Chemistry and Physics. 297 



such a solution will decrease regularly with its concentration and 

 will be inversely proportional to the molecular mass of the dis- 

 solved substance. Hence the molecular mass of any substance 

 may be determined from the rate of evaporation of one of its 

 solutions, as it may from the depression of the freezing point. 

 Kronbeeg has experimented to determine the best conditions 

 required to put this method into operation. To make a determi- 

 nation, weighed quantities of two solutions, one of a substance of 

 known, the other of a substance of unknown molecular mass, in 

 the same solvent, should be exposed, either in the open air or in 

 a vacuum for a given time and then reweighed. The losses in 

 each case, calculated for one hundred parts of the pure solvent, 

 will be inversely proportional to the molecular masses of the dis- 

 solved substances ; and since one of them is known the other is 

 readily calculated. — Monatsb. Chem., xiv, 24 ; J. C/iem. Soc, 

 lxiii, 261, June, 1893. g. f. b. 



4. On the Boiling and the Freezing points of Nitrogen mon- 

 oxide.— "Rails ay and Shields have determined with care the 

 temperature at which liquid nitrogen monoxide boils and the 

 temperature at which it solidifies at ordinary atmospheric pres- 

 sure. For this purpose they employed a hydrogen thermometer, 

 readings of the pressure being taken at constant volume. The 

 error arising from the difference of temperature between the 

 stem and the bulb and that due to the alteration in the volume of 

 the bulb were eliminated by the method used. The plan adopted 

 was to read the position of the mercury in the capillary stem 

 when the bulb was immersed in water at atmospheric tempera- 

 ture ; to raise it to about 100° by covering it with cotton-wool 

 arid exposing it to the steam of boiling water and to read the 

 increase of the pressure of the gas ; and then to immerse it in 

 the boiling nitrogen monoxide and again to read the pressure, 

 which then of course is reduced. Three determinations of the 

 boiling point made in this way gave the values —90-1°, — 89'8° 

 and — 89'5° ; the mean being — 89'8°. The liquid should be kept 

 actively boiling during the pressure reading, in order to prevent 

 superheating. The solid nitrogen monoxide was produced by 

 covering the bulb of the hydrogen thermometer with cotton-wool 

 and dipping it into the liquid. On removing it and blowing air on 

 the surface the liquid froze and the temperature fell, the pressure 

 falling concurrently. The lowest reading of pressure was taken as 

 equivalent to the melting point of the solid. The temperatures 

 thus observed in two experiments were — 102*5° and — 102 # 1°; 

 the mean being —102 "3°, which may be taken as the fusing point 

 of solid nitrogen monoxide. — J. Chem. JSoc, lxiii, 833, June, 

 1893. G. F. B. 



5. On the Tests for Arsenic. — In 1851 Fleitmann showed that 

 •when a mixture containing arsenic and antimony is added to a 

 solution of caustic alkali and heated, arsine is evolved but no 

 stibine. Hager soon after showed that when the arsenic is in the 

 form of arsenic acid no arsine is evolved under these circum- 



