CHAPTER IV. COMPOSITION AND PROPERTIES OF WATER-GAS-TAR 



CREOSOTES. 



COMPOSITION OF WATER-GAS-TAR-CREOSOTES. 



The distillate oils of water-gas tar boiling above 200° C. and as 

 high, sometimes, as 400° C. are referred to as water-gas-tar creosotes. 

 Like the coal-tar creosotes, they are extremely complex mixtures, 

 composed chiefly of compounds of the aromatic series. They usually 

 contain compounds of the aliphatic series, but this is by no means a 

 characteristic of all water-gas-tar creosotes. The amounts may vary 

 from nothing to as high as 20 or 25 per cent, depending chiefly on the 

 temperature of formation of the mother liquor, tar. The results of 

 much less research work have been published on water-gas tar and 

 its products than on coal tar; consequently much less is publicly 

 known about this material. 



The similarity of water-gas-tar creosote and coal-tar creosote makes 

 it seem very probable that in general the hydrocarbons found in the 

 highly aromatic water-gas tars are the same as those found in coal 

 tars. Benzol, toluol, xylol, naphthalene, phenanthrene, . and methyl 

 anthracene have been identified. The most notable difference be- 

 tween coal-tar creosotes and water-gas-tar creosotes is the nearly 

 total absence of tar acids and tar bases in the latter and their presence 

 in considerable amounts in the former. On account of the lack of 

 these materials the odor of water-gas-tar creosotes is more oily than 

 the odor of coal-tar creosotes. 



CHEMICAL PROPERTIES OF WATER-GAS-TAR CREOSOTES. 



The chemical properties of water-gas-tar creosotes are in general 

 the same as those of coal-tar creosotes from which the tar acids and 

 tar bases have been removed. Only a very small proportion is re- 

 acted upon by caustic soda or dilute mineral acids. Concentrated 

 sulphuric acid forms many sulphonic acids which are identical with 

 the sulphonic acids produced from coal-tar creosotes. 



PHYSICAL PROPERTIES OF WATER-GAS-TAR CREOSOTES. 



Because of the great similarity between water-gas-tar creosotes 

 and coal-tar creosotes, the physical properties of one material would 

 in general be the same as those of the other. The same solvents can 

 be used for both. In general, the color of water-gas-tar creosote is 

 somewhat more greenish, although this does not always hold true. 

 The specific gravity of water-gas-tar creosotes is somewhat lower 

 than the specific gravity of coal-tar creosote, varying between 1 and 

 1.07 at room temperature. 



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