CAPACITY FOR HEAT OF METALS AT DIFFERENT TEMPERATURES. 137 



8l ri"V V. 



The potential difference at the ends of the heating coil was always balanced against 

 an integral number of standard Weston cells in series. A batch of 25 cells was 

 constructed for use in this investigation, according to the method descril>ed by 

 G. A. HII.KTT ("The Construction of Standard Cells, &c.," 'Physical Review,' 

 Vol. XXXII., 1911). 



The glass work was of the usual H form, the platinum leads not being sealed 

 through the glass. The two limits extended about 15 cm. above the cross tube, and 

 were closed by corks ; through these corks passed the electrodes sheathed by capillary 

 tubing, the fine platinum wires projecting 5 mm. beyond the sealed ends. 



This mode of construction admits of the cells being directly immersed in water, 

 with the limbs projecting about 7 cm. above the surface. 



The water tank containing them was of considerable capacity and well lagged, the 

 temperature rarely varying by one-fifth of a degree Centigrade per day. 



The leads from the cells passed to a switchboard across well insulated supports. 



The cells were frequently compared by means of a Thomson- Varley potentiometer 

 with two standard Westou cells constructed by Mr. F. E. SMITH of the National 

 Physical Laboratory. (We take this opportunity of thanking Mr. F. E. SMITH for 

 presenting us with these cells.) Table I. gives the values of the cells in terms of the 

 N.P.L. standard. All our results are expressed in terms of these standards. 



From an examination of the comparisons at various times during the course of 

 fifteen months, we can find no change greater than that which might be attributed 

 to the experimental errors. 



TABLE I. 



Temperature 17 C. 

 The National Physical Laboratory Standards are denoted by symbols BC 1, BC 2. 



1 The tables used in the reduction of the ohiervations express the E.M.F. of our cells in terms uf the 

 standards correct to 1 part in 20,000. 



VOL. OOXIII. A. T 



