COAL-TAE AND WATER-GAS TAR CREOSOTES. 
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be carried out with the use of air under a pressure of 7 inches of 
water until all the moisture had been expelled from the tar. The 
rest of the distillation was completed without the use of air. The data 
thus obtained represent creosote oils that any manufacturer could 
obtain from the same tar. If 
there is any difference, the oils 
are lower in index of refrac- 
tion and specific gravity, and 
higher in sulphonation residue 
than they would have been 
with the use of air. In other 
words, any specification that 
might result from this investi- 
gation would be on the safe 
side and would work no hard- 
ship on the manufacturer of 
creosote oil. 
It was a somewhat difficult 
matter to cut the distillates 
from the tar in such a manner 
that an oil could be obtained 
having a distillation range 
similar to that of a commer- 
cial creosote. In practice, 
therefore, no attempt was 
made to separate the light 
oils from the creosote oils in 
the distillation from the tar 
still. The only separation 
made was the fraction con- 
taining the water and the 
more volatile of the fight oils. 
The total distillate above this 
point was collected in one con- 
tainer and subsequently dis- 
tilled from an ordinary flask. 
All oil coming over below 205 ° 
C. was discarded. That boil- 
ing from 205° to 235° C. was 
collected separately. The 
residue above 235° C. was 
weighed, and to this was added 25 per cent of its weight of the frac- 
tion boiling between 205° and 235° C. In this way the creosotes were 
made to conform to specification No. 1 of the American Railway Engi- 
neering Association so far as distillation limits were concerned. 
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24-0 260 280 300 
TEMPERATURE (NOT CORRECT ED) °C 
Fig. 17.— Index of refraction values of coal-tar creosotes pro- 
duced from tars No. 3 and No. 4. 
Commercial coal-tar creosotes — Dotted lines. 
Experimental coal-tar creosotes — Solid lines. 
