August 1, 1902.] 



SCIENCE. 



173 



air is cooled enough to liquefy. The liquid 

 air is collected in double-walled glass ves- 

 sels with a vacuum between the walls. 



In this test the power supplied during 

 an hour was accurately measured, as was 

 also the amount of liquid air obtained. By 

 an expenditure of 25 horse power for one 

 hour 2,919 grams of liquid air were pro- 

 duced. That is, the expenditure of one 

 horse power per hour produces 116 grams 

 of liquid air. The low temperature of the 

 liquid air renders a certain amount of heat 

 energy available. To vaporize one gram 

 of the liquid requires 50 calories, or heat 

 units. To raise the temperature of the gas 

 from the boiling point of liquid air 

 ( — 190° C.) to ordinary atmospheric tem- 

 perature requires 47 calories more. The 

 total amount required per gram is there- 

 fore 97 calories. For 116 grams there 

 would be reciuired 11,310 calories, or if the 

 energy is expressed in mechanical units it 

 amounts to 35,000 foot pounds. 



In other words, the expenditure of one 

 horse power continuously for one hour re- 

 sults in the production of just enough 

 liquid air, which if it were utilized in its 

 turn as a source of power in a perfect ma- 

 chine, the greatest amount of power obtain- 

 able would be one horse power for one 

 minute. The most efficient method of ob- 

 taining liquid air as yet discovered, would 

 increase this last period of time to five 

 minutes! 



The efficiency of the plant discussed in 

 this paper was thus very low, being not 

 quite two per cent. 



The Theory of the Electrolytic Rectifier i 

 K. E. GuTHE, University of Michigan. 

 The paper described the method of inves- 

 tigation and was illustrated by means of 

 curves showing the relation between the 

 current and the reaction, or polarization, 

 or condensation voltage, with different 

 metals and salt solutions. 



Rayleigh's Alternate Current Phasemeter: 

 E. S. JoHONNOTT, Rose Polytechnic Insti- 

 tute. 



In the Philosophical Magazine for May, 

 1897, Lord Rayleigh has described a 'soft- 

 iron galvanometer' which is quite suitable 

 for measuring all quantities such as are 

 ordinarily measured with ammeters, volt- 

 meters and wattmeters. It consists of a 

 soft-iron needle suspended between two 

 parallel coils at an angle of 45° to their 

 common axis. Besides furnishing a simple 

 means for determining the phase relation 

 in circuits, the instrument may be used as 

 a wattmeter. Breslaurer has recently 

 shown that it has advantages over the elec- 

 trodynamometer used as a wattmeter on 

 circuits having low power-factors. 



Some experiments were undertaken with 

 the instrument to determine the iron losses 

 in choking coils where the power- factor was 

 varied over a wide range by increasing the 

 air-gap in the magnetic circuit. 



Ordinarily the connections are similar to 

 those for the wattmeter, the E.M.P. coil 

 being connected across the terminals of 

 the circuit and the other, the current coil, 

 in series with the same. Another manner 

 of using the instrument was found in prac- 

 tice to be much more simple and to give 

 more consistent results. The connections 

 for this method were the same as for 

 Blakesley's split dynamometer. An explor- 

 ing coil, exactly similar to the magnetizing 

 coil, was wound on the magnetic circuit and 

 connected in series with the E.M.F. coil of 

 the phasemeter. 



The instrument is as easily made as any 

 simple form of galvanometer. The laws 

 which connect the readings with the 

 electrical quantities are perfectly similar to 

 those of other alternate current instru- 

 ments. 



Many laboratory exercises, such as the 

 determination of coefficients of self indue- 



