98 
BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 
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 different 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 fractions 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 
Average-gravity creosote . . 
Low-gravity creosote 
(Very exceptional cases.) 
1.047 
1.036 
1.025 
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 oo 8T - 
38 
15' 
Fraction 
315° to 
355° C 
S Poo gn 
38 
15' 
Composition of mixture. 
Fraction 
235° to 
315° C. 
S Poo^- 
38 
15' 
Fraction 
315° to 
No. 
Creosote. 
Coal tar. 
Water- 
gas tar. 
No. 
Creosote. 
Coal tar. 
Water- 
gas tar. 
355° C. 
Sp oo gr - 
38 
15* 
1 
Per cent. 
65 
90 
65 
65 
60 
55 
Per cent. 
25 
Per cent. 
10 
10 
15 
15 
15 
22.5 
1 1. 028 
1.033 
1.031 
1.033 
i 1. 028 
i 1. 025 
1.102 
1 1. 088 
1 1.090 
» 1. 085 
1.101 
7 
8 
9 
10 
11 
Per cent. 
65 
55 
65 
65 
65 
Per cent. 
Per cent. 
35 
45 
15 
25 
35 
1.042 
1.038 
1.041 
1.038 
1.038 
1.120 
? 
1.112 
3 
4 
20 
20 
25 
22.5 
20 
10 
1.112 
1.106 
1.104 
6 
1.100 
1 Indicates failure to pass specifications. 
