102 Mr. W. Crookes. [June 11, 



the variations in the strength of the current, the experiment lasting 

 some hours, affected each metal alike. 



The exposed surface of the various metals used as negative poles 

 was kept uniform by taking them in the form of wires that had all 

 been drawn through the same standard hole in the drawplate, and 

 cutting them by gauge to a uniform length; the actual size used was 

 0-8 mm. in diameter, and 20 mm. long. 



The comparison metal gold had to be used in each experiment ; the- 

 apparatus thus enabled me to compare three different metals each 

 time. The length of time that the current was kept on the revolving 

 commutator in each .experiment was eight hours, making two hours 

 of electrification for each of the four negative electrodes ; the pressure 

 was such as to give a dark space of 6 mm. 



The fusible metals, tin, cadmium, and lead, when put into the appa- 

 ratus in the form of wires, very quickly melted. To avoid this diffi- 

 culty a special form of pole was devised. Some small circular porce- 

 lain basins were made, 9 mm. diameter; through a small hole in 

 the bottom a short length of iron wire, 0'8 mm. in diameter, was 

 passed, projecting downwards about 5 mm. ; the basin was then filled 

 to the brim with the metal to be tested, and was fitted into the appa- 

 ratus exactly in the same way as the wires ; the internal diameter 

 of the basins at the brim was 7 mm., and the negative metal filed flat 

 was thus formed of a circular disc 7 mm. diameter. The standard 

 gold pole being treated in the same way, the numbers obtained for 

 the fusible metals can be compared with gold, and take their place in 

 the table. 



The following table of the comparative volatilities was in this way 

 obtained, taking gold as = 100 : 



Palladium 108-00 



Gold 100-00 



Silver 82-68 



Lead 75'04 



Tin 56-96 



Brass 51'58 



Platinum 44'00 



Copper 40-24 



Cadmium 31'99 



Nickel 10-99 



Iridium 10*49 



Iron 5-50 



In this experiment equal surfaces of each metal were exposed to 

 the current. By dividing the numbers so obtained by the specific 

 gravity of the metal, the following order is found : 



