MR. H. BRKBETON BAKER ON COMBUSTION IN DRIED OXYGMN 581 



Experiment III. The carbon dioxide was passed over charcoal at 440, the gas 

 being afterwards passed through two sets of potash bulbs, over red-hot copper oxide, 

 and through a third set of potash bulbs to analyse the gases produced. The first set 

 gave an increase in weight of '4548 gram, the second set no increase, and the third 

 set no increase. The experiment lasted four hours. Therefore at these temperatures 

 carbon dioxide is not decomposed by carbon, and the carbon monoxide in the former 

 experiments must have been formed by direct union of carbon and oxygen. 



The question now arises, Does the burning of carbon under ordinary circumstances 

 take place in two stages ? Is carbon monoxide first produced, and this by further 

 oxidation transformed into the dioxide ? The problem seems incapable of direct 

 solution. I venture to advance the following considerations with regard to it : 



I. It has been proved by direct experiment that more carbon monoxide is burnt by 

 air at 500 than at 440. We find, in the results described above, that when carbon 

 is burnt in air at 440, more carbon monoxide appears in the products of combustion 



t than at 500, amounting in one case to 53 per cent. 



II. It has been proved, also, that when the oxygen is diluted with a larger quantity 

 of nitrogen than is contained in air, less carbon monoxide is oxidised, though the 

 oxygen is present in excess. In the experiment already described, by diminishing 

 the percentage of oxygen from 21 to 15, we get a larger quantity, 66 per cent., of 

 carbon monoxide in the products of combustion. 



III. Lastly, by drying the oxygen in which the carbon is heated, the percentage of 

 carbon monoxide is largely increased, amounting in one case to 94 '7 per cent, of the 

 products of combustion. 



And since it is found that, when the conditions of the experiment are made more 

 and more unfavourable for the oxidation of carbon monoxide, (1) by lowering the 

 temperature, (2) by decreasing the proportion of oxygen to nitrogen, (3) by drying 

 the oxygen, we get more and more carbon monoxide produced, are we not justified in 

 assuming that the combustion of carbon first produces this lower oxide ? 



Combustion of Sulphur in Oxygen. 



In the preliminary experiments on the combustion of sulphur in dried oxygen, the 

 sulphur used was purified by repeated sublimations. 



Experiment I. The sulphur was placed at one end of a tube filled with oxygen, 

 phosphorus pentoxide being introduced at the other to dry the gas. The tube was 

 sealed up and left drying for five days. 



The tube was heated by an Argand burner, side by side with a similar tube 

 containing sulphur in moist oxygen. The sulphur began to melt at the same moment 

 in both tubes. Soon afterwards there was a sudden explosion in the moist tube, and 

 a few seconds later a small blue flame appeared on the surface of the dry sulphur. 

 This continued for a short time and was then extinguished On analysing the gases 

 in the two tubes, oxygen was found in the free state in the dry tube, but not in the 

 moist tube. 



