204 PHILOSOPHICAL TRANSACTIONS. [aNNO ]75]. 



XXXIX. Extract of Two Letters from Dr. j4lston,* Bat. Prof, at Edinburgh, 

 to Dr. Mortin.er, Sec. R. S. The first dated ITth March, 1749; the second, 

 August g, 1750. p. 265. 



A property of quick-lime, which Dr. A. believed had not been observed before. 

 In June 1743, for some experiments in vegetation, he infused about 2 lbs. of 

 quick-lime in 24 lbs. of water, resolving to change the lime, as soon as it did 

 not communicate its virtues to the water. He soon made use of the first lime- 

 water, and filled the vessel with fresh water. When that was exhausted, he 

 filled it up a third time ; and so on for 20 or 30 times : for he had no reason to 

 change the lime for 3 years; so long it was good lime-water, gathered crusts on its 

 surface, turned syrup of violets green, vegetable infusions yellow, tasted as at first. 

 But at the end of the third year, it gathered no more crusts, was no more lime water. 



The quick-lime, which he kept dry, fell soon into a powder ; it stood covered 

 for 3 years (the vessel with the lime-water in it was an inverted large bell-glass, 

 never covered) in the green-house. This powder he infused in water, but it 

 communicated no virtue to it whatever. The calx viva that he used, was made 

 of the common limestone. It was also a common observation of our farmers, 

 that the effect of lime on lands lasts only 3 years. 



Second Letter, August Q, 1750. 



The paradox, which he formerly mentioned, concerning calx viva, which no 

 body would at first believe, he had demonstrated by repeated experiments, by 

 which it appears, that the stone calx viva may afford more than 600 times its 

 own weight of good lime-water ; for from i dr. of quick-lime he had 40 oz. of 

 lime-water ; from 1 lb. of quick-lime 500 lbs. of lime-water ; and the lime was 

 not yet exhausted, the water being as good then as at first, by every experiment 

 that he knew. He poured some of it cold (very lately) on some small calculi, 

 in a drinking glass, and in one night's time such phenomena appeared as notably 

 explained, as well as confirmed, the use of lime-water in the stone. He found 

 also, that quick-lime kept dry, in the open air, 14 months, communicated 

 nothing to water, though long infused in it ; that lime-water, boiled down to a 

 4th part, is not weakened, neither sensibly stronger ; yet yields a very little of 

 small slender prismatic crystals. 



XL. A new Trocart for the Puncture in the Hydrocephalus, and for other 

 Evacuations, which are necessary to be made at different Times. By M. le 

 Cat, F. R. S. Translated from the French by Thomas Stack, M. D., 

 F. R. S., p. 267. , .,j. 



This new trocart is represented by fig. 2, pi. 6, and has this peculiarity, that 



• Author of lectures on the Mat. Med. 2 vols. 410; for the most part a compilation from the older 

 writers, and seldom referred to in the present day. 



