116 
PROFESSOR W. RAMSAY AND DR. S. YOUNG 
§75. Discussion of Results. 
For the sake of clearness we tabulate the results already described :— 
Name of subslance. 
Vapour-density shows— 
Temperature of volatilization. 
Vapour-pressure, or 
pressure of dissociation. 
Chloral hydrate .... 
Dissociation almost com¬ 
plete at 78° 
Independent of pi’essure 
Curve of ordinary 
form. 
Butyl chloral-hydrate . 
Complete dissociation at 
160° 
Independent of pressure 
Curve of ordinary 
form. 
Chloral methyl-alcoholate 
At 78 ' 5 °, about 78 per cent, 
dissociated 
Independent of pressure 
Curve of ordinary 
form. 
Chloral ethyl-alcoholate . 
At 78°, 82'5 to 83 per cent, 
dissociated 
Independent of pressure 
Curve of ordinary 
form. 
Ammonium carbamate 
Total dissociation . 
Constant at about 65° 
under all pressures 
Curve of ordinary 
form. 
Ammonium chloride . 
Dissociation very nearly 
complete at 280° 
(Curves 
identical.) 
Phthalic acid. 
Vapour-density not deter¬ 
mined; dissociation pro¬ 
bably very large, no 
constant melting-point 
Rudimentary curve at 
low pressures 
Abrupt change of 
direction of curve. 
Succinic acid. 
Vapour-density not deter¬ 
mined; dissociation pro¬ 
bably less complete than 
with phthalic acid, con¬ 
stant melting-point 
Curve more obvious than 
with phthalic acid 
Appears to depend 
on amount of 
substance pre¬ 
sent ; curve shows 
double flexure. 
Aldehyde-ammonia. 
70 per cent, dissociated at 
78" 25°, under reduced 
pressure 
Curve of usual form . 
Curve of usual 
form, but pres¬ 
sure higher than 
by other method. 
Paraldehyde. 
No dissociation .... 
(Curves 
identical.) 
Metaldehyde. 
Equilibrium estab¬ 
lished only after 
very prolonged 
heating. 
Nitrogen peroxide . 
Dissociation small below 
20° 
Vapour - density abnor¬ 
mally high, especially 
at low temperature 
No results 
No results 
(Curves 
identical.) 
Acetic acid. 
Ethylamine hydrochloride 
Chlorine hydrate 
(Curves 
identical.) 
§ 76. It is evident that these substances may be divided into two groups : that in 
which the curves representing temperatures of volatilization and vapour-pressures are 
identical; and that in which these curves are distinct. The members of the first 
class behave like ordinary solids and liquids; and the class includes the three sub- 
stances, ammonium chloride, nitrogen peroxide, and acetic acid; wdth the first of 
these dissociation is nearly complete sixty degrees below the temperature of volatili¬ 
zation under normal pressure; with the second dissociation amounts to less than 
20 per cent, at its boiling-point; while with acetic acid it is uncertain whether true 
dissociation takes place. The second group, which contains the rest of these sub¬ 
stances, with the exception of paraldehyde, which is stable, may be divided into two 
