30 COALFIELDS AND COLLIERIES OK AUSTRALIA. 



bulk for the same weight, and so occupies less bunker room 

 on board ship. If the increased specific gravity of a coal is due 

 to non-combustible material, then, of course, it becomes dele- 

 terious. By means of the specific gravity of a coal, we can 

 ascertain the weight of a cubic foot of it, or how many cubic 

 feet go to the ton, and how many tons per acre an inch in 

 thickness represents. A seam of coal having a specific gravity 

 of 1.3 will contain about 130 tons per acre for every inch in 

 thickness. Allowing for moisture, pillars and waste, 100 tons 

 per acre per inch is a close approximation to the probable yield. 

 We must distinguish between the apparent and the actual 

 specific gravity : the former is the specific gravity of a piece of 

 coal, the pores of which are not filled with water: the latter is 

 the specific gravity of the coal with all the air driven out. 



By specific gravity is meant the weight of a body as com- 

 pared with the weight of an equal bulk of the standard body 

 which is reckoned as unity. Pure water at OOdeg. F. is taken 

 as unity. A cubic foot of distilled water weighs 62.3211b. 



Heating Power of Coals. 



In Great Britain and the United States of America the unit 

 of heat adopted is the British Thermal Fnit (B.T.U.) This is 

 the amount of heat required to raise the temperature of one 

 pound of pure water through one degree Fahrenheit at or near 

 39.1 deg. Fahr., the temperature of maximum density of 

 water. 



On the Continent of Europe the French Thermal Unit or 

 calorie is employed, which is the quantity of heat required to 

 raise the temperature of one kilogramme of water one degree 

 Centigrade, at or about 4 deg. C. One French calorie equals 

 3.968 B.T.U., and 1 B.T.U. equals 0.252 calories. According 

 to the determinations of Favre and Silbermann, the complete 

 combustion of a kilogramme for calories, or a pound weight 

 for B.T.TJ. of the following substances develop the accom- 

 panying heats : 



*H to H.O 34,462 calories = 62,032 B.T.U. 

 C to C0~ 8,080 calories = 14,544 B.T.U. 



CO to CO* 2,403 calories = 4,325 B.T.U. 

 S to SO, " 2,220 calories = 3,996 B.T.U. 

 From these we are enabled to calculate the theoretical values of 

 any fuel from its chemical composition, due allowance being 

 made for the hygroscopic water present in the fuel. tDulong 



^Chemistry, Theoretical, Practical and Analytical, as ap- 

 plied to the Arts and Manufactures, Div. IV., page 896 

 (London). 



tPoole (H). The Calorific Power of Fuels (New York) 1898. 



