298 Scientific Intelligence. 



change of specific volume, is r= T [dp/dt(s r — s)— y\. The experi- 

 mental work was done mostly upon starch. This substance, when 

 air dried, was found to contain about 16*33 per cent of water. 

 By means of an ice calorimeter, the heat which is produced by 

 soaking in water starches having originally different amounts of 

 moisture was determined, the results being tabulated and plotted 

 as a curve. The contraction in volume as a function of the per- 

 centage of water, was also noted and plotted ; the curve being 

 similar to the heat curve. From the values of the heat change 

 and the volume change for the dry and moist starch, dp / dt and 

 y in the equation given above are obtained ; thus giving the 

 numerical equation r = 273 (s f — s) 1*75 — 0-00507. Next, the 

 author deduces a relation between the heat of swelling (and hence 

 the volume change) and the water content and thus derives the 

 equation log (s'~ s) w = 0*8 — 2 — 00423 w. Consequently when 

 w= 31*63, y = 0. An expression given by Kirchhoff for the 

 vapor pressure of sulphuric acid solutions is used to calculate 

 that of the starch; the result being 4*5594 for a content of 31*63 

 per cent of water. The author deduces from this calculated 

 value of the vapor pressure, the number 4370 as the molecular 

 mass of starch; corresponding to the formula C 162 H 270 O 136 . More- 

 over, he finds the expansion-coefficient to be a linear lunction of 

 the content of water. And he calculates the attractive force 

 between dry starch and moisture as 2073 kilograms per square 

 centimeter. — Zeitschr. Phys. Chem., xxiv, 193-218, October 1897. 



G. F. B. 



3. On the Evolution of Oxygen during Reduction. — When 

 rubidium dioxide is reduced by hydrogen, oxygen is evolved ; a 

 fact which Erdmann attempted to explain by supposing the 

 intermediate formation of hydrogen peroxide. Frenzel, Fritz, 

 and Victor Meyer have now made experiments to test this 

 explanation, in some of which the formation of hydrogen per- 

 oxide was not possible. Thus on heating potassium peroxide to 

 the softening point of glass (the vessel being of silver) in a cur- 

 rent of air, no oxygen is evolved. But when heated in carbon 

 monoxide, carbon dioxide, or hydrogen, to the boiling point of 

 sulphur, a considerable amount of oxygen is set free. Now in 

 the case of carbon monoxide, as well as in that of the dioxide, the 

 formation of hydrogen peroxide as an intermediate product is 

 impossible. So that the three reactions appear to be analogous : 



K,O 4 +0O = K,CO ( + O 1 



(K,0 4 ) i + (CO.), = (K 1 CO i ), + (0,) 1 

 K 2 0, + H 8 =(KOH) a + O g 



Again, silver oxide decomposes when heated to 250° in a current 

 of air; but in hydrogen it yields free oxygen even when heated 

 only to the boiling point of water. Indeed, it evolves oxygen in 

 carbon monoxide even at the ordinary temperature ; the fact 

 being that a portion of the oxide in reduction evolves sufficient 

 heat to raise the temperature of the rest above the decomposing 



