ON LIQUID FUEL. 
601 
When the pump is employed for evaporation in vacuo, it is only necessary to 
introduce the liquid into the flask, to which a fresh caoutchouc cork is fitted, 
having only one perforation. The flask may be heated by standing it in warm 
water. 
The cost of a single pump, including the leaden piping, is stated by Bunsen 
to be eight thalers, or twenty-four shillings. 
ON LIQUID FUEL. 
BY BENJAMIN H. PAUL, ESQ. 
[Concluded from page 554.) 
In order now to arrive at some estimate of the advantage to be gained in a steam 
vessel, either in point of weight to be carried, or space occupied by liquid fuel as com¬ 
pared with coal, it is evident that 100 tons of petroleum, or coal oil, would do the work 
of about 140 tons of good coal. But as coal is rarely burnt in such a way as to be 
rendered useful to its full capability, and as there is always a considerable waste in the 
shape of dust and cinders, which would not be the case with liquid fuel, a further al¬ 
lowance must be made for this. Assuming that one-fifth of the coal is wasted in this 
way, then the equivalent of 100 tons of oil would be 175 tons of coal, for, taking the 
density of the oil as ’850, it would occupy about the same space as an equal weight of 
coals, or at the rate of about 53 pounds per cubic foot. This difference would enable a 
vessel capable of carrying coal for twelve days’ steaming, to carry oil for twenty-one 
days. In burning this oil there would be a saving of labour in stoking, and as it would 
not give any ashes, a great deal of trouble would be saved in that way. 
These results differ widely from the statements which have been made in reference to 
the relative efficiency of oil and coal, according to which it has been represented that 
one ton of oil was equal to from four to five tons of coal,* * * § and that in regard to stow¬ 
age-room the saving was “ more than nine-tenths in bulk ” !f It is true that those who 
have propounded these views have not arrived at them by a consideration of the data I 
have above referred to, and if I may judge from remarks lately made at the meeting 
of the Institute of Naval Architects,! they would appear to deny the applicability of 
those data for determining the question between coal and oil as fuel. Such a denial, 
however, would be of little account if it be not supported by adequate evidence of re¬ 
sults, such as those which have been so much dwelt upon, being really obtainable ; and 
although this subject has now been some years before the public, I am not aware of 
any evidence having yet been brought forward, such as would call for, or justify the 
abandonment of those well-established principles by which the heating power and 
efficacy of fuel is determined, as above stated.§ 
The results of the experiments made at Woolwich, under the superintendence of Mr. 
Trickett, the Engineer-in-Chief of the Dockyard, give, as the highest evaporative effect 
obtained with petroleum, 11 ’63 pounds of water converted into steam per pound of oil 
burnt. In this case, however, the combustion was imperfect. But in the most suc¬ 
cessful trials with coal oil and shale oil, when very little smoke was given off, the eva¬ 
porative effect was about 18 pounds of steam produced per pound of oil burnt. In this 
* See ‘ Journal of the Royal United Service Institution,’ ix. 68. “Petroleum as Steam 
Fuel,” by Capt. J. H. Selwyn, R.N.; also C. J. Richardson, p. 70. 
t Ibid, p, 69. ! See ‘ Engineer,’ 10th April, 1868, p. 257. 
§ Since writing this paper I have learnt that the same subject was discussed by Professor 
W. J. M. Rankine, at the United Service Institution, about a year ago, and I have great 
pleasure in referring to the opinions of such an authority in confirmation of the views I have 
expressed in regard to “Liquid Fuel.”—[“On the Economy of Fuel,comprising mineral oils.” 
‘ Journal of the United Service Institution,’ xi. 218.] The very lucid and exhaustive expo¬ 
sition, given by Professor Rankine, of the conditions which determine the theoretical evapo¬ 
rative power of fuel ought to have been sufficient to prevent any continuance of misconceptions 
as to the possibility that the evaporative effects realized with fuel can exceed or even equal 
the extreme calculated power it is capable of producing. 
