METALS. 



99 



ductivity appears to be unknown, which is also true of the purity of the 

 specimen examined. 



The metals, with the exception of aluminum, were obtained from 

 Kahlbaum and from Heraeus. Pure cobalt is, of course, practically 

 unobtainable, and the specimen examined probably contained from 1.5 

 to 2 per cent nickel. 



Hagen and Rubens (loc. cit.) have computed the absorption of the 

 metals from the electrical conductivity by means of the formula 



100 R= 3 ~ 5 where R is the reflecting power, c is the reciprocal of 



the resistance of a conductor I m. long and I sq. mm. area, in ohms, 

 and I = wave-lengths in /* = o.ooi mm. They found a slight varia- 

 tion in the observed and computed values of 100 R, the maximum 

 being about 0.5 per cent at 12 p. It must be said, however, that if 

 they had selected the wave-length i 10.49 P, where in many cases 

 the value of R is frequently the same as for 12/1, the discrepancy 

 would be larger, and of the same order as that observed in the present 

 results. In the present work no attempt was made to attain the accu- 

 racy of these two investigators, for the reason that the nature of the 

 material would not permit it. The difference in the observed and com- 

 puted values of 100 R is given in the following table, using the values 

 of the electrical conductivity as found by Jager and Diesselhorst. 1 



TABLE II. 



The agreement in the observed and computed values (excepting tin) 

 is as close as one can expect from the nature of the metals examined. 



REFLECTING POWER OF SOLUTIONS. 



It is well known that in the visible and in the ultra-violet the position 

 of the maximum of absorption of a solid is generally not affected when 



1 Jager and Diesselhorst, quoted in Landolt and Bornstein, Tabellen. 



