50 Mr. Daniell on Evaporation. 
mixture of pounded ice and muriate of lime, to the exterior ball of 
the hygrometer. In this manner the interior ball was cooled to 
0°, without the appearance of any dew. The temperature of the 
water and air were, in this instance, 58°, and the pressure of the 
atmosphere 30°5. 
From this experiment it appears, that in the arrangement above 
described, the surface of water was not adequate to maintain an 
atmosphere of the small elasticity of °068 inch; in other words, 
the degree of moisture in the interior of the receiver could not 
have exceeded 129, the point of saturation being reckoned 1000. 
How much less it was than this, or whether steam of any less de- 
gree of elasticity existed, the experiment, of course, did not deter- 
mine. We may reckon, however, without any danger of error in 
our reasoning, that the sulphuric acid, under these circumstances, 
maintained the air in a state of almost perfect dryness. 
Experiment 2, 
The same trial was made with atmospheres variously rarefied, by 
means of the pump. No deposition of moisture was, in any case, 
perceived with the utmost depression of temperature, which it was 
possible to produce; and the state of dryness was as great, in the 
most highly attenuated air as it was in the most dense. In the 
higher degrees of rarefaction, the water however became frozen. 
Experiment 3. 
The water, which had been previously exposed to the yacuum of 
the pump to free it from any air in solution, was weighed in a very 
sensible balance, before it was exposed to the action of the sulphu- 
ric acid under the receiver. Its temperature was 45°, and the 
height of the barometer 30°4. In half an hour’s time, it was again 
weighed, and the loss by evaporation was found to be 1'24 grains. 
It was replaced, and the air was rarefied till the gauge of the pump 
stood at 15-2; in the same interval of time it was re-weighed, and 
the loss was 2°72, but its temperature was reduced to 43°. The 
loss from evaporation, in equal intervals, with a pressure con- 
stantly diminishing one-half, was found to be as follows:— 
