494 SCIENTIFIC RECORD FOR 1884. 



is evolved, and a diminution of bulk takes place. If any excess of etber 

 present be poured off", and tlie lower clear liquid heated in a sealed tube, 

 it becomes turbid, owiug to the separation of the ether. This is accom- 

 panied by an increase in bulk aud absorption of heat. 



Alcohol and carbon disulphide foini a typical case of the second class 

 of mixtures. These liquids mix with each other, in all i)roportions above 

 0° C, with increase of bulk and ahsorption of heat. Upon cooling the 

 mixture to about —17° C. the liqnids separate. In these cases the 

 action is regarded as a chemical one. {Chvm. Xeics, l, 233.) 



Ow a Relation between the Molecn'ar Weights of Liqnids and their Veloc- 

 ities of Evaporation, by C. Schall. — On distilling successively in the same 

 apparatus given volumes of benzene and of water, the author found that, 

 even when the boiling was maintained as nearly uniform as possible, 

 very different weights of these two substances passed over in the same 

 time. Even in a rough experiment the quantity of benzene in the re- 

 ceiver was double that of the water. With a view to give the experi- 

 ment greater exactness, the time of evaporation of equal volumes of these 

 liquids was carefully determined. Knowing, then, the density of the 

 liquids at the boiling point, their weights could be calculated, and hence 

 the exact time of evai)oration of equal weights. 



On comparison the values thus obtained appeared to be very nearly in 

 the inverse ratio of the mi)lecular weights of the liquids en)j)loyed. Thus, 

 benzene, with a boiling point of 70.2° and a density of 0.81 36, evaporated 

 in 12.7, 12.U5, and 12.3 minutes ; while the same volume of chloroform, 

 boiling point 61.5° and density 1.4048, evaporated in 14.3, 14.5, and 14.3 

 minutes; or, reduced to equal weights, in 8.25, 8.4, and 8.28 minutes. 



Since m : m' = t' : t, the .first value gives for the molecular weight of 

 chloroform 119.64, the second 120.25, and the third 119.88, the true value 

 being 119.5. Benzene, when compared with carbon disulphide, boiling 

 point 45.3'^ and density 1.2212, evaporated in 12.3 minutes, while the 

 same volume of OS2 required 19 minutes ; or, reduced to equal weights, 

 12.66 minutes. This gives, by calculation, a molecular weight of 75.79 

 in place of 76. Water, boiling point 99° and density 0.9596, evaporated 

 in 64 minutes ; or, reduced to equal weights, in 54.26 minutes. This gives 

 a molecular weight of 17.68 instead of 18. Moreover, the ratio of the 

 volumes of two liquids evaporated in equal times is the ratio of their 

 molecular volumes. Thus, the ratio for benzene and chloroform above 

 given is 1.126:1; whence 1.126:1=95.94 (the molecular volume of 

 benzene) : 85.2 (the molecular volume of chloroform). Schiff" obtained 

 84.65. The author has further observed that on comparing Kegnault's 

 values of the heat of vaporization of several liquids, these numbers de- 

 crease as the molecuiar weight increases. From which, of fifteen liquids 

 whose heat-data are known, thirteen fall readily into five groups, in each 

 of which the product of the heat of vaporization by the molecular weight 

 is approximately constant. Thus, water gives 536.67x18=9660.06, 



