132, ON A PROCESS OF FRACTIONAL CONDENSATION. 
first indication of choking of the worm is a partial or entire stoppage of the strea: 
liquid which normally flows steadily from the end of the worm into the retort. 
interruption or unsteadiness of this flow would indicate too rapid ebullition. 
As a rule, other things being equal, the greater the difference between the 
perature of the bath and that of the retort, the slower the products will come 
and the more effectual will be the separation. I think it possible, however, that 
earlier fractionings may be conducted so slowly that the loss of time would r 
than counterbalance what might be gained by more thorough separation, and 
equally good results may be more economically obtained by more frequent operat 
somewhat more rapidly conducted. 
A striking illustration of the advantage to be gained by this process is presente: 
the fact that, during the first fractioning of a crude mixture, such as American pt 
leum or coal-tar naphtha, for example, the difference between the temperature of 
bath and that of the retort may sometimes be as much as 35° C., or even more. W 
as the products become purer, this difference between the temperatures of the | 
and retort proportionally decreases, till finally, in operating on a pure product, 
temperature of the bath must be brought to within a few degrees of that of the re 
in order to bring the vapors through. But the amount of this difference is vari 
for different bodies of equal purity. 
These first fractionings must necessarily be quite arbitrary; for, as a general 1 
when operating on such mixtures as those just mentioned, neither the thermom 
nor the quantities obtained for any given range of temperature will indicate 
decided preponderance of any one substance. On the contrary, the temperature 1 
uniformly, and about the same quantity is generally obtained for the same numbe 
degrees of temperature throughout the operation. In other mixtures, in which cer 
bodies may seem to be present in much larger proportion than others, or in which tl 
may be a greater difference between the boiling-points of the constituents than in 
cases referred to, — facts which would be indicated by the thermometer of the re 
and by the relative quantities of the products obtained, — there might be sometl 
gained by exercising discretion in taking off fractions according to these indication 
In the second series of fractioning, the first or lowest fraction of the preceding se 
which is large enough to operate upon by itself, is transferred to the retort, and broi 
into ebullition. The temperature of the bath is thegyadjusted as above described, 
the distillation continued, the fractions obtained being placed in their appropriate 
tles until the temperature of the retort shall have risen to, or somewhat above, 
point at which the second or next succeeding fraction of the first series may be 
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