26 



COALFIELDS AND COLLIERIES Ol' AUSTRALIA. 



facilitating its disintegration. A coal which crumbles on ex- 

 posure to the weather, or which will not readily bear trans- 

 port must be used near its place of occurrence, and should 

 be used soon after it is mined. 



Evaporative Power. This is determined in Australia by 

 means of Thompson's calorimeter, but for more accurate work 

 Mahler's bomb calorimeter may be used. 



Thompson's calorimeter, Fig. 14, consists of a glass cylin- 

 der (a) closed at the lower end; (b) is a cylindrical copper 

 vessel called the condenser, open at the bottom 

 and also perforated with holes (b 1 ) near the 

 open end, the top of the condenser is closed 

 except for a tube with a stop cock (c) at the 

 upper end ; (d) is a metal base to which (b) is 

 fixed by means of three springs attached to 

 (d } . but not shown in the figure ; a series of 

 holes are arranged round the circumference of 

 (d) to facilitate raising the apparatus through 

 the water; (e) is a copper cylinder called the 

 furnace, closed at the lower end only, which 

 fits into a metal ring or seat in the centre of 

 (d). Thirty grains of dry finely-powdered coal 

 is mixed with 10 to 12 times its weight of a 

 mixture made of 3 parts chlorate of potash and 

 1 part sodic nitrate, which, being hygroscopic, 

 must be kept dry : this mixture gives oft' 

 enough oxygen to burn the coal without any 

 access of air. The charge is placed in the 

 the furnace (e) and a touch cord, made b\ 

 passing a piece of string through a saturated 

 solution of nitre or nitrate of lead and dried at 

 212deg. F., is inserted for about an inch into 

 the material, leaving sufficient outside to burn 

 without touching the mixture while the ap- 

 paratus is being subsequently dipped under 

 the water. The glass cylinder (a) is filled with 

 water up to the mark, and its tempera- 

 ture noted: the furnace with its charge 

 and touch cord placed in the socket of the 

 metal base (d), the touch cord ignited, and then the furnace is 

 immediately covered with the cylinder (b), the stop cock at 

 the end of the tube beinir turned off. The whole is lowered 

 into tlie water and kept there until combustion is completed, 

 hot gases bubbling uy, through the holes and warming the 

 water. When deflagration has ceased, the instrument is 

 moved up and down to stir the water, and the stop cock is 

 opened, when water fills the vessel. The temperature of the 



