10 
DR. HOSKINS ON THE DECOMPOSITION OF CALCULI, 
ting that the precipitate in the present instance was chiefly phosphate of lead*; it 
may likewise be fairly inferred, that the other ingredients composing the calculus 
had formed soluble salts with the malic and acetic acids of the decomponent. For 
it was manifest that the acids contained in cidre-aigre had formed soluble salts with 
oxide of lead, and that these salts, even when dissolved in such a quantity of fluid 
as to possess scarcely any taste and no pungency, were capable of decomposing 
phosphatic calculi. The liquid in this state, however, was objectionable, in a prac- 
tical as well as a scientific point of view, on account of its colour, odour, and 
indeterminate strength. It therefore became desirable to attempt the formation of 
some definite salt, of analogous composition, which, by solution in water, should form 
a decomposing agent, of a strength which might at all times be depended on ; capa- 
ble also of being varied according to circumstances. 
In theory, the nearest approach to an agent of this kind seemed to be a super malate 
of lead ; for, although the neutral malate was known to be insoluble in water, it was 
deemed possible that, by some modification, its solubility might be increased. This 
1 found to be the case. 
Crystals of malate of lead, in fine powder, were diffused in water, and thoroughly 
decomposed by sulphuretted hydrogen, so as to leave malic acid in solution ; this 
was filtered and boiled to expel the gas. While still hot, fresh crystals of malate of lead 
were added to the fluid, which was then allowed to cool, and again filtered. On sus- 
pending specimens of phosphatic calculi in this liquid (which, though sensibly acid when 
tested, was perfectly insipid), chemical action took place, but by no means rapidly. 
This w T as, nevertheless, one step towards the acquirement of a definite compound. 
Recurring to my former conjectures as to the nature of the salts held in solution 
by the filtered aigre, pure crystals of malate of lead were gradually added to warm 
dilute acetic acid'f-. This mixture was heated gently for some time, and afforded a 
better decomponent than the former, but still not so active as the original cider- 
vinegar compound. 
After a long series of experiments to the same effect, which it is unnecessary to 
detail, I arrived at the following conclusions : — 1st, that malic acid, unless concen- 
trated, exerts but little solvent action on phosphatic calculi ; 2nd, that a weak solu- 
tion of super-malate of lead does act as a decomponent ; 3rd, that a solution of aceto- 
malate, if I may be allowed so to call the liquid last described, is tolerably active ; 
but finally, that none of the preparations of malic acid, already alluded to, are so 
active as the cider-vinegar solution. 
The close resemblance said to exist between genuine malic acid, procured from 
the Sorbus aucuparia, and the factitious, prepared by the action of dilute nitric acid 
on sugar, induced me to turn my attention to what, by some chemists, is called sac- 
charic, by others oxal-hydric acid. By slightly varying Berzelius’s process^, so as 
to avoid the discoloration produced, as he says, by humic acid, a very pure saccharate 
* See p. 280. t Five parts of pure acid to 480 of distilled water. 
* This modification consists in heating the mixture of dilute acid and sugar, until the evolution of red fumes 
