Portable Agricultural Steam Engines at Newcastle. lO't 
hy the union of which with the oxygen of the air the heat of 
combustion is evolved. In the case of the coal there is a little 
sulphur, but this adds only a quite insignificant amount of heat. 
It is usual to speak of oxygen as a thing which in itself is 
non-combustible, but is the supporter needed for the com- 
bustion of other bodies. The fact is, that since the effects of 
combustion are produced, as has just been said, by the union 
of say carbon and oxygen, the oxygen is just as much a com- 
bustible as the carbon is, and the carbon is just as much a 
supporter of combustion when considered in relation to the 
oxygen as a combustible, as the oxygen is a supporter when 
considered in relation to the carbon treated as a combustible, 
and, when needed for simplicity, oxygen will be dealt with by 
us as forming part of the fuel. Now if in a fuel (using the 
word in the ordinary sense) there are found both oxygen and 
liydrogen, it has been demonstrated that these have already 
made their union, and that, therefore, no further chemical 
iction will arise when the fuel is burnt, from the union of its 
bydrogen with the oxygen of the air, because union with 
oxygen has already taken place. Thus there must only be 
^ken as available for the production of heat so much of the 
lydrogen as is in excess of that needed by the oxygen in the 
fuel to combine with it. Thus, in truth, all the hydrogen, 
(vhich has with it its equivalent of oxygen, is inert, as is also 
ts oxygen, and as indeed must be any oxygen in the fuel, 
.vhether accompanied by hydrogen or not, because that oxygen 
inds no hydrogen or other material in the air with which, in 
he burning of the fuel, it can associate. The researches of 
nany eminent chemists have determined with great exactitude 
he quantity of heat developed by the combustion of many 
lubstances. Carbon, when completely burned in air, yields 
;arbonic acid gas, and develops 14,544 units of heat per one 
lound of carbon. Hydrogen burned in the same way, pro- 
iuces water (giving forth 61,200 units of heat), or the vapour 
)f water, and in the latter case develops 52,509 units of heat 
)er one pound. 
Wood similar to that used for rekindling the fire (which 
ekindling is referred to further on) was found, when dried at 
580° Fahr., to have contained 22 per cent, of moisture. 
The dried wood had the following composition : — 
Carbon 49-95 
Oxygen 41-27 
Hydrogen .. .. .. .. : 6-00 
Nitrogen .. .. .. 1-13 
Ash 1-65 
100-00 
VOL. XXIII. — S. S. 3 A 
