COAL-TAR AND WATER-GAS TAR CREOSOTES. 
91 
Woror infer 
~^~ ' "Cap of fitter paper 
*< Or Alundum W<-,ro 
Wire. Support 
Water Out/et 
fiook ro support wire 
Condanser 
or A/undum Wore 
n/rar Cup 
£-No.S7SS*S PqpWS 
Method. — Weigh. 10 grams of dry creosote in 100 cc . beaker. Add about 50 cc . of pure 
benzol and transfer at once to the filter cup. The filter cup or thimble is previously 
weighed, and the paper cup shall always be kept in a weighing bottle until ready for 
use. Wash out the beaker with benzol, passing all washings through the filter cup 
and place the latter at once in the extraction apparatus. 
Extractor shall contain a suitable quantity of pure benzol. Sufficient heat to boil 
the solvent shall be provided by means of an electric heater or a steam bath. 
Continue the extraction until the descending solvent is practically colorless and 
remove the filter cup and dry in steam oven until all solvent is driven off; cool in 
desiccator and weigh. The balance used for this purpose should be accurate to 
0.5 mg. 
DAVIS SPOT TEST. 
T. H. Davis (46), in 1909, pro- 
posed a test, which he called the 
spot test, for the preliminary 
testing of creosote oil for free 
carbon. This test has been used 
for a long time by distillers, and 
consists in placing 6 drops of the 
oil on blotting paper and noting 
the character of the spots which 
remain. If free carbon is present 
it will manifest itself by a ring 
of free carbon the same size as 
the spot, but the oil will spread 
out into a ring 1 to 2 or 2^ inches 
in diameter. This test is ex- 
ceedingly delicate and shows the 
presence of very minute quan- 
tities of carbon; for this reason 
it is of small value for deter- 
mining the amount of free carbon 
in creosotes. It will, however, 
show whether the regular free-carbon determinations should be made, 
and is of value as a preliminary test for this purpose. The test itself 
has not been given by creosote chemists the attention it deserves. 
H. Cloukey (47) shows that the test may be applied for a preliminary 
examination and will give a good indication to the analyst of what 
he may expect to find in the creosote under examination. When 
the color, character, and size of the spot are taken into consideration 
remarkable approximations may be made, provided a large number 
of authentic spots are available. Pure coal-tar creosote, pure water- 
gas-tar creosote, coal tar, water-gas tar, wood tar, wood-tar creosote, 
and petroleum oils all give spots that are characteristic of themselves 
and different from the others. Mixtures of creosote with tars also 
give characteristic spots. 
Fig. 43. 
-Type of extractor recommended for "free 
carbon" test. 
