O^ EVAPORATION. • ' Y 



ther at the fop, and the extremities bent into a hook, by which 

 the veflel might be fufpended from the end of a balance, &c. 

 This done, the velTel was nearly filled yv'ith water, which 

 was then made to boil over a fmall red fire in different circum- 

 ftances: it was held in the hand and removed nearer to or fur- 

 ther from the fire, fo as to be kept juft at the point of ebullition. 

 In this (late the veffel and water were weighed true to a grainj 

 and the inftant of time noted by a watch; then kept as above 

 at 212° for ten minutes or more and again weighed: and the 

 lofs of water by evaporation, per minute, was thus afcertained. 

 The experiments were repeated feveral times in the fame as 

 well as in different circumftances ; and the refults in no inftance 

 differed materially when obtained in the fame circumllances. 



The leaft evaporation per minute was 30 grains: this was— which was 



when the fire, or lamp, was in the middle of a room, the doors /^* ^^^P '^K 

 ' '^ \ , . . furroundmg air 



and wmdows (hut, and the air calm. was ftilleft. 



The next degree was 35 grains per minute or thereabouts : —and gradually 

 this was when the evaporating veffel was over a fmall fire in™°^*' 

 the ufual fire-place; there being a moderate draught of air, 

 and the room clofe, 



A britker fire, caufing a ftronger current of air up the chim- —the more ^ 

 ney, gave from 35 to 40 grains per minute. waJthCedf 



When the windows of the room were open, and a firong 

 wind prevailed, the draught over the fire was proportionally 

 increafed, and the evaporation was from 40 to 45 grains per 

 minute. 



The extremes that have thus been noticed are 30 and 45 

 grains per minute: but were the experiment tried in the open 

 air in high winds, I am inclined to believe from a comparifon of 

 the obfervatlons, that an evaporation of 50, 55 or even 60 grains 

 per minute might be obferved. 



On the Evaporation of Water below 212*. 

 I have frequently tried the evaporation at all the temper- Water at tem- 



atures below 212° : it would be tedious to enter into detail of P"^^""^'^ ^^^^^^ 



112* ioft by 

 all the experiments, but ihall give the refults at fome remark- evaporation.— i 



able points. In all the high temperatures I ufed the veffel 



above mentioned, keeping a thermometer in it, by which I 



could fecure a conftant heat, or at leaft keep it ofcillating 



within narrow limits. 



Tha 



