( 286 ) 
that on distilling paraldehyde with a little sulphuric acid, nearly pure 
acetaldehyde is collected. 
At temperatures below 41°.7, the equilibrium appeared to be dis- 
placed along the line HL, which at 6°.8 and 88.1 °/, of paralde- 
hyde meets the melting point line of paraldehyde. 
The consequence is that, from whatever mixture we may start, 
paraldehyde will always erystallise out on adding a trace of sulphuric 
acid and cooling to 6°.8 and as the transformation of acetaldehyde 
into paraldehyde proceeds very rapidly even at this temperature, the 
whole mixture becomes at last a solid mass of paraldehyde. This 
even proved to be the case when pure acetaldehyde was taken as 
starting point. On the other hand paraldehyde in the presence 
of a trace of a catalyzer does not melt at 12°.5 but at 6°.5 owing 
to partial conversion into acetaldehyde. 
We have no knowledge of the equilibrium in the vapour at these 
low temperatures but something can be said regarding higher tem- 
peratures. 
The lines FL HG and F/G have regard to 1 atm. pressure. Simi- 
lar lines might however, be determined for a higher pressure and 
in that manner the displacement of the points A and / with the 
pressure would be determined. Finally, we should thus arrive at 
the critical line ZM and here the compositions of the vapour and 
liquid, which indicate the relation of equilibrium, must become the 
same. It appeared from a series of determinations that the point P 
at 224° and 11°/) of paraldehyde is this very point. 
At these high temperatures, the equilibrium is also reached after 
some time without a catalyzer. 
It appears from the position of P that the line which gives the com- 
position of the liquid when equilibrium is attained slopes in the begin- 
ning very rapidly, with rising temperature, towards the acetaldehyde 
side of the figure (portion “7H A)*) but afterwards much less rapidly. 
The line of equilibrium of the vapour certainly does retrograde, 
for at 41° the vapour still contains 2.5°/, of paraldehyde, at 100° 
less, and at 221° again 11°/,. In this case the influence of the pres- 
sure prevails obviously. As paraldehyde is a triple polymer, the 
influence of the pressure is very marked. 
If we make a representation in space of the whole figure, like the 
one mentioned in the previous Communication, it will be noticed that 
the equilibria where the possibility of the mutual transformation of 
acetaldehyde and paraldehyde is admitted, are lines on the surface 
1) The point K has been determined by TurBaBa at 50°.5 and 39.40/,. 
