552 
ON LIQUID FUEL. 
of gas discharged into the chimney would be about three and a half times as great as in 
the combustion of an equal weight of carbon. This larger quantity of gas will, however, 
contain nearly four times as much effective heat as that resulting from the combustion 
of aD equal weight of carbon, and its temperature will be about 270° higher, so that in 
this respect the use of fuel containing a large amount of hydrogen, provided it can be 
perfectly and readily burnt, presents an advantage as compared with fuel consisting 
almost entirely of carbon. Eather more than one-fourth of a pound of hydrogen would 
give as much effective heat as one pound of carbon with a somewhat smaller volume of 
combustion products. The extent to which this advantage affects the value or efficiency 
of fuel will, of course, depend on the amount of hydrogen it contains. Since no hydro¬ 
carbon available as fuel contains more than 15 per cent, of hydrogen, the actual evapo¬ 
rative efficacy of such a material, when used under the ordinary conditions, cannot, at 
the utmost, be more than about 40 per cent, greater than that of an equal weight of 
carbon. This, assuming it to be perfectly burnt, and the arrangement of boiler-flues or 
tubes, etc., to be favourable for the transfer of heat, is the maximum effect to be looked 
for according to the data already given. 
The amount of hydrogen in petroleum is probably larger than in any of the other 
hydrocarbons proposed to be used as fuel, and that contains, on the average, about 13 
per cent. In coal and shale oil the amount of hydrogen is less. Consequently, the 
evaporative efficacy of these materials, as compared with carbon, would not reach the 
above limit of 40 per cent, in excess. The ratio between these materials and ordinarily 
good coal is much about the same in regard to evaporative efficacy, since the hydrogen 
contained in coal compensates for the oxygen and ash it contains, unless the amount of 
these is very considerable. 
The tables in next page show the relation between the total heat of combustion and 
the available heat of hydrocarbons, containing respectively 14 and 25 per cent, of 
hydrogen, as the amounts of heat consumed in the furnace gas, and the mode in which 
it is disposed of. 
I am not aware of any liquid hydrocarbon applicable as fuel, which contains so much 
as 25 per cent, of hydrogen, so that an evaporative effect of about 16 pounds of steam 
per pound of hydrocarbon burnt must be regarded as the maximum result to be attained 
with such material used as fuel. By burning these hydrocarbons with only just enough 
air for combustion, or half the qualities assumed to be supplied in the above estimations, 
the effect capable of being realized would be from 13 to 14 per cent, greater than in the 
case stated above, or about 18 pounds of steam per pound of hydrocarbon containing 14 
to 15 per cent, of hydrogen. 
The plan of using liquid fuel, which so far as I am aware has proved the most advan¬ 
tageous, is one which does, to some extent at any rate, secure the advantage to be gained 
by forcing air into the furnace. According to this plan the oil is supplied to the furnace 
through a small pipe, together with a jet of high pressure steam, by which it is con¬ 
verted into spray, much in the same manner as, in the toy known as the perfume 
vaporizer, a liquid is blown out of a bottle by a current of air. The steam-jet at the same 
time induces a current of air which mixes with the oil spray and supports its combustion. 
This is the arrangement used by Messrs. Field and Aydon, and it appears to work exceed¬ 
ingly well, effecting a very perfect combustion of the oil. The oil I have seen used in this 
way was the dead oil, or creasote oil, which is a refuse product in the refining of gas- 
tar. It possesses characters which render it much preferable to petroleum, or to the oil 
obtained by distilling coal at a low heat for use as liquid fuel. In the first place, its 
density being greater than that of water—the gallon weighing about 12 pounds—i 
takes less space for stowage than petroleum or coal oil, the gallon of which weighs onk 
from 8 to 8^ pounds. For the same reason it would not be so dangerous as the lighter 
oils in case of accident; for instead of floating on the surface of water and burning, it 
would sink harmlessly. Again, its very high boiling-point, approaching to a red heat, 
and the great density of its vapour as compared with that of petroleum or coal oil, are 
great advantages as regards risk of explosion in consequence of the oil-vapour becoming 
mixed with air, and then catching fire. This could hardly take place with the dead oil, 
except at a very high temperature, while petroleum readily gives off vapour to the air at 
a moderate degree of heat. 
One pound of hydrocarbon, containing 14 per cent, of hydrogen, yields about 31 
pounds of furnace gas, consisting of:— 
