Vapours of Boiling Saline Solutions. • 485 



meter (No. 2) was heated in an air-bath to 125° ; and the cork /' 

 being removed, the thermometer was instantly inserted in its 

 place. The thermometer fell rapidly to 100°'5, and then began 

 to rise slowly; in two minutes it had risen to 102 o, 5. It was 

 deduced from this, that the real temperature of the steam was 

 most probably 100°, and that radiation produced some effect on 

 the dry thermometer, though apparently trifling as compared 

 with the direct thermic action of the steam. The effect of 

 radiation was also noticed on thermometer No. 1, wdiich slowly 

 fell about half a degree, apparently from the proximity of the 

 colder dry thermometer No. 2. 



Here we have two thermometers in conditions apparently 

 equal at the moment when the falling temperature of No. 2 had 

 reached the point of 109°, or, more correctly, when the tempe- 

 ratures of the two thermometers exactly coincided, excepting that, 

 while No. 2 is dry, No. 1 is supposed to be wet with saturated 

 brine. It must have remained thus wet when the brine in which 

 it was at first immersed was drawn off to the lower level h; and 

 being then at a temperature corresponding precisely with the 

 boiling-point of the liquid, surrounded by an atmosphere of sa- 

 turated steam* continually forming from the same boiling liquid 

 below, and comparatively isolated from other sources of heat or 

 cold, it could neither evaporate any of its own surrounding film 

 of brine, nor yet condense any of the steam in which it was enve- 

 loped. The surfaces of the walls b would be in the same circum- 

 stances, and consequently might be supposed to remain wet with 

 a film of brine at 109° as long as the surrounding conditions 

 remained constant. It was seen from the first experiment that 

 the thermometer No. 1 remained at the constant temperature of 

 109° in an atmosphere of steam which the second experiment 

 proved to be at the temperature of about 100°. The thermo- 

 meter No. 2 was carefully observed to have a temperature of 118° 

 at the moment it was fixed in the neck /' of the cover ; and it 

 not only fell rapidly to 109°, but continued to descend quickly 

 to near 100°, the fraction of a degree above this point being evi- 

 dently due to the heating effects of radiation acting at the same 

 time with the cooling influence of the steam. Here thermometer 

 No. 2 comports itself as the thermometer is supposed universally 

 to do ; that is, it equalizes its temperature with that of the me- 

 dium in which it is immersed; but the first experiment shows 

 clearly that if the thermometer No. 2 were now lowered by sli- 

 ding its stem through the cork until it dipped into the boiling 

 brine below (the screen n being supposed to be removed to allow 



* Assumed to be so because ascertained to be of the temperature of 100° 

 nearly, under atmospheric pressure. 



