]^apoi(}'-Dens}fies of some Cai'hon Compoiuuis. 495 



dephlogmator. The se})arate tractions were heated with 

 tumincr nitric acid tor several days, and after treatino; with 

 ]iotash. and drying, they were distilled. The comparison of 

 the constants is as follows : — 



Normal hexane from 



Petroleum. Propyl iodide. 



Boiling-point 68-95^ 68-95° 



( 0-67698 



Density at 0° 4^ (four fractions J 067699 ^ ^-^q^ 



afteAvards mixed together) . . 1 0-67697 ^ ^^^^^ 



( 0-67702 



Critical temperature 284-8° 284-8° 



,, pressure 22540 mms. 22510 mms. 



The concordance of these results affords a guarantee of the 

 almost absolute purity of the specimen. 



(2) Sormal octane (Young, iUd. xvi. p. 166). — This 

 sample was made from octyl iodide by Kahlbaum. Its 

 boiling-point at normal pressure after purification by Young- 

 was 125*8°. It was collected in three fractions, which showed 

 the densities A, 0-71850; B, 0-71847; C, 71848. These 

 fractions were mixed. The boiling-points, determined at 

 different times, were 125-8°, 125-85°, and 125-75°. 



(3) Di-isobutyl (Young, Hid. xvi. p. 165). — Made by 

 Young and Miss Fortey b3^ treating isobutyl bromide with 

 sodium in ethereal solution. " No great difficulty was ex- 

 perienced in the preparation of di-isobutyl, and the yield ^^ as 

 fair. As the boiling-point of the paraffin (109 "2°) is con- 

 siderably higher than that of isobutyl bromide (92*3°), it 

 could be separated fairly completely from the unaltered 

 bromide by fractional distillation. The final purification 

 was effected by treatment with a mixtuj-e of nitric and sul- 

 phuric acids, and subsequent fractional distillation through a 

 twelve-column Young and Thomas dephlegmator. Owing 

 to the partial conversion of the isobutyl bromide into the 

 tertiary bromide a small quantity of hexamethyl-ethane is 

 formed ; but this is completely removed during the fractional 

 distillation." The boiling-points of three fractions were 

 109-2°, 109-2°, and 109-25°; the densitv at 0° was 0-71021 : 

 ^chiff found 0-7103. 



The remaining substances were prepared by ourselves. 



(4) Benzene. -A sample of Kahlbaum^s purest thiophene- 

 free benzene was twice subjected to fractionation ; the boiling- 

 point was absolutely constant. 



(5) To^w^^if?.— Sample A was prepared from paratoluidine 

 by diazotization. Its boiling-point was constant. Sample B 

 was synthesized from bromobenzene and methyl iodide ; the 

 constant boiling fraction was crystallized. As the process of 



