ON EVAPORATION AND DISSOCIATION. 
83 
10'3 millims. Now, as we have already shown, that with stable substances the solid 
has invariably a lower vapour-pressure than the liquid (‘Transactions,’ Part II., 1884, 
p. 461), and as from theoretical considerations this must be so; and as it is also 
evident that the melting of chloral methyl-alcoholate must be accompanied by absorp¬ 
tion of heat, for when the liquid substance is allowed to cool below its solidifying 
point, temperature rises when solidification begins; it appears to us necessary to 
account for this phenomenon by the supposition that the products of dissociation are 
soluble in the liquid, and are therefore prevented from exerting their full pressure. 
Similar phenomena have been observed with the ethyl alcoholate, and it was noticed 
that when liquefaction commenced pressure fell at once. (The curve is given in 
Plate 1.) 
§ 26. Temperatures of Volatilization of Chloral methyl-alcoholate. 
The initial pressure in the still was 2’2 millims. On heating with aniline vapour, the 
temperature gradually rose more and more slowly to 40‘6° without alteration of 
pressure. On raising pressure to 5*5 millims., the substance melted completely at once. 
The melting pressure lies, therefore, between 2*2 and 5*5 millims. Plere, again, no 
relation between temperature and pressure is observable. 
§ 27. It was noticed that the vapour-pressure of the methyl alcoholate in the 
barometer-tube was lower than that of the hydrate at the same temperatures, in spite 
of the fact that methyl alcohol is more volatile than water ; and it appeared likely 
that the substance would be more stable than the hydrate. This was found to be 
the case by the following determinations of vapour-density. It will be noticed that 
while the vapour-pressure at 78'5° is 160 millims., the density was determined at 
131*4 millims. 
Vapour-densities of Chloral methyl-alcoholate. 
W eight. 
Temperature. 
Pressure. 
Volume. 
p. y. 
Vapour- 
densiiy. 
Percentage 
Lumber of 
molecules decom¬ 
posed. 
0-0203 
O 
78-5 
millims. 
131-4 
cub. centims. 
33-53 
4406 
50-32 
per cent. 
78-06 
— 
117-0 
38-03 
4450 
49-82 
7984 
— 
132-1 
148-6 
38-01 
5648 
45-24 
100-0 
— 
JJ 
134-7 
42-28 
5695 
44-86 
>5 
1509 
37-58 
5671 
45-U6 
The theoretical vapour-density of the dissociated substance is 44*8. 
C of! TI 
§28. Chloral ethyl-alcoholate, CC1 3 .CH 4 q^ 3 5 .—Formed by direct combination 
of anhydrous chloral with ethyl alcohol. It was crystallized from its solution in 
ethyl alcohol. It is stated by Jacobsen to melt at 56° ( loc . cit.) ; by Lieben at 46° 
(‘ Berichte,’ III., p. 909 ; and we find its melting-point to be 46*5°. The boiling-point 
m 2 
