130 ON A PROCESS OF FRACTIONAL CONDENSATION. 
For an apparatus to stand upon the table, the safety-lamp and furnace are especially 
desirable. I have also used them for the larger apparatus, placed upon the floor of 
the laboratory. As a practical test of the security which they afford, I may relate an 
incident which happened to myself. I had left the laboratory for a short time, with 
such an apparatus in full operation; the retort containing nearly a quart of light 
petroleum boiling below 100° C. Having been detained longer than I expected, on 
returning I found the laboratory filled with the vapors of hydrocarbons; and, on 
approaching the retort, found that the caoutchouc joint, connecting the retort with 
the elevated worm, had failed, and that the larger portion of the liquid had distilled 
into the room, having been mainly condensed in the upper worm, and conducted 
thence down the outside of the retort into the safety-lamp. This process was still 
going on, the lamp being highly-heated from the excess of fuel thus added to it, but 
no ignition took place outside the lamp. Although this experiment was rather injudi- 
cious, it furnishes a valuable test of the efficiency of the safety-lamp and furnace. 
Having described the apparatus, I now proceed to give such details of the method 
of conducting the separations as have been found, in my experience, most efficient 
and economical of time. In commencing with a crude mixture of unknown liquids, 
I deem it advisable to operate at once on a tolerably large quantity of material, espe- 
cially if the constituents are supposed to be numerous, and to omit chemical treatment 
till after the separations have so far progressed as to indicate the number and species 
of bodies present, and, approximately, their several boiling-points. 
Notwithstanding the precautions taken to avoid loss from evaporation and leakage, 
I have at times been surprised at the large waste of material which has been made 
apparent after a long series of operations. When it is considered, however, that the 
time required to make a complete separation of a very complex mixture of liquids 
must necessarily be very protracted, during which more or less of evaporation is con- 
stantly taking place, it will be a matter of no surprise that the loss is so considerable. 
The quantity of material required must depend also on the proportions in which the 
various constituents are contained in the crude mixture, and upon their degree of 
volatility ; but as these cannot be known @ priori, it may suffice to make a single pre- 
liminary distillation of a portion of the mixture, from a tubulated retort, to ascertain 
the range of temperature within which it distills, noting at the same time the propor- 
tions which come over between certain temperatures ; as, for example, below 50° C.; 
between 50° and 100°, ete.; from these data one may judge pretty nearly of the 
quantity which it will be advisable to take. It is evident that, when very volatile 
