RESEARCHES ON THE VOLATILE HYDROCARBONS. 165 
cooled in a mixture.of ice and salt. The retort, which stood in a small copper bath 
containing pounded ice, was charged with about 250 c.c¢. of the liquid, which had been 
previously cooled in a mixture of ice and salt. Temperature of the laboratory, 16° C. 
Observations during the distillation : — 
Temperature of the retort-bath, : : 0° 
1 “ “ boiling liquid, . : - 0°.6 
s “ vapor, ‘ 2 é 13°.5 
Temperature of the retort-bath, . c = AP 
A5 minutes later.* 2. «“ “ poiling liquid, . 1°.3, 
os “vapor, . : Fi » 12°.2 
Temperature of the retort-bath, ‘ ‘ 6° 
15 minutes later. 3. “ boiling liquid,- - 1.8 
# “ vapor, ‘ : 12°.6 
Temperature of the retort-bath, . E » 11° 
30 minutes later. 4. “ boiling liquid, . é 3°.8 
u “vapor, . 7 . « 12°.4 
“Temperature of the retort-bath, . é : 14°.5 
30 minutes later. 5. ae “ boiling liquid,. . . 7°38 
ca « vapor, ; : : 13°.8 
The apparent inconsistency that the temperature of the boiling liquid should be 
above that of the heating medium, — viz. an ice-bath — which continued during the 
first forty-five minutes of the experiment, is to be explained by the fact that there 
was a long column of mercury, above the surface of the liquid, which was subjected to 
the heating influence of the vapor. JI would further remark that the gradual elevation 
of the boiling-point, as indicated by the thermometer in the liquid, is also only appavr- 
ent, and is’ due to the gradual uncovering of the bulb as the liquid was distilled off 
At the close of the experiment only about one fifth of the bulb, which unfortunately 
was a long one, was under the surface of the liquid. That this is the true explanation 
is evinced by the fact that during the experiment not a drop of liquid was observed 
to fall back into the retort from the “elevated condenser,” although this was a tube 
ten feet in length, and cooled to the temperature of 0°. 
I will now proceed to give my determinations of the boiling-points of various 
hydrocarbons, and of some of their derivatives, and then pass directly to consider the 
bearing of these results on the question concerning the increment of boiling-point for 
* From this point the temperature of the retort-bath was gradually raised by means of a small gas-flame. 
