CLASSIFICATION OP MINEEAL LANDS. 107 



Since the value of the land varies with the quality of the coal as 

 determined by the chemist, his methods are briefly described here.^ 

 Immediately after the sample is received at the laboratory it is 

 weighed and placed in a shallow tin pan in a large drying oven, in 

 which a temperature of 30° to 35° C. is maintained. The sample 

 remains exposed to currents of warm air in the oven until the loss 

 between two successive weighings made six to eight hours apart does 

 not vary more than 0.2 per cent. The loss of weight in the oven is 

 called air-drying loss. 



After being air dried the sample is crushed to a fine powder and 

 thoroughly mixed. To determine the amount of moisture remaining 

 in the coal after air drying, a 1-gram sample is heated for an hour 

 at 105° C. and then cooled in a desiccator over sulphuric acid. The 

 moisture in the sample is thus driven off, hence the percentage of 

 loss represents the percentage of moisture in the coal. The remain- 

 ing part of the sample is next used to determine the amount of ash 

 in the coal. This determination is made by slowly heating the 

 sample in a muffle furnace until all of the combustible matter is 

 burned off. The remainder is ash. The volatile matter is deter- 

 mined from a fresh 1-gram sample in a 30-gram platinum crucible, 

 with a close-fitting cover, heated for seven minutes over a Bunsen 

 flame 20 centimeters high. The loss in weight minus the moisture at 

 105° C. is the weight of the volatile combustible matter. The sulphur 

 is determined on a separate example by what is known as the Eschka 

 method. The percentage of fixed carbon given in the analysis is the 

 difference between 100 per cent and the sum of moisture, volatile 

 combustible matter, and ash. 



The calorific value of a coal, or the amount of heat that can be 

 obtained from it, is the most important factor in classification and 

 valuation. 



The calorific value of coal is determined with a bomb calorimeter. 

 The following is a brief description of the details of operation : 



A 1-gram sample of coal (60-mesh) in a platinum tray is placed 

 in the bomb and the lid is screwed down tightly against a lead 

 gasket. Oxygen is forced into the bomb until the pressure is 18 to 

 20 atmospheres. The bomb, filled with oxygen, is placed in a brass 

 bucket containing distilled water, the bucket having been previously 

 placed in an insulated jacket. 



The coal is ignited by electric current and is burned at once. The 

 heat of combustion is transmitted through the walls of the bomb and 

 is manifested in a rise in the temperature of the water. This rise 

 in temperature is measured by a very delicate thermometer. The 



1 The methods of analyzing coal and coke are fully described in Technical Paper No. 8, 

 Bureau of Mines, by Frederick M. Stanton and Amo C. Pieldner. The method outlined 

 here Is summarized from that paper. 



