C. M. Warren on the Volatile Hydrocarbons. 221 
the upper extremity of the mercurial column. And, as usual, 
4 paper screen, closely fitting the thermometer, is placed across 
from the direct influence of the ascending heat. . 
I have observed that it often requires considerable time—va- * 
Tiable according to its length and the thickness of the glass spin- a 
dle—for that part of the thermometer above the retort to acquire 
the highest temperature which the boiling liquid can communi- a 
fate to it. During this time the thermometer evidently is not in 
a fit state for an observation. While this gradual change in the 
condition of the thermometer is taking place, it is desirable, for 
Obvious reasons, that no vapors should escape from the retort. 
I therefore proceed as follows. The retort, the neck of which 
has previously been wrapped with a wet cloth, is placed in such : 
4 position that the neck shall slightly incline towards the peer i 
of the retort. If necessary, some pieces of ice, which will ad- 
here firmly to the cloth, may be laid along the neck to insure 
Complete condensation of the vapors during ebullition. While 
_ the retort is in this position, ebullition is continued for consider- 
able time, until it ceases to have any effect on the height of the 
Mercury in the thermometer.. The lamp being now removed for 
the moment, the neck of the retort is turned down, and quickly 
e lamp being now re- 
ch cases I have generally taken . ae 
8 Corresponding to the longest interval of time, ag prow 
eo ” Poggendorff’s Annalen, 1847, lxxii, 38.0 
