Chemistry and Physics. 483 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On Electrolytic Dissociation and Osmotic Pressure. — It has 

 been already shown by Tratjbe that if N gram-molecules be 

 present in one liter of the co-volume* of any liquid, the pressure 

 will equal 22 38 N atmospheres. If now we suppose water and a 

 sugar-solution separated by a semi-permeable membrane, the 

 water containing N molecules in each liter of its co-volume and 

 the sugar solution N molecules of water to v molecules of sugar, 

 the author considers that the v sugar molecules may enter into 

 unstable union with a molecules of water, and the number of 

 water molecules entering the membrane from opposite sides will 

 be in the ratio N : (N — av) ; thus producing the observed contrac- 

 tion in volume. Consequently the pressure on the side of the 

 solution will be less than on the side of the water by 22*38 av 

 atmospheres. If a be unity, the pressure observed is in accord 

 with the theory of Van't Hoff ; so that it follows that the decrease 

 of pressure on the side of the solution, due to the combination of 

 the water with the dissolved substance, is the osmotic pressure. 

 It has been shown by Poyntingf that if this origin be assigned to 

 the osmotic pressure, we can at once account for most of the 

 observed relations. Some exceptions have been noted in the case 

 of electrolytes. But these may be explained by variations in the 

 value of a ; so that it is not necessary to assume electrolytic dis- 

 sociation in these cases. — Ann. Phys. Chem. y II, lxii, 490-506, 

 October, 1897. G. f. b. 



2. On a New Substance for increasing the Angle of Potation. 

 — In his investigations on the malic acids Walden has made 

 much use of their optical rotation. And since this rotation is 

 slight, he has sought to increase its amount without changing its 

 direction. The effect of oxygen salts of boron in this particular, 

 had been observed by Biot and Pasteur ; and that of the oxy-salts 

 of arsenic, antimony, molybdenum and tungsten, by G-ernez. But 

 their action was feeble. In the salts of uranyl, however, the 

 author found substances fulfilling all requirements. Either 

 uranyl acetate or nitrate may be used, but the latter is preferable 

 because of its greater solubility. To the solution to be examined, 

 potassium hydrate solution is first added and then the solution of 

 uranyl nitrate, the clear yellow solution thence resulting being 

 examined in the polariscope in sodium light. The potassium 

 hydrate solution contained 10*8 grams and the uranyl nitrate solu- 

 tion 40 grams to the 100 cc . Using /-malic acid solution alone (13 

 grains in 100 cc ) the rotation in a tube 2 decimeters long was only 

 — 0*01° and the specific rotatory power — 0*77°. When to l cc of 

 the malic acid solution, 2 CC of the potassium hydrate solution was 



* See this Journal, IV, iii, 479. June, 1897. 

 f Phil. Mag., V, xlii, 289, 1896. 



A.M. Jour. Sci. — Fourth Series, Vol. V, No. 30.— June, 189S. 

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