COAL-TAR AND WATER-GAS TAR CREOSOTES. 93 



carefully wiped off and the bulb re weighed. This procedure will give about 1 g. 

 of oil. 



Cut a strip of thin asbestos paper about one-fourth inch wide and about 1 inch long, 

 place it around the neck of the bulb, and catch the two free ends close up to the neck 

 with a pair of crucible tongs. The oil should then be distilled off as in making ordi- 

 nary oil distillation, starting with a very low flame and conducting the distillation as 

 fast as can be maintained without spurting. 



When oil ceases to come over, the heat should be increased until the highest tem- 

 perature of the Bunsen flame is attained, the whole bulb being heated red hot until 

 evolution of gas ceases, and any carbon sticking to the outside of the tubular is com- 

 pletely burned off. The bulb should then be cooled in a desiccator and weighed 

 and the percentage of coke residue calculated to water-free oil. 



DISTILLATION TEST. 



This test has been used nearly as long as specifications have been 

 written for creosote. It is without value for the determination of 

 the source of the oil, because coal-tar creosote, water-gas-tar creosote, 

 blast-furnace oil, certain crude petroleums, shale oils, candle oils, 

 acid residues, and certain others have practically the same range of 

 boiling points. The only value of the distillation test alone is to 

 determine whether an oil of known source meets the requirements 

 of the specification so far as boiling points are concerned. The type 

 of distilling vessel has a considerable influence on the percentage of 

 distillate obtained in any fraction from a given creosote. Because 

 of the exceeding complexity of the mixture, no single distillation can 

 secure an absolutely true apportionment of the oil, no matter how 

 refined the apparatus may be. Therefore, to get concordant results 

 from different operators, it is necessary that the standard form of 

 the distilling vessel should be accurately fixed, that the position of 

 the thermometer should always be the same, that the rate of dis- 

 tillation should be uniform, and that thermometers having prac- 

 tically the same dimensions should be used. The types of vessel 

 that have been proposed for this test are the 8-ounce retort, the 

 ordinary distilling flask, the Lunge trap flask, and the Hempel flask. 

 The first three are used for ordinary commercial work and the last 

 for a more refined test. The first three, when used under standard 

 conditions, will give practically the same average results. The choice 

 of one of the three vessels for such an empirical operation as the dis- 

 tillation test rests, therefore, on the ability of the apparatus to 

 duplicate results. The ability to do this depends on the exact repro- 

 duction of the form, shape, and size of the apparatus. As the retorts 

 are blown by hand in the form of a long pear-shaped glass and then 

 bent down in a flame, the shapes and sizes can not be kept uniform. 

 As a result, a so-called 8-ounce retort may hold anywhere from 4 to 

 12 ounces, depending on the carefulness of the assortment. On the 

 other hand, as flasks of glass are now blown in a mold, the shapes 

 and sizes are practically uniform. One would, for this reason, 



