as 
( 285 ) 
The boiling points of the mixtures were next determined at a 
pressure of 1 atmosphere and the composition of the vapour of these 
boiling mixtures was also determined by means of a special apparatus. 
The former form the line “HG, the latter the line #/G of which 
the following points are the most important: 
F 20.7 boiling point of acetaldehyde 
I 41.7 vapour 2.5 °/, paraldehyde 
ER ek 7 liquid — 33.5. 4 1 
G 123 .7 boiling point of paraldehyde. 
On account of the great difference in volatility of the two components 
the liquid- and vapour lines are situated far from each other. The 
vapour of a boiling mixture is much richer in acetaldehyde than 
the liquid, for which reason the two are readily separated by 
fractionation. 
In the third place the critical temperatures of the components and 
of a few mixtures were determined. (Only that of acetaldehyde had 
been previously found by Prof. van per Waats to be 184°). 
Result : 
Critical temp. */, Paraldehyde. 
te TSS" 0 
Brel Me 11.0 
Q 241° 22.0 
IN A70 50.0 
M 286° 100.0 
These are the relations when there is no transformation of acetal- 
dehyde into paraldehyde, or the reverse. 
If, however, a trace of a catalyzer is added, acids in particular, the 
two molecules can be converted into each other, till the condition of 
equilibrium corresponding to p and ¢ has been reached *). 
It appeared that by these means the boiling point of all mixtures 
came in a very short time to 41°.7 and as this point according to 
the line HG is situated at 53.5 °/, of paraldehyde, it represents 
the relation of equilibrium in the liquid condition at that temperature 
and 1 atm. pressure. As the corresponding vapour according to 
point J of the vapour line FJG only contains 2.5 °/, of paraldehyde 
a rational explanation has thus been found of the long-known fact 
1) A little meta-aldehyde is also formed but the quantity remaining in solutior 
is so very trifling that its influence on the system considered may be utterly ne- 
elected. It must still be ascertained what place meta-aldehyde occupies in regard 
to the two forms at high temperatures. 
