574 MR. II. HUKKKTON BAKER ON COMBUSTION IN DI'.IKI) OXYtiKX. 



The quantities of carbon burnt in these two experiments do not differ greatly from 

 the quantity of carbon burnt under similar conditions when no platinum was present. 

 There is, however, this important difference between the two cases, that in the 

 presence of platinum only carbon dioxide is produced.* In the absence of platinum 

 varying quantities of carbon monoxide were formed, generally exceeding in amount 

 the carbon dioxide produced at the same time. 



A third experiment was made with carbon in contact with platinum. The 

 charcoal was in the form of a rod, about 4 cm. in length. It was enclosed in a coil of 

 fine platinum wire, which had been previously freed from hydrogen by heating to 

 redness in oxygen. The ends of the coil were attached to thicker platinum wires, 

 which were sealed into two pieces of quill tubing. These passed through two holes in 

 an india-rubber stopper which fitted into the neck of a small flask (fig. 1). The flask 



*. 1- 



contained pure oxygen, dried by plugs of phosphorus pentoxide placed in the flask. 

 A small quantity of mercury covered the stopper, to prevent diffusion of water vapour 

 through its mass. The gas was left drying for fourteen days. 



The platinum coil was heated by an electric current to a bright red heat. The 

 carbon did not catch fire, and the glow disappeared directly the current was stopped. 

 With a stronger current, the platinum was heated nearly to whiteness ; the carbon 

 showed visible combustion for two seconds, after which the glow died out. On 

 analysing the contents of the globe after the experiment, more than half the gas was 

 found to be oxygen. 



A similar experiment was tried with a rod of carbon in moist oxygen. On raising 

 the temperature to dull redness by means of the heated wire, the carbon caught fire, 

 and, although the current was immediately broken, there was no cessation of the 

 combustion until the rod was entirely .consumed. 



These results point to the conclusion that the contact of platinum does not cause 

 the union of dry carbon with dry oxygen, but only influences the products of 

 combustion. 



* It has been proved that dry carbon monoxide and oxygen unite readily without flame in presence of 

 red-hot platinum (DixoN and LOWE, " Chem. Soc. Joarn.', 1885, Trans, p. o75). 



