COAL-TAE AND WATER-GAS TAR CREOSOTES. 



81 



increase m gravity appears to be a straight-line relation depending 

 upon the gravity of the oil, the gravity of the tar, and the proportion 

 of each in the mixture. The gravity of any solution may, therefore, 

 he calculated from the gravity of its two €omponents by the follow- 

 ing formula: Specific gravity solution = per cent tar (specific gravity 

 tar) -f per cent creosote (specific gravity creosote) . Figure 38 shows 

 the change in specific gravity of a creosote with the addition of various 

 amounts of a tar. The curve is drawn from the equation : the points 

 are from experimental data. 



COEFFICIENT OF EXPANSION. 



No data are available on the coefiicient of expansion of tar solu- 

 tions; but it would seem probable that the factor could be calculated 

 from the known values for 

 the change in the specific 

 gravities of creosote and tar, 

 respectively, on the assump- 

 tion that the factor will be 

 in direct proportion to the 

 percentages of each of the 

 two components in the mix- 

 ture. J. M. Weiss (15) has 

 published the results of in- 

 vestigations on the coeffi- 

 cient of expansion of tars 

 from various sources, and 

 shows that the average co- 

 efficient of expansion from 

 60° F. to 140° F. varies from 

 0.00027 to 0.000375 per de- 

 gree Fahrenheit, the former 



being for a tar having a specific gravity of 1.296 and the latter for a 

 tar having a specific gravity of 1.073. If these data be recalculated 

 to a change in specific gravity per degree Fahrenheit, the factor will 

 vary between 0.00035 and 0.00040, with an average of 0.000375. If, 

 then, this factor be taken for the change in specific gravity of tar, 

 and the factor 0.00043 be taken for the change in the specific gravity 

 of creosote oil, the factors shown in Table 31 will be the change in 

 specific gravities of tar mixtures, and should give results close 

 enough to the true value for all commercial purposes. 

 75535°— 22 6 



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Fig. 38.— The change in specific gra^'ity of tar solution. 



