MR. H. BRKKETON BAKER ON COMBUSTION IN DRIED OXYGEN. 573 



the carbon was considered sufficiently pure for the experiments. It was kept in a 

 small stoppered bottle, but, as this involved exposure to a small quantity of air, it was 

 thought advisable before the carbon was used for the preparation of each experiment 

 that the portion taken should be heated to redness in a vacuum. This served not 

 only to dry it, but also to free it from occluded oxides of carbon which are products of 

 its slow combustion in air at ordinary temperatures. 



The oxygen was prepared by heating pure potassium chlorate, and was stored in 

 gas pipettes over previously boiled mercury. In the gas were placed plugs of phos- 

 phorus pentoxide. These plugs were made thus : A piece of glass tubing, 1 cm. in 

 diameter, and a longer piece of glass rod, exactly fitting it, were heated to dry them 

 thoroughly. The tube while still warm was pushed to the bottom of the bottle 

 containing the pentoxide, and the portion of the latter so introduced was compressed 

 by forcing the glass rod into the tube like a piston. Both tube and rod were then 

 removed from the bottle, with the plug almost entirely protected from the air. The 

 tube was then quickly plunged under the mercury, through the tubulure of the 

 pipette, and the piston pressed down. The plug was thus pushed out of the tube, 

 and rose through the mercury into the oxygen which was to be dried. This plan of 

 dealing with the phosphorus pentoxide, in the form of a compact cylinder, was 

 extremely useful when it was necessary to introduce it into glass tubes which were to 

 be drawn out in the blow-pipe flame. If only a small quantity of the oxide adheres 

 to the portion of the glass to be heated, it diminishes the ductility to a remarkable 

 degree, and renders it extremely brittle. 



Carbon heated in contact with Platinum. 



A mixture was made of platinum black (previously heated to redness in a vacuum) 

 and the pure charcoal. A hard glass tube was slightly contracted in the middle, and 

 heated in a current of dried air to dull redness, to get rid of the moisture which 

 clings so tenaciously to glass. On one side of the constriction was introduced the 

 mixture of platinum and carbon, and on the other plugs of phosphorus pentoxide. 

 Oxygen was passed through the tube and the ends sealed. The oxygen was left 

 drying for six weeks. At the end of this time the part of the tube containing the 

 mixture of carbon and platinum was heated to redness for three minutes with no sign 

 of visible combustion. Analysis showed that the tube now contained 



Carbon dioxide ... 27 per cent. 

 Oxygen 73 



A second experiment, in which the oxygen was dried for three weeks, and the 

 mixture of carbon and platinum was heated for four minutes, gave 



Carbon dioxide ... 34 per cent. 

 Oxygen 66 



