390 GOODWIN ELECTROLYTIC CALCIUM. [Nov. 4, 



specific gravity was found to be 1.5446 at 29.2° C, which is com- 

 pared with some other metals in the following table: 



Li 59 Sb 6.76 Ag 10.505 



K 87 Zn 7.00 Pb 11.38 



Na 97 Sn 7.35 Hg 13.58 



Rb 1.52 Fe 793 Au 19.258 



Ca 1.54 Co 8.55 Pt 21.5 



Mg .... 1.74 Cu 8.89 Ir 22.4 



Al 2.68 Bi 9.82 Os 22.5 



Conductivity. 



On the milling machine a piece of calcium about 10 cm. long 

 was accurately finished on the sides and measured 1.43 X i-02 cm. 

 It was imbedded in a block of wood with a mercury cup at each 

 end and connected through a 15- ampere Weston ammeter, variable 

 resistance and switch with storage batteries. Sharp brass potential 

 points near the ends led to a large, very sensitive, horizontal 

 D'Arsonval galvanometer whose deflections were read by a tele- 

 scope and scale. The value of the galvanometer deflections in volts 

 was obtained by using a standard low resistance in place of the 

 unknown piece of calcium. The average of several readings gave 

 the resistance between points 7.2 cm. apart 19.4 microhms at 30° C, 

 and 26.7 microhms at 123° C. in a bath of hot parafifin. 



Solving the equations 



1^30 = 1^0 (I + 3o«) = 194 

 ^123 = ^0 (I + 123a) 



we get the resistance at 0° C. 



Rq =: 16.94 microhms 

 and the temperature coefficient 



a = .00457. 



Hence the specific resistance at 0° C. 



16.94 X I.02 X 1-43 

 = —— = 3.43 microhms per cm. cube. 



At the mercury cups calcium slowly formed a voluminous 

 amalgam. 



In the table below these values for calcium are placed in Sir 

 Roberts-Austen's relative electrical conductivity table and show 



