Twenty-first Annual Meeting. 



43 



riety of average samples was taken from various parts of a mine — block, nut, and 

 slack. These were mixed together and finely powdered. The resulting four or five 

 pounds were considered a fair representative of the coal from that mine, and also 

 had not been selected by interested parties. The burnings were made by Thomp- 

 son's calorimetric method. The apparatus was constructed by Alex. Wright, of Lon- 

 don, and is the one employed by the English Government in the purchase of its coals 

 for railway and marine, as well as by many of the large manufacturers in that and 

 in this country. It is based upon the following principles. The latent heat of water 

 represents the amount of heat which disappears when water at 212° is converted 

 into steam at 212°. This amount is 537.22 gram-degrees or calories. Consequently 

 the number of degrees C. through which 1 gram of coal will raise 537.22 grams of 

 water will be a measure of the evaporative power of that coal. Evidently the abso- 

 lute value of the latent heat of water is immaterial. The apparatus is arranged to 

 produce the complete combustion of 2 grams of coal in 1,934 grams of water. To 

 effect this perfect combustion, the coal, powdered to pass through a sieve 1,000 

 meshes to the square inch, is intimately mixed with about 22 grams of KCIO;, and 

 KNO3, three parts to one. This mixture, in a small copper cylinder, is covered with 

 a larger copper cylinder like a diving-bell, with a series of holes around its base. 

 The mixture is ignited by a fuse, the copper furnace covered with the larger cylin- 

 der, and the whole is plunged under the water. The KCIO3 and KNO, furnish oxy- 

 gen for the complete combustion of the coal, the gaseous products forcing their way 

 in bubbles up through the water. In their ascent the bubbles are robbed of their 

 heat by the water. Upon completion of the burning, the rise of temperature is de- 

 termined by an accurate thermometer. A description of this method of Thompson 

 is given in the Encycloptedia Britannica, under the head •'Coal." The corrections 

 Tipon the instrument have been determined by experience and theory, as follows: 



1. Loss of heat from radiation, conduction, and correction. The calorimeter jar 

 was tilled with water about 6°F. above the temperature of the room, and its rate of 

 •cooling determined. The refinement of the experiment does not require either 

 Newton's or Dulay <fc Petit's Law of Cooling. The following table gives the results: 



lh.35m. Drop of 3. 9° F. 



The loss is quite uniformly 0.03° F. in 1 minute. A burning requires about 3 

 minutes; hence the loss would be 0.1° F. 



This loss is approximately compensated for by having the water in the calorimeter 

 as much below the room-temperature before the burning as it is above at the close 

 of the experiment. 



2. Heat absorbed by metallic parts of the calorimeter. These parts weigh about 

 0.5 kilograms, with a specific heat of 0.095. 8ince there are approximately 2,000 

 grams of water, 2.4 per cent, must be allowed for absorption by the calorimeter. 



3. Heat absorbed by the gases of combustion. This amount can be only approx- 

 imated. The volume of the escaping gases is about 3,300 cubic centimeters. The 

 xate of combustion is slow enough to allow these gases to issue into the air at about 

 the temperature of the water, or about 5.4° F. above the room-temperature. Assum- 



