomposing agents, so effectual, that 
either of them maybe considered to afford secure means for discriminating the phos- 
phatic from other varieties of calculi. 
An interesting and perchance important circumstance connected with this part of 
the subject, relates to the strength of the solution, which appears to be in inverse 
ratio to its decomposing power. Thus, a saturated solution of acetate of lead, 
acidulated pretty strongly with acetic acid, is inactive; whereas, one grain of the salt, 
with five drops of the acid, dissolved in one fluid ounce of tepid water, produces 
rapid and steady decomposition. 
This fact has been carefully verified by repeated experiments ; for instance, the 
moment a portion of calculus, which had been steadily decomposing in a weak solu- 
tion, is plunged into a stronger, action abruptly ceases ; it is as suddenly re-esta- 
blished when the assay is returned to the weaker solution. This alternation from 
weak to strong, and the reverse, was often repeated with solutions variously modified, 
but invariably with the same general result. 
On first remarking the above circumstance, I was not aware that Berzelius had 
previously recorded a somewhat similar fact in relation to the action of weak solu- 
* When a fragment of phosphatic calculus is placed in a solution of super-lactate of lead, under the mi- 
croscope a dense areola at first surrounds it ; from this, after a time, radii proceed, until the assay assumes a 
stellar appearance, of dazzling whiteness. 
