ABSTEACTS: PHYSICS 223 



the stains by aqua regia before making further deposits. This heat- 

 ing process transforms the platinum black to platinum gray and the 

 loss in weight apparently suffered by the cups may be anything from 

 0.1 mg. to 5.0 mg., depending on the amount of material adsorbed by 

 the platinum black. The presence of either platinum black or plati- 

 num grey in the cup renders the cup unfit for use in measuring the 

 electric current since they exercise a catalytic action on the hydrogen 

 ions present in the solution and therefore the amount of silver deposited 

 is too small to represent all of the electricity which actually passed 

 through the voltameters. 



Taking these sources of error into consideration we have made de- 

 terminations of the losses in weight of deposits from pure electrolyte 

 and find, as the mean of 25 determinations, that it amounts to 0.0040 

 per cent. 



The Bureau of Standards published some time ago an absolute value 3 

 for the electrochemical equivalent of silver which was obtained by the 

 silver voltameters containing especially pure electrolyte and an abso- 

 lute current balance of the Rayleigh type. The value found was 1.11805 

 mg. per coulomb which may be now corrected by subtracting 0.0040 

 per cent. It thus appears that the value 1.11800 mg. per coulomb 

 which was adopted by the International Electrical Conference in 1908 

 is in reality within one part in one hundred thousand of the best value 

 which we can now assign to this constant. On this basis, and using 

 the present value for the atomic weight of silver (107.88), we find the 

 farady to be 96,494 coulombs. G. W. V. 



PHYSICS.- — A study of instruments for measuring radiant energy in 

 absolute value: an absolute ihermo-pile. W. W. Coblentz and W. 

 B. Emerson. Bureau of Standards Scientific Paper No. 261. 

 Pp. 49. 1916. The 'present status of the determination of the con- 

 stant of total radiation of a black body-. W. W. Coblentz. Bureau 

 of Standards Scientific Paper No. 262. Pp. 30. 1916. 



The first paper gives the results of an investigation of an instru- 

 ment for measuring radiant energy in absolute value. The instrument 

 consisted of a thin blackened strip of metal with a thermopile back of 

 it. The strip of metal functions (1) as a receiver for absorbing radiant 

 energy, (2) as a source of radiation (by heating it electrically) which can 

 be evaluated in absolute measure and (3) as a standard source of radia- 



3 Bulletin Bureau of Standards 10: 477. 1914. 



