ON THE BOILING OF MIXED LIQUIDS. 235 
caoutchouc, but this last changes constantly its boiling point, 
when it is by itself. The few volatile oils heavier than water 
have a specific gravity so little different from that of water, 
that some are carried up in mass by boiling, whilst the others, 
as the oil of the pinks, becomes at a certain temperature even 
lighter than water. 
The vapors of two liquids which in a state of complete 
fluidity do not commingle, behave very differently from those 
which in that state do mix together. It is known that such 
mixtures constantly change their boiling point, according to 
the change in proportion between the liquids. The tempera- 
ture of their vapors is always the same as that of the liquid, 
and varies with it. But as the temperature of the boiling li- 
quid is always more elevated than the boiling point of the more 
volatile liquid, the temperature of the vapor will therefore be 
more elevated than that at which the sum of the maxima of 
elasticity of the two vapors is equal to the atmospheric pres- 
sure. It follows that the vapors of one of the liquids, and 
probably of both, are not at their maximum of elasticity. 
If we introduce a liquid such as ether into the empty space 
of a barometer tube, and if, after having observed the maxi- 
mum of elasticity of the vapor at the common temperature, 
we add another liquid capable of mixing with the ether, such 
as alcohol, and whose vapor has less elastic force, the elasti- 
city of the vapors of the two liquids will be weaker than that 
of the ether alone, and it will diminish in proportion as the 
alcohol is increased; so that with a large proportion of alcohol 
for the same quantity of ether, the elasticity will be the same 
as that for alcohol at the common temperature of observation. 
The same happens if, in place of alcohol, we take the oil of 
turpentine, and in place of ether the carburet of sulphur, or 
the oil of caoutchouc, or again, if we introduce first water, 
then alcohol. In these experiments, which were made at 
17°.5 C.j there was in the tube so much liquid that a portion 
remained in a liquid state. If this had not been so, the results 
would have been very different; for M. Gay Lussac has shown 
that at a temperature over 100° C, and at which the two are 
