74 



BULLETIiSr 1036, U. S. DEPARTMENT OF AGRICULTURE. 



VOLATILITY. 



The volatility of three water-gas-tar creosotes is shown in figure 

 3 Id. Here the loss by volatihzation is plotted against the percentage 

 distilling at 270° C. These data were obtained from hemlock treated 

 with water-gas-tar creosotes and held under test for 80 days at a 

 temperature of 40° C. The conditions of these tests were the same 

 as those described in connection with figure 31b, for coal-tar creosotes. 

 The same general result is obtained from these creosotes as from 

 coal-tar creosote, namely, that the volatility increases in some direct 

 ratio to the percentage distilling below 270° C. The character of the 



test, whether from open pan or 

 from treated wood, whether of 

 short or long exposure, and the 

 temperature of heating will, of 

 course, affect the volatility in the 

 same general manner as in coal-tar 

 creosote. Different results would 

 probably also be obtained if dif- 

 ferent species of wood were used. 

 A comparison of the two curves, 

 which are comparable as far as 

 treatment, wood, temperature of 

 heating, and length of exposure 

 are concerned, reveals the fact that 

 the volatility of water-gas- tar creo- 

 sote is the same as that of coal- 

 tar creosote having the same per- 

 centage of distillate below 270° C. 

 It follows, therefore, that the dis- 

 cussion of the volatility of coal- 

 tar creosotes will apply equally 

 well to water-gas-tar creosotes. 



VISCOSITY. 



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DEGREES ABSOLUTE 



Fig. 35. — Change in \'iscosity of water-gas-tar 

 creosotes with change in temperature. 1. 

 Very high boiling oil. 2. Similar tea tiigh- 

 boiling creosote. 3. Low-boiling oil. 



The change in viscosity with a 

 rise in temperature for three water- 

 gas-tar creosotes of widely different characteristics is shown iu 

 figure 35. The creosotes are pure distilled products without the 

 addition of any tar. The change in viscosity of water-gas-tar creo- 

 sotes with change in temperature can be calculated in the same 

 manner as that of coal-tar creosotes according to the equation, 

 Y 

 -7HX = K, where V is the absolute viscosity, T the absolute temperature, 



and K and A are constants depending upon the oil. The equations, 



