392 A Memoir on the Uric Acid. 
treatment of the dry extract of urine.(a) 
Hoffman, having placed a fragment of a stone 
from the kidney upon a red hot coal, found 
that it emitted a smell of ‘volatile alkali, and 
left a portion of charcoal, which was perfectly 
tasteless. He ascertained, also, that the same 
substance was very sparingly soluble in water, 
and not at all in sulphuric or muriatic acids 
at common temperatures ; but that hot nitric 
acid acted upon it, and gave a solution, which 
was not precipitated by carbonate of pot-ash. 
Hence he concluded, with reason, that con- 
cretions of this kind donot consist of calca- 
reous earth.(b) Slare, in order to shew that 
the stone of the bladder is not tartar, sub- 
mitted it to destructive distillation, and ob- 
tained oil, volatile alkali, and a brown and 
bitter salt. ‘A coal remained, which was 
nearly consumed by burning it with free ac- 
cess of air.(c) Dr. Hales, in addition to the 
same condensible products, collected. a large 
quantity of permanent gas, amounting to 516 
cubical inches, from a quarter of a cubical 
inch of the stone. He denies the power of 
dissolving calculus, not only to the sulphuric 
acid, but to alkaline salts ; evidently in con- 
(a) De Lithiasi, cap. v. § 9. Amst. 1648. 
(b) Obs. Phys. et Chem. lib. ii. obs. 25. Genev. 1748. 
(c) Lowthorp’s Abridgment of the Phil. Trans. iii. 179. 
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