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X. Intelligence and Miscellaneous Articles, 



RESEARCHES ON THE ABSORBING-ACTION WHICH CERTAIN VO- 

 LATILE LIQUIDS AND THEIR VAPOURS EXERT ON THE HEAT 

 FROM A LAMP WITH A GLASS CHIMNEY. BY M. P. DESAINS. 



V ASK leave from the Academy to communicate the results of a 

 ■*■ series of experiments which I have undertaken with the view of 

 studying the comparative actions which a very volatile liquid and its 

 vapour exert under comparable conditions on the same calorific ra- 

 diation. 



I worked with ordinary ether, formic ether, and bisulphide of 

 carbon. The source of heat was a lamp with a glass chimney. The 

 first two of these substances exercise a considerable absorption on 

 the radiation from the lamp ; and, comparing the manner in which 

 they act under the two physical conditions, I found that a column 

 of a given weight and section of each of these substances exercises the 

 same radiation and absorption, the intensity of which is independent 

 of the physical condition of the medium. The liquid column is very 

 short, and that of the vapour very long, but they produce the same 

 effect. 



To prove this fact, I took (1) a copper tube blackened inside, about 

 a metre long and a decimetre in diameter ; it is closed by glass plates, 

 and provided with stopcocks and with a jacket by means of which 

 water can be kept at a given temperature ; (2) a trough closed by 

 clear glass, having the same section as the tube, and such a thickness 

 that the quantity of liquid which can fill it is not enough to produce 

 as much vapour as would saturate the tube at the temperature at 

 which it is to be worked. The tube and the trough being ready, are 

 placed behind each other, their axes being in the same right line. 

 The tube is heated to a suitable temperature, 38° for ordinary 

 and 57° for formic ether; the air is expelled and a small quan- 

 tity of vapour is formed, so as to have an internal pressure of a 

 few centimetres ; and then the source of heat is allowed to radiate 

 through the system of the tube, the empty trough, and the lenses, 

 whose object is to increase the thermoscopic effect. The thermo- 

 scopic action is measured. Let D be this value after making all 

 corrections. The experiment is recommenced after filling the tube 

 with ether. A considerably smaller action is observed, which I call 

 D'. The difference arises from the absorption which the liquid ether 

 exerts on the radiation. That being done, the ether of the trough 

 is brought into the tube and the trough replaced in its original posi- 

 tion. When vaporization has taken place, it is ascertained whether 

 the glasses have remained perfectly bright. Care is also taken that 

 the pressure in the tube is less than that of saturation; and the ther- 

 moscopic action is measured afresh. 



It is found that it is virtually equal to D', which establishes the 

 truth of the proposition announced. 



The following are a few numbers. 



