Chemistry and Physics. 319 



3. On Normal and Iso-pentane from American Petroleum. — 

 By means of a dephlegmator devised by them, Young and Thomas 

 were able in 1895 to isolate normal hexane from petroleum ether 

 in a nearly pure state. By using a very short water condenser 

 at the top of this dephlegmator, and by combining with it a reg- 

 ulated temperature still-head, the authors have now succeeded in 

 separating normal pentane from iso-pentane. The material used 

 was a complex mixture of butanes, pentanes, and hexanes with 

 some benzene and a little hexanaphthene. Three fractionings suf- 

 ficed to eliminate the butanes, hexanes, benzene and hexanaph- 

 thene for the most part. Then the residues, of about 1030 

 grams, were shaken first with concentrated sulphuric acid, then 

 with a mixture of strong nitric and sulphuric acids ; being finally 

 treated with caustic potash and dried with phosphoric oxide. 

 The details of the eleventh fractionation are given in a table in 

 which the lowest fractions are mainly iso-pentane and the highest 

 normal pentane ; the intermediate ones being mixtures of these. 

 The fall in temperature of the vapor during its passage through 

 the still-head is greatest for the middle fractions and least for the 

 highest and purest fractions. After 13 fractionings the middle 

 fractions had become very small and the two pentanes were sepa- 

 rately fractionated, the normal pentane 8 times and the iso-pen- 

 tane 11 times. In this way 175 grams of pure normal pentane 

 and 101 grams of iso-pentane were obtained. The former boiled 

 constantly at 36*1° under a pressure of 754*5 mm (or 36*3° at 760 mm ) 

 and the latter at 27*95° at 760 mm . The constants of the iso-pen- 

 tane thus obtained were compared with those of the synthetically 

 prepared substance and showed a close agreement. 



The properties of the normal pentane thus obtained are given 

 in a separate paper by Young. The boiling point remained abso- 

 lutely constant at 36*3° at 760 tnm . The specific gravity, deter- 

 mined in the Perkins form of Sprengel tube, was 0-64536 — 0*64541 

 at 0° and 0633 13 at 12*91°. The volumes at different tempera- 

 tures agree closely with those of Thorpe and Jones. The criti- 

 cal temperature was found to be 197*2° and the critical pressure 

 25100 mm ; one gram having a volume of 4*303 cc at the critical 

 temperature. From his results the author shows that the densi- 

 ties of liquid and saturated vapor become equal at the critical 

 temperature and hence defines the apparent critical temperature 

 therefore as the temperature at which the densities of liquid and 

 saturated vapor become equal. This temperature was found to 

 be the same whether the temperature had been previously raised 

 or lowered and whether the volume was constant or variable. — 

 J. Chem. Soc, lxxi, 440, 446, April, 1897. G. f. b. 



4. On the Heat of Combustion. — The formula of Dulong 

 which gives the heat of combustion of solid and liquid fuels as a 

 function of their composition is as follows : 



cp — 81c + 345 



H) 



