SECT. i. METALS AND THEIR PROPERTIES. 5 



form the triatomic group ; they are remarkable for their 

 complex spectra. Mckel is usually an ingredient in 

 meteorites; cobalt is employed in pigments and in 

 sympathetic inks ; and the oxide of uranium is used to 

 stain glass, and gives it some very peculiar properties, 

 as will be shown. The precious metals have a feeble 

 affinity for oxygen at any temperature, and their oxides 

 are decomposed by heat alone, and sometimes even by 

 the undulations of light. 



Metals are excellent conductors of heat, but they vary 

 exceedingly in that respect ; both theory and experi- 

 ment prove that the best conductors are invariably the 

 worst radiators. In fact those atoms which transfer the 

 greatest amount of motion to the ethereal medium, 

 that is, which radiate most powerfully, are the least 

 competent to communicate motion to each other, that 

 is, to conduct with facility. Silver and copper are the 

 best conductors of heat, but the worst radiators. These 

 two metals are the best conductors of electricity, but it 

 is influenced by temperature ; for MM. Matthiessen and 

 Yon Bose's experiments have proved that all pure 

 metals in a solid state vary in conducting power to the 

 same extent between zero and 100 Cent., and that the 

 alkaline metals conduct electricity better when heated 

 than when cold. 



All metals are capable of being vaporized, but at very 

 different degrees of temperature. Platinum requires 

 the heat of the oxy-hydrogen blowpipe, which by esti- 

 rnation amounts to 801. Cent. This property makes it 

 valuable for terminal points to the conducting wires 

 of the voltaic battery and magneto-electric induction 

 machine where great heat can be employed without 

 fusing the platinum terminals. Copper is always em- 

 ployed for the conducting wire on account of its superior 

 conductive power. The coil of wire in the magneto- 

 electric machine, which is often miles long, is insulated 



