36 
BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 
duplicate commercial conditions on a laboratory scale. It was found 
that air under a pressure of 7 inches completely fulfilled this condition 
with the still that was used, and that by using this air pressure the 
creosotes made at the laboratory agreed as closely as could be 
expected with commercial oils from the same tar. Figure 15 shows 
the indices of refraction, the specific gravities, and the sulphonation 
residues of two creosotes, one made at the laboratory and the other 
at a commercial plant from tar No. 1. Figure 16 shows the index of 
refraction values and the specific gravities of another pair of creosotes 
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220 240 260. 280 300. . 320 
TEMPERATURE (NOT CORRECTED) °C 
Fig. 15.— Physical constants of two coal-tar creosotes 
produced from tar No. 1. 
Commercial coal-tar creosote — Dotted line. 
Experimental coal-tar creosote — Solid line. 
240 260 280 300, „ 320 
TEMPERATURE (CORRECTED) °C 
Fig. 16.— Physical constants of two coal-tar creo- 
sotes produced from tar No. 2. 
Commercial coal-tar creosote— Dotted line. 
Experimental coal-tar creosote — Solid line. 
produced from tar No. 2, and figure 17 shows the indices or refraction 
of two other pairs of creosotes made from tars No. 3 and 4, respec- 
tively. These figures show that creosotes can be produced from tars 
in the laboratory in such a way as to duplicate commercial condi- 
tions, and can be made as nearly identical as two analyses of the 
same oil. 
In view of the fact, however, that not all tar distillers use air in 
their operation, it was decided that all work on authentic tars should 
