FUMES AND OTHER PRODUCTS. 127 



"Yes," said John; "of course I mean an English six- 

 pence. I saw it in a window, and I went in and bought 

 some of it ; I am going to burn it, and make a bright light ; 

 of course I am not going to burn it all at once, here ; I am 

 only going to burn a small piece half an inch long, per- 

 haps, just for an experiment, and the rest I'm going to take 

 to America." 



Lawrence approved of this arrangement, and it was 

 agreed that they would try the experiment that evening 

 after dinner. 



There was some question about the fumes which might 

 arise, but Lawrence said he thought that there would be 

 no fumes, as the product of the combustion of magnesium 

 was simply magnesia, which was a harmless white powder; 

 in other words, a finely comminuted solid. Fumes arose 

 from combustion, he said, only when the products, or some 

 of them, were gaseous, so that they might rise and float in 

 the air. 



It is true that sometimes, when the products of the com- 

 bustion, or the substances set free by it are solid, they are 

 developed in the form of a powder so fine as to be borne 

 upward by the current of hot air, so as to produce the ap- 

 pearance of fumes, and sometimes they mingle with true 

 fumes actually produced. This happens very strikingly in 

 the case of the combustion of wood or coal, in which very 

 fine particles of carbon, detached from the substance of the 

 wood or coal, are carried up among the fumes of carbonic 

 acid gas and the vapor of water, which are really the pro- 

 ducts of the combustion. 



Now combustion, as probably the readers of this book 

 remember, is only the rapid combination of a substance 

 with the element called oxygen, which exists abundantly 

 in the air, and has such an eager affinity for many other 

 substances, especially when they are heated up to a certain 



