PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 347 



Prof. Seely.— The more I think of the matter, the more am I amazed at 

 what chemistry enables us to do. If you bring us a candle we do not need 

 to light it in order to tell you what it is worth. A hydrocarbon, to give 

 the most light, should have the hydrogen slightly in excess. If the carbon 

 is in excess there will be smoke. It has been frequently talked over here 

 and is now generally understood, that the light comes from the carbon, 

 heated to a white heat. It may, perhaps, be more easily comprehended il 

 it is presented thus : Suppose we had a quantity of carbon, in the form 

 of coal for instance, which we wished to burn in the way to get the most 

 light from it possible, how should we wish to arrange it ? We should 

 want it in a thin stratum so as to expose a large surface, and we should 

 wish to keep it hot as long as possible before it was burned, for as soon as 

 combustion took place it would be converted into invisible gas, and would 

 cease to give out light. Finally, we should want it in small pieces, so that 

 the light might be soft to the eye. We have no means of arranging car- 

 bon in this way. But nature makes the arrangement beautifully. By 

 combining atoms of carbon with atoms of hydrogen, which separate at a 

 lower temperature than carbon will burn at, the carbon is heated before it 

 is burned; and as the hydrogen occupies much more space than the carbon, 

 the carbon atoms are enveloped by the hydrogen, and thus kept from burn- 

 ing until the hydrogen is consumed. The burning, too, is confined to an 

 excedingly thin film on the outside of the blaze, and thus the illuminating 

 power of the carbon is fully utilized. 



Mr. Chairman, we have had a very grand exhibition this afternoon ol 

 combustion of illuminating materials. Some 18,000 barrels of petroleum 

 oil have been burning in Williamsburgh, and if it had occurred in the night, 

 I have no doubt that we should have had the finest illumination that has 

 ever taken place. As it was, the smoke, as seen from the lower part of the 

 city, made the most magnificent spectacle that I have ever seen. The 

 Express says that the fire originated from an explosion which occurred in 

 one of the vessels which were lying at the wharf discharging petroleum. 

 The account says that after the explosion in the vessel, a barrel on the 

 wharf exploded, and the word explosion occurs half a dozen times in the 

 account. I have no doubt that we shall have a discussion in the papers 

 whether petrolium will explode. Some people seem to think that if you 

 touch a match to a cask of petroleum it will go off like gunpowder, and 

 there is quite a common notion that rock oil will explode. It will not do 

 it. The explosion occurs in this wise : Petroleum has the property above 

 all liquids of passing through capillary tubes. If you put it into a 

 wooden barrel it will go right through the staves, and the barrel will be 

 greasy directly on the outside. The most volatile portion passes through 

 the most readily, and when this, in the form of vapor, is mingled with the 

 atmosphere in a confined place, as the hold of a vessel, an explosive mix- 

 ture is formed. Petroleum is not explosive; but a mixture of the vapor of 

 petroleum with atmospheric air is explosive; and this mixture can be 

 formed only in a close chamber. The question is similar to the famous 

 one, " Will saltpeter explode ?" and the answer is analogous. Saltpeter 

 alone will not explode, any more than a stick of wood or a brick; but when 

 saltpeter is mixed with any combustible, the mixture is explosive. 



