Chemistry and Physics. 429 



glass in air. Even at a red heat, it is unchanged in air; though 

 it takes fire in the blowpipe flame. Thrown into water, the latter 

 is decomposed and its hydrogen unites with that of the hydride, 

 producing calcium hydrate and hydrogen. Its composition is 

 CaH 2 and it acts energetically as a reducing agent. — C. P., 

 cxxvii, 29, July, 1898. g. f. b. 



3. On an Improved method for determining Molecular Mass 

 by the JBoiling Point. — Early in the present year, Landsberger 

 described* an improved apparatus for fixing the molecular mass 

 of a substance by means of the elevation which it produces in 

 the boiling point of a solvent when dissolved in it. In this appa- 

 ratus the solution is kept at its boiling point by the passage 

 through it of the solvent vapor alone, thus avoiding superheating. 

 Walker and Lumsden have now proposed a modification of this 

 method which consists in measuring the volume of the solution 

 after equilibrium has been attained, instead of its weight. The 

 apparatus consists of an inner tube, to contain the solution, about 

 3 cm in diameter and 20 cm long, graduated up to 30 cc from below, 

 and contained within an outer tube 6 cm in diameter and about the 

 same length. Through a stopper in the inner tube passes a ther- 

 mometer and a tube to convey the vapor of the solvent, both 

 going to the bottom. This vapor, generated in a side flask, 

 passes through the solution in the inner tube, thence through a 

 small hole near its top into the outer tube and on to the condenser. 

 To fix the boiling point of the solvent, about 12 cc of it are placed 

 in the inner tube, and its vapor is then conducted through it from 

 the flask until drops fall from the condenser at the rate of one 

 every two seconds or so, when the thermometer is read. The 

 tube is then transferred to an upright cylinder which it just fits 

 and the volume of the solution is read to tenths of l cc . About 

 half of the liquid is now poured off" and from half to one gram of 

 the substance under examination is added to the remainder in the 

 tube. The vapor is then passed through this as before, the ther- 

 mometer is again read and the volume measured. The latter 

 operation may be repeated half a dozen times and the mean taken. 

 The result may be calculated by the formula 



_ r . Constant X mass of substance 



Mol. mass = 



Elevation x volume of solution. 



The constants for the various solvents are obtained simply by 

 dividing the ordinary weight-constants of these liquids by their 

 densities at the boiling point. Since only one weighing is needed 

 much time is saved, six determinations requiring only a half hour. 

 The volume need be read only to 0'1 CC and the thermometer 

 only to fifths of a degree. Alcohol or ether should preferably be 

 used as the solvent, though acetone gives good results when pure. 

 Values obtained with various substances in various solvents are 

 given which show that the accuracy of the method is quite sufli- 



*Ber. Berl. Chem. Ges., xxxi, 458, March, 1898. 



