CHAPTER v.— COMPARISON OF THE PROPERTIES OF COMMERCIAL 

 COAL-TAR CREOSOTES AND COMMERCIAL WATER-GAS-TAR CREO- 

 SOTES. 



It is believed that a short comparison of the properties of com- 

 mercial oils will be of value, notwithstanding the fact that they have 

 been discussed at some length in the preceding chapters. Table 30 

 shows the similarities and dissimilarities of coal-tar creosotes and 

 water-gas-tar creosotes. 



Table 30. — Comparison of the properties of commercial coal-tar creosotes and commercial 



water-gas-tar creosotes. 



Specific gravity of original creosote 



Flash point 



Burning point 



Distilling range 



Change in specific gravity per degree C 



Sulphonation residue of fractions 275° to 285° C 



Tar-acid content 



Character of hydrocarbon 



Ratio of specific gravity to index of refraction of the fraction 



275° to 285° C. 

 Toxicity 



Coal-tar creosote. 



1.01 and up 



70° C. and up 



90° C. and up 



170 to 400° C 



0.00078 



to 8 per cent 



Up tp 10 per cent 

 Chiefly aromatic . 

 1.8i 



Shown in fig. 37.. 



Water-gas-tar 

 creosote. 



1.00 and up. 



70° C. and up. 



90° C. and up. 



170 to 400° C. 



0.00078. 



to 8 per cent. 



None. 



Chiefly aromatic. 



1.56. 





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Fig. 37. — Comparison of the toxicities of coal-tar creosotes and water-gas-tar creosotes. 



The chief difference between these two classes of creosote are a 

 total lack of tar acids and bases in the water-gas-tar creosotes, a 

 higher general average of the sulphonation residues in water-gas-tar 

 creosotes than in coal-tar creosotes, and a lower toxicity. (Fig. 37.) 



The only methods known at the forest products laboratory for 

 differentiating between two classes of oils are the determination of 



77 



