272 



CHEMISTRY. 



taper had been introduced. So, also, if a piece be held in 

 a current of hydrogen it becomes red-hot, and then sets 

 fire to the gas. This is what takes place in Dobereiner's 

 Lamp, so called after the inventor. By turning a stop-cock 

 in this lamp you let a current of hydrogen strike upon a 

 bit of spongy platinum, and you have the result just men- 

 tioned. In Fig. 99 you have a plan of this lamp, a being a 

 glass jar covered by a brass lid, e, which has 

 a stop-cock, c, with its opening opposite to 

 a brass cylinder, d, which contains the 

 spongy platinum. There is a small bell-jar, 

 /, communicating at the top with the stop- 

 cock, and having suspended in it a cylinder 

 of zinc, z. "When the lamp is to be used the 

 jar, a, is two thirds filled with a mixture of 

 one part sulphuric acid and four parts wa- 

 ter, as indicated by the circular line. As 

 the bell-jar is open at the bottom, the acid 

 and water attack the zinc in it, producing hydrogen gas, 

 just as it is produced in the apparatus described in 143. 

 If the cock be opened the hydrogen gas will escape, and be 

 directed against the spongy platinum in c7, and will make 

 it red-hot, and then this will set fire to the gas. 



386. Other Illustrations. This curious property is not 

 confined to spongy platinum, but the 

 metal in its ordinary condition shows it 

 to some extent. For example, if some 

 ether be poured into a glass jar, Fig. 100, 

 and a coil of platinum wire recently ig- 

 nited be put into it, the metal will glow 

 so long as there is any ether present. 

 Ozone is formed at the same time. In 

 Fig. 101 (p. 273) you have essentially 

 Fig. 100. the same experiment in a prettier form. 



Fig. 99. 



