Dr: Pearfon’s Experiments on Caleuli. 271 
4. Bergman frequently mentions the red colour affumed 
by the nitric folution of the urinary calculus when fponta- 
neoufly evaporated in the air, or by the action of fire; even 
when it does not contain an excefs of free nitric acid: he 
obferves that this colour difappears by the addition of acids 
and alkalies; that it becomes black by the action of a {trong 
fire; that the calculus thus diffolved and evaporated is after- 
wards foluble in all acids; that by employing the nitric acid 
too much concentrated, the calculus is wholly reduced into 
froth ; that the fudden fwelling-up of the folution when ra- 
pidly heated is confiderable, and the foam of a bright red; 
that alkalies do not feparate the calculus from the nitric acid, 
ut unite with it as they de when two acids are prefented ta 
them; that the red mafs obtained by evaporation of the mi- 
tric folution is very different from the concrete acid of the 
calculus in its colour, its deliquefcence, the rofe-coloured 
tint which the fmalleft quantity of it communicates to water, 
its folubility, and its lofs of colour by the muriatic acid, the 
fpots which it leaves on the fkin, on bones, glafs, paner, 
efpecially by the aid of timeand heat. He aferibes thefe re+ 
markable effects to the alteration produced in the native acid 
_ of the urinary calculus by the nitric acid, rather than to 2 
precipitation with the latter. 
5. Bergman, in mentioning that he made many other ex- 
periments on the ftone of the bladder, takes care to point out 
that they prove nothing more or any way different from 
what Scheele has faid in his excellent memoir. All re- 
fearches, fays he at the end of his addition, for the purpofe 
of difcovering a remedy for this difeafe, ought to be founded 
on a perfeét knowledge of the properties of the calculus. He 
obferves that alkalies are the only truly active remedies, 
the efficacy of which has been acknowledged by medical 
experience, in concert with chemical refearches, He con- 
cludes his note by announcing that he hoped to be able to 
determine more accurately whether all calculi of the bladder 
were really of the fame nature. But during the cight years 
which 
