100 G. HARKER. 



below 110*6°, No. 2 from 110*6 to 140°, No. 3 above 140°. 

 A distillation test is then applied to Nos. 1 and 2, and a 

 table for each is provided whereby the percentage of toluene 

 is estimated. 



From the divergence of the methods described, and in 

 view of the more or less limited range covered by any of 

 the distillation tables correlating volumes of fractions col- 

 lected up to and between certain temperatures with benzene 

 and toluene content, it was not considered advisable to 

 proceed with the analysis of any samples of coal tar oil 

 before making a series of blank experiments in which pure 

 benzene and toluene in known quantity could be used. This 

 was done in the first instance, to determine the reliability 

 of the distillation test under observed conditions. As it 

 was found that consistent results could be obtained from 

 two or more distillations of any given mixture of benzene, 

 toluene and xylene, provided the conditions were kept con- 

 stant, the blank test method, as will be explained later,, 

 was used for the final determination of the benzene and 

 toluene content of the coal tar oil samples, it being con- 

 sidered that this method was as quick and reliable as any 

 that could be used. Fortunately for the purpose of the 

 blank tests KahlbaUm's pure chemicals were available. 

 The benzene and toluene boiled constantly at 80*2° O. and 

 110*5° O. respectively, and a sample of Kahlbaum's xylene 

 (containing evidently the isomers of xylene) which was also 

 used, distilled over between 134° and 139°, but mostly 

 between 136° and 138°. 



A Young and Thomas still-head of five sections was 

 employed to assist fractionation, as giving greater definition 

 than an ordinary distillation flask, and the rate of distilla- 

 tion was kept at one drop per second. The same still-head 

 and rate of distillation were maintained throughout the 

 analytical work on all samples and blank tests. 



