18 Dr. Pearson's Experiments and Observations 
water. M. Fourcroy also says, he found magnesia in the 
intestinal calculus of a horse ; which calculus was a triple com- 
bination, of one part of phosphate of ammoniac, two parts of 
magnesia, and one of water, besides traces of animal and 
vegetable matter. 
Dr. Link, in a very elaborate dissertation, published at Got- 7 
tingen, in 1788, on urine and calculi, concludes that urinary 
concretions consist of phosphoric acid, lime, ammoniac, oil, the 
bases of different kinds of gazes, together with the acid sublimate 
of Scheele, although he did not succeed in obtaining it. 
It is a proof of Dr. Black's sagacity, that he should have 
been able to perceive, from a few experiments, that urinary 
concretions consisted of animal matter and the earth of bone, 
before the composition of this earth was demonstrated by Gahn. 
In this historical sketch it should be noticed, that alkaline 
substances, though used by the Greek physicians, and after- 
wards by the alchemical physicians, appear to have been laid 
aside by the regular practitioners, for a century or two prece- 
ding their revival, by the famous Mrs. Stephens, in 1720. 
Her prescription brought into vogue the theory of these me- 
dicines operating by their causticity. The successful use, by 
Mr. Colborne, of potash saturated with carbonic acid, ac- 
cording to the discovery of Bewley and Bergman, and the 
still further improvement in practice, from the use of soda, as 
well as potash, super-saturated with carbonic acid, by the dis- 
covery of a peculiar method by Mr. Schweppe, have com- 
pletely refuted the theory of the agency of alkalies on the 
principle of causticity. 
It appears, from the preceding brief history, as well as from 
the confession of the latest and best writers, that the expert- 
