EADIATION OF HEAT BY GASES AND VAPOUES. 
17 
effected by vapour possessing one inch of tension, the same deviation from proportion- 
ality is observed. 
By mercurial gauge. 
Tension. Absorption. 
^ inch 14-8 
1 inch 18‘8 
These numbers simply express the galvanometric deflections, which, as already stated, 
are strictly proportional to the absorption as far as 36° or 37°. Did the law of propor- 
tion hold good, the absorption due to 1 inch of tension ought of course to be 29-6 
instead of 18*8. 
Whether for equal volumes of the vapours at their maximum density, or for equal 
tensions as measured by the depression of the mercurial column, bisulphide of carbon 
exercises the lowest absorptive power of all the vapours which I have hitherto examined. 
For very small quantities, a volume of sulphuric ether vapour, at its maximum density 
in the measure, and expanded thence into the tube, absorbs 100 times the quantity of 
radiant heat intercepted by an equal volume of bisulphide of carbon vapour at its maxi- 
mum density. These are the extreme limits of the scale as far as my inquiries have 
hitherto proceeded. The action of every other vapour is less than that of sulphuric 
ether, and greater than that of bisulphide of carbon. 
A very singular phenomenon was repeatedly observed during the experiments with 
bisulphide of carbon. After determining the absorption of the vapour, the tube was 
exhausted as perfectly as possible, the trace of vapour left behind being exceedingly 
minute. Dry air was then admitted to cleanse the tube. On again exhausting, after 
the first few strokes of the pump a jar was felt and a kind of explosion heard, while 
dense volumes of blue smoke immediately issued from the cylinders. The action was 
confined to the latter, and never propagated backwards into the experimental tube. 
It is only with bisulphide of carbon that this effect has been observed. It may, I 
think, be explained in the following manner : — To open the valve of the piston, the gas 
beneath it must have a certain tension, and the compression necessary to produce this 
appears sufficient to cause the combination of the constituents of the bisulphide of 
carbon with the oxygen of the air. Such a combination certainly takes place, for the 
odour of sulphurous acid is unmistakeable amid the fumes. 
To test this idea I tried the effect of compression in the air-syringe. A bit of tow or 
cotton wool moistened with bisulphide of carbon, and placed in the syringe, emitted a 
bright flash when the air was compressed. By blowing out the fumes with a glass tube, 
this experiment may be repeated twenty times with the same bit of cotton. 
It is not necessary even to let the moistened cotton remain in the syringe. If the 
bit of tow or cotton be thrown into it, and out again as quickly as it can be ejected, 
on compressing the air the luminous flash is seen. Pure oxygen produces a brighter 
flash than atmospheric air. These facts are in harmony with the above explanation. 
MDCCCLXI. D 
