r ^8r ] 



other : this I have done, and found the lofs in vacuo inrompara- 

 biy greater than that in open air ; the difFerciice however I cannot 

 now ftate, having loft the noLe I took of it. Mr. Watt has 

 fhewn, that water boils in vacuo at a degree of heat little 

 fuperior to that of the human body, and diftills as faft as it does 

 in open air at 212**, i Mem. Manchefter, 390. Water has alfo 

 been diftilled in vacuo by Wallerius, 11 Colled. Acad. 166, &c. 

 and by the immortal Lavoifier, Mem. Par. 1770, Hence in 

 nature water evaporates more when the barometer is low than 

 when it ftands high, and confequently diftillation may be car- 

 ried on on the tops of mountains more readily, and with lefs 

 heat, than at the level of the fea. 



According, to Mr. Cavendifh, water heated to 72*^ is not 

 (fuddenly) converted into vapour under an exhaufted receiver, 

 until the preffure is no greater than about ^ of the ufual pref- 

 fure of the afmofphere, that is about three-fourths of an inch ; 

 and if the water be heated only to 41, the preffure rauft be re- 

 duced to one-half an inch, but the vapours thus raifed are im- 

 mediately turned back into water on reftoring the preffure of 

 the atmofphere, Phil. Tranf. 1777, 622. But it is plain that he 

 means, that the greater part only is re-converted into vapour 

 (unlefs the air is already faturated) by the increafed preffure ; 

 for he allows that water expofed to the open air will evaporate at 



any 



