Chemistry and Physics. 239 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



i. On the Dead Space in Chemical Reactions. — In 1886, Lieb- 

 reich called attention to the fact that in certain parts of a liquid 

 in which a slow chemical reaction is taking place, either no 

 change at all occurs or the change, if it take place, is diminished 

 or retarded. This portion of the liquid in which the reaction is 

 thus modified, he terms the " dead space." In the present paper, 

 he gives the result of experiments made to determine the cause of 

 this phenomenon. In studying it, he finds the most satisfactory 

 reactions to be (1) the separation of chloroform by the action of 

 sodium carbonate upon chloral, and (2) the separation of iodine 

 by the action of sulphurous acid upon iodic acid ; the extent of 

 the reaction being easily distinguished in the first case by the 

 turbidity given by the chloroform and in the second by the color 

 of the iodine. The dead space appears at the free surface of the 

 liquid and is easily visible to the naked eye. In narrow spaces, 

 such as capillary tubes for example, the reaction is either greatly 

 retarded or entirely prevented, as is clearly seen when iodic and 

 sulphurous acids, mixed with starch solution, are placed in such 

 tubes. When the tube is somewhat wider, the reaction takes 

 place only along the axis, a thin thread of blue being apparent 

 there. In the paper forty figures are given to show the character 

 of the dead space in vessels of various sizes and shapes. As to 

 the cause of the phenomenon, the author proves that the dead 

 space at the free surface of the liquid is not due to evaporation. 

 He considers that the physical influence of the walls of the vessel 

 and the surface-tension of the liquid play an essential part in 

 producing the dead space, there being developed by these actions 

 a certain viscosity in the region where it exists, which hinders 

 the reaction. The fact that the extent of the dead space dimin- 

 ishes with rise of temperature, is in favor of this view. — Zeitschr. 

 Physikal. Chem., v, 529 ; J. Ch. JSoc, Iviii, 1207, Nov., 1890. 



G. F. B. 



2. % New Principle of Determining Molecidar Masses. — Accord- 

 ing to van't Holf and Tammann, isosmotic solutions have equal 

 vapor-pressures. So that, regarding the process of solution as 

 equivalent to that of evaporation, the pressures of different solu- 

 tions toward any special solvent, may be' assumed subject to the 

 same law. Consequently, if two isosmotic aqueous solutions be 

 shaken with a given liquid, say carbon disulphide, this liquid 

 will remove from each, equal quantities of water. If however, 

 the osmotic pressure is different for the two aqueous solutions, 

 that solution which has the lower osmotic pressure will lose more 

 water than the other. The osmotic pressure of a solution, how- 

 ever, is a function of the character and quantity of the dissolved 

 salt; and hence the quantity of water given up will also be a 



