ON EVAPORATION AND DISSOCIATION. 
85 
Here, again, the pressures in the solid are higher than in the liquid state, and 
probably for the same reason. On referring to the curve in Plate 1 it will be noticed 
that that portion representing the pressure in contact with liquid below the melting- 
point is continuous with that above the melting-point; whereas the pressure of the 
vapour in contact with solid is somewhat irregular, as is also the case with the methyl 
compound. 
§ 31. Temperatures of Volatilization of Chloral ethyl-alcoholate. 
Series I.—The initial pressure was 2 millims. ; the temperature of the alcoholate, 
heated by aniline-vapour, rose more and more slowly until it reached 47' 7°. The 
pressure was then raised to 8T millims., when the substance melted. 
Series II.—At a pressure of 2‘55 millims. the temperature rose to 47°; air was 
admitted so as to raise the pressure to 6 1 millims., the alcoholate at once melted, and 
did not re-solidify on reducing pressure to 5T millims. It was thus impossible to 
detect any relationship between temperature and pressure. 
§ 32. Vapour-densities of Chloral ethyl-alcoholate. 
Weight. 
Temperature. 
Pressure. 
Volume. 
P. V. 
Vapour- 
deusity. 
Percentage 
number of 
molecules decom¬ 
posed. 
grm. 
O 
millims. 
cub. centiins. 
per cent. 
0-02066 
78-35 
Ill 
38-42 
4265 
52-88 
82-68 
137-7 
36-28 
4270 
52-82 
82-89 
122-9 
34-68 
4262 
52-95 
82"44 
It is thus evident that this body is not wholly dissociated at 78‘35° when the 
pressure bears the ratio to that of saturation of 111 or 123 to 130. 
We propose to study in greater detail the dissociation of these interesting 
substances, as revealed by their vapour-densities; these determinations, however, 
suffice to show that they are capable of existing partially undissociated. 
§ 33. Ammonium Carbamate .—The formula of pure ammonium carbamate is 
CojoNH ’ but f rom nature of our experiments we were compelled to use the 
commercial salt, the composition of which is variable. 
The dissociation pressures of this substance have been very accurately determined 
by Naumann ( { Berichte,’ 1871, p. 782); by Isambert (‘ Comptes Bendas,’ 97, 
p. 1212); and by Motessieir and Engel (‘Comptes Kendus,’ 93, p. 595). As the 
results of all three observers agree with each other, a redetermination was unnecessary. 
Suffice it to say that they give a regular curve of the usual form, reproduced in Plate 1. 
It is also known from numerous experiments by Naumann (‘ Annalen,’ 160, p. 5, and 
