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EVAPORATION IN VACUO. 
Some account of experiments in France , in prosecution 
of Professor Leslie's discovery of the method of con- 
gelation by means of a vacuum . 
It will be proper to give some previous account of 
what has already been done by professor Leslie, before I 
introduce the following paper from the Journal de Phy- 
sique, of October 1812. 
The effects of evaporation in producing cold have long 
been known. Dr. Cullen and Dr. Bryan Higgins applied 
ether for this purpose by moistening slowly the bulb of 
a thermometer. Higgins, by this method, reduced the 
mercury to 40 of Fahrenheit. Cavallo invented a very 
simple and ingenious apparatus for freezing by means of 
ether. 
In 1795 Mr. Oliver Evans suggested the possibility 
of freezing water by means of evaporation of ether in 
vacuo, but he does not appear actually to have made the 
experiment, though he has suggested the means. 
In 1810 or very early in 1811, Professor Leslie, in 
making some experiments in relation of air and mois- 
ture, succeeded in freezing water in vacuo, by causing 
the vapour raised from the water to be absorbed by 
strong sulphuric acid, the water being contained in a 
small shallow dish about two inches above the surface 
of the acid : and in the beginning of 1812 by means of 
an apparatus connected with an excellent air pump, he 
succeeded in freezing mercury, by moistening the bulb 
of a thermometer with water, repeatedly, until the effect 
was produced. £>oon after his first experiment, he pro- 
posed to apply the principle in the large way to the pro- 
duction of ice, the concentration of juices, the drying of 
gunpowder, &c. 
In 1811 M. M. Clement and Desormes, in France, 
proposed also the application of the same principle to the 
