CHAPTER IV. COMPARISON OF THE PROPERTIES OF AUTHENTIC COAL- 
TAR CREOSOTES WITH THOSE OF AUTHENTIC WATER-GAS-TAR 
CREOSOTES. 
The following curves show the similarities and dissimilarities of the 
physical properties of all coal-tar creosotes and all water-gas-tar 
creosotes tested. Figure 25a shows the index of refraction plotted 
against temperature, in which the lines sloping to the left represent 
water-gas-tar oils and the lines sloping to the right represent coal-tar 
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Fig. 25.— Comparison of the physical and chemical properties of the fractions of authentic coal-tar creosotes 
and authentic water-gas tar creosotes. 
A. Index of refraction values. 
B. Specific gravity values. 
C Sulphonation values. 
• 1. Ranges of coal-tar creosotes. 
2. Ranges of water-gas tar creosotes. 
creosotes. Figure 25b shows the same thing for specific gravity, 
and figure 25c represents the sulphonation residues (but the lines in 
this case are reversed). It is apparent from these curves that there 
is no sharp line of demarcation between the physical constants of 
coal-tar creosotes and of water-gas-tar creosotes. It is to be noted, 
however, that, whereas the larger number of coal-tar creosotes have 
a sulphonation residue of less than 3 per cent (see p. 20), the larger 
number of water-gas-tar creosotes have more than 3 per cent sulphona- 
tion residue in one or more of their fractions. 
Figure 26 shows the index of refraction values of the fraction 
285° to 295° C. taken from 17 coal-tar creosotes and 14 water-gas-tar 
creosotes, plotted against percentage of sulphonation residue for the 
44 
