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| A Memoir on the Urie Acid. 895 
The next series of experiments on the lithic 
acid, were published by Mr. Higgins of 
Dublin; (h) and these were soon afterwards 
followed by the researches of the late Dr. 
Austin. (ij) The mode of investigation, 
adopted by both these philosophers, was 
chiefly that of destructive distillation. Little, 
therefore, was added to our knowledge of the 
subject, except the discovery, by Mr. Hig- 
gins, that nitrate of ammonia is produced by 
the action of nitric acid on this variety of 
calculus; and a more accurate .examination, 
by Dr. Austin, of the permanently elastic 
fluids. . 
In the year 1793, Mr. Murray Forbes, in 
an ingenious treatise on Gravel and Gout, (/) 
pointed out a mode of separating the lithic 
acid from urine, which has the merit of great 
simplicity and efficacy. It consists in adding 
diluted sulphuric acid, to recently voided 
urine (in the proportion of about 20 drops of 
the former, tohalf a pint of the latter,) and 
in allowing the mixture to stand about 24 
hours. At the expiration of that time, small 
(h) Compar. View of the Phlogistic & Antiphlog. 
Theories, p. 283. 
(i) Treatise on the Origin and component parts of the 
Stone of the urinary bladder, 1791. 
(k) Published in 8yo. at London, 1793. 
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