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 PEBCEHT 0F SULPH0NAT,bN RES,DUE 
a low-grade Water-gaS-tar oil Would Fl( f • 2 6.-The relation between tlie index of refrac- 
° tion values and the amount of sulphonation residues 
probably be classed as a water-gas- of fractions of authentic creosotes. 
1 J & Circles— Coal-tar creosotes. 
tar product. In Other WOrds, al- Dots— Water-gas tar creosotes. 
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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