COAL-TAR AND WATER-GAS TAR CREOSOTES. 



45 



same fractions. The dots represent water-gas-tar creosotes, and the 

 circles represent coal-tar creosotes. Here it is seen that, although in 

 a general way the water-gas-tar creosotes are somewhat lower than 

 the coal-tar creosotes, yet they intermingle to a degree so great that 

 no differentiation could be obtained by this method. Furthermore, 

 the figure indicates very strongly that the sulphonation residues and 

 the index of refraction values are proportional to each other in some 

 inverse ratio. In other words, index of refraction values could be 

 obtained in a very general way by the sulphonation test. 



Figures 27a, 27b, 27c, and 27d show the results of plotting specific 

 gravity against index of refraction for the various fractions. Here 

 the specific gravities of water-gas- 

 tar creosotes are lower for the same 

 index of refraction values than are 

 those of the coal-tar creosotes, and 

 there seems to be a somewhat defi- 

 nite line of demarcation between 

 the two. However, the range of 

 coal-tar creosotes and the range of 

 water-gas-tar creosotes are each so 

 much wider than the difference be- 

 tween the two ranges that mixtures 

 of a high-grade water-gas-tar creo- 

 sote and a high-grade coal-tar 

 creosote would probably be classed 

 as a coal-tar product, and mixtures 

 of a low-grade coal-tar creosote and 

 a low-grade water-gas-tar oil would 

 probably be classed as a water-gas- 

 tar product. In other words, al- 

 though it is possible by this method to obtain figures showing a 

 difference between pure water-gas-tar products and pure coal-tar 

 products, it would be extremely difficult to say with any degree of 

 authority that a given sample of oil was or was not a mixture of 

 water-gas-tar and coal-tar products. 



This method of plotting specific gravity against index of refraction 

 for the individual fractions is the only one that has been found at the 

 Forest Products Laboratory for differentiating water-gas-tar creosotes 

 of low-sulphonation residues from coal-tar creosotes which can be 

 recorded numerically. In addition to this, the odor of water-gas-tar 

 products is characteristic. The recording of this odor, however, 

 involves a large personal equation and is of value to the expert only. 

 It is also well known that water-gas-tar products contain no tar 

 acids or, at any rate, only a small amount, and practically no tar 



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PERCENT OF SULPHONATION RESIDUE 



Fig. 26.— The relation between the index of refrac- 

 tion values and the amount of sulphonation residues 

 of fractions of authentic creosotes. 



Circles — Coal-tar creosotes. 



Dots— Water-gas tar creosotes. 



