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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240 260 280 300 320 



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20 240 260 280 300 320 



B 



Fig. 25. — Comparison of the physical and chemical properties of the fractions of authentic coal-tar ere 3sotes 

 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 



