98 



BULLETIN 1036, U, S. DEPARTMENT OF AGRICITLTURE. 



distillation of creosote are much more likely to eliminate admix- 

 tures than tests performed on the whole sample. Therefore, too 

 much importance can not be attributed to this test. The specific 

 gravity of the fractions, according to the latest specifications, is 

 taken at 38° C. and referred to water at 15° C. In general, the same 

 result would be obtained by determining the specific gravity at 60° C. 

 and referring to water at 60° C. The data on specific gravity and 

 index of refraction given in the part of this bulletin describing the 

 experimental comparison of creosotes were all taken at 60° C, and 

 referred to water at the same temperature. The present specifi- 

 cations require the specific gravity of two large portions 235° to 315° C. 

 and 315° to 355° C; and, whereas the results obtained by these two 

 fractions seem to be very good, a closer control is obtained by the 

 use of more fractions. On account of the fact that tars and creo- 

 sotes having very difi'erent boiling points are sometimes mixed to- 

 gether, the failure of either fraction to fulfill the requirements of the 

 specification should be sufficient cause for the rejection of the mate- 

 rial under that specification. 



The specific-gravity values of three pure coal-tar creosotes are 

 given in Table 34. 



Table 34. — Specific gravities of Jractions of three pure coal-tar creosotes. 



Type of creosote. 



Fraction 

 235° to 

 315° C. 

 Sp. gr. 



38 



15' 



Fraction 

 315° to 

 355° C. 

 Sp. gr. 



38 



15' 



High-gravity creosote ' 1. 047 



Average-gravity creosote 1. 036 



Low-gravity creosote 1.025 



(Very exceptional cases.) 



1.145 

 1.112 

 1.108 



The examples from the report of the Committee on Preservatives 

 of the American Wood Preservers' Association, 1917, given in Table 

 35, show the necessity of requiring both specific gravities to conform 

 to the specification. 



Table 35. — Specific gravities of fractions of mixtures of coa.-tar creosote, coal tar, and 



water-gas tar. 





Composition of mixture. 



Fraction 

 235° to 

 315° C. 

 Sp. gr. 



38 



15' 



Fraction 

 315° lo 

 355° C. 



38 

 15" 





Composition of mixture. 



Fraction 

 235° to 

 315° C. 



38 

 15' 



Fraction 

 315° to 



No. 



Creosote. 



Coal tar. 



Water- 

 gas tar. 



No. 



Creosote. 



Coa) tar. 



Water- 

 gas tar. 



355° r. 



Sp. gr. 

 38 

 15' 



1 



Per cent. 

 65 

 90 

 65 

 65 

 60 

 55 



Per cerht. 

 25 



Per cent. 

 10 

 10 

 15 

 15 

 15 

 22.5 



1 1. 028 



1.033 



1.031 



1.033 



1 1. 028 



1 1. 025 



1.102 



1 1.088 



1 1.090 



< 1. 085 , 



1.101 1 



1.100 



7 

 8 

 9 

 10 

 11 



Per cent. 

 65 

 55 

 65 

 65 

 65 



Per cent. 



Per cent. 

 35 

 45 



1.042 

 1.038 



1.120 



? 





1.112 



3 



4 

 5 



20 

 20 

 25 

 22.5 



20 

 10 



15 1.041 

 25 1. 038 

 35 1.038 



1.112 

 1.106 

 1.104 



6 











1 Indicates failure to pass specifications. 



