Intelligence and Miscellaneous Articles. 291 



the Geissler tube. A short wire is then slid along the parallel 

 wires connecting them across like a bridge between two parallel 

 wires on a sonometer. At certain definite points the Greissler 

 tube glows, and the wave-lengths of the electrical oscillations can 

 thus be measured. Lecher finds that the velocity of electricity in 

 metallic wires is the same as that of light. He points out a 

 slight inaccuracy in Hertz's work. — American Journal of Science, 

 Feb. 1891, p. 156 ; Ann. der Physih, Nov. 12, 1890, pp. 850-870. 



ON THE HEAT OF EVAPORATION OF LIQUEFIED GASES. 

 BY E. MATHIAS. 



The author uses a calori metrical method of constant temperature ; 

 the heat withdrawn from the water-calorimeter by the evaporation 

 of the gas is each moment restored by bringing strong sulphuric 

 acid into the water of the calorimeter. It was therefore necessary 

 to determine the heat of dilutiou of the sulphuric acid required for 

 the measurements. With this view small glass flasks containing 

 sulphuric acid were broken under water. A copper cylinder 3 cm. 

 in diameter and 9 cm. in height was used as evaporator ; this is 

 connected at the top to a serpentine tube which was coiled several 

 times round the cylinder, and on its emergence from the Berthelot's 

 calorimeter it was insulated thermally from the rest of the tube by 

 a connector of celluloid. 



In the latter were two taps, a mauometer, and finally a flask of 

 special construction containing glycerine, in order accurately to con- 

 trol and regulate the rapidity of the evaporation. The introduction 

 of the sulphuric acid was effected by an apparatus of the nature of a 

 wash-bottle. Those parts of the metal which came in contact with 

 the acid were thickly gilded The author worked with sulphurous 

 acid, nitrous oxide, and especially with carbonic acid with a range 

 of temperature of 0° to 31°. At the high temperatures the whole 

 room was heated to the corresponding temperature. 



In this way even the worst determinations did not differ by more 

 than 2 per cent, from the mean. The results of experiments with 

 S0 2 and C0 2 agree very well with those deduced from Clapeyron's 

 equations. The differences with nitrous oxide arise from the gas 

 being impure from the presence of nitrogen. With all three bodies 

 the heat of evaporation decreases with increase of temperature 

 within the interval in question. For sulphurous acid this is the 

 linear equation, 



A = 91-87-0-384*. 



For carbonic acid and nitrous oxide, whose critical temperatures 

 are between 31° and 36°-4, the decrease is very steep and can be 

 well expressed by a function of the temperature of the second 

 degree. For carbonic acid, 



X 2 = 117-303(31— — 0-466(31 — *) a . 



