770 



The next table shows the calorific power and evaporative efficacy of liquid fuel as 

 compared with coal. 



Thus oils may effect a saving of from 35 to 40 per cent, of the space occupied by a 

 coal of equal steam-producing power. Not only would more space be available for 

 cargo, but also fewer hands would bo required. And in war-ships, steam would be 

 more quickly raised ; they could sail without smoke, and could keep to sea for a longer 

 time. But against this, most of the oils proposed to be employed give off vapours 

 even in the cold ; and these, when mixed in certain proportions with the atmosphere 

 are violently explosive. Then relative price must always be a great stumbling-block 

 in the introduction of this new agency ; when coal rises to 51. or 6^. per ton the 

 average prices of crude mineral oil or petroleum, the question will be a practicable 

 one. Improvements in retorts, cheapening the cost of crude mineral oil, will also 

 obviate this difficulty. [See PARAFFIN.] Creasoto, estimated as worth 22s. per ton, 

 has been advantageously used as a liqxiid fuel. 



To use liquid fuel effectively, perfect combustion immediately under the steam- 

 boiler must be obtained, so that smoke is prevented and the full heat or evaporative 

 capacity of the fuel realised. The best coal-oils rarely contain more than 30 per cent, 

 of volatile matter ; but in those most suitable for steam fuel the quantity is very much 

 less. 



Eichardson's method of applying liquid fuel was tested at the Woolwich Dockyard 

 on July 6, 1866, under the supervision of Mr. Lloyd, engineer-in-chief of the Navy. 

 The rationale of this plan is to employ steam-jets with the application of liquid fuel 

 below the steam-boiler. In these trials much smoke was produced, and the tubes of 

 the boiler rendered very foul by deposition of soot in them. The average results gave 

 an evaporation of 13'2 Ibs. of water per 1 Ib. of oil consumed ; the variations ranged 

 from 7 - 14 Ibs. to 18'38 Ibs. of water; treated from 100 to 212 F. ; and converted 

 into steam at 212 F. In the most successful trials the evaporation was very low. 

 Now average results have been obtained with coal of an evaporation of 8 Ibs. of water 

 to 1 Ib. of the fuel, and much higher figures are not exceptional. 



In Field's improved method, the oil flowing from a reservoir is projected into the 

 heating furnace below the boiler along with a jet of high-pressure steam, introduced 

 in the form of spray. As many as 19 Ibs. of evaporative power have been quoted as 

 the fruit of this patent, but 13 to 16 Ibs. of water evaporated per Ib. of oil consumed, 

 are likelier figures. 



By Dorsett's patent the oil is first vaporised before entering the heating furnace ; 



1 It is assumed that these oils are burned with only just enough of air for the purposes of combus- 

 tion, and that the fnrnace-gfts is discharged at 600 F. 



* The coal is burnt as usual, with twice the air necessary for combustion. 



1 The evaporative duty given in the above and subsequent table is probably higher than that 

 actually obtained on an average in steam-vessels to the extent of 20 per cent. ; the actual duty ob- 

 tained being usually seven pounds of water converted into steam per Ib. of conl. 



The following table exhibits the relative efficacy of liquid fuel and coal as steam fuel, in relation to 

 the space they occupy respectively : 



