| Moisture at 100° C. | __ | per cent. |
| Volatile matter | __ | " |
| Fixed carbon | __ | " |
| Ash | __ | " |
| contains sulphur __ per cent. |
Determination of Sulphur.—The sulphur exists in the coal partly in organic combination, partly as metallic sulphide (iron pyrites, marcasite, &c.), and, perhaps, as sulphate. So that the sulphur determination must be separately reported, since a portion will go off with the volatile matter, and the remainder would be retained and weighed with the coke.
The sulphur is thus determined:—Take 1 gram of the coal and mix with 1.5 gram of a mixture of 2 parts of calcined magnesia and 1 part of carbonate of soda, and heat in a platinum crucible for one hour or until oxidation is complete. Turn out the mass and extract it with water and bromine, filter, acidulate with hydrochloric acid, boil off the bromine, and precipitate with baric chloride (estimating gravimetrically as given under Sulphur). Another method is as follows:—Take 1 gram of the coal and drop it gradually from a sheet of note paper on to 5 grams of fused nitre contained in a platinum dish. Extract with water, acidify with acetic acid, and estimate volumetrically as described under Sulphur.
Calorific Effect of Coals.—The heat-giving value of a coal is best expressed in the number of pounds of water, previously heated to the boiling point, which it will convert into steam. This is generally termed its evaporative-power. It may be determined by means of the calorimeter (fig. 73). This consists of a glass cylinder marked to hold 29.010 grains of water. The instrument consists of a perforated copper stand, provided with a socket and three springs. The socket holds a copper cylinder which is charged with 30 grains of the dried coal mixed with 300 grains of a mixture of 3 parts of potassium chlorate and 1 part of nitre. The charge is well packed in the cylinder and provided with a small fuse of cotton saturated with nitre. Fill the glass cylinder to its mark with water and take the temperature with a thermometer marked in degrees Fahrenheit. Ignite the fuse and immediately cover with the outer copper cylinder (extinguisher-fashion), which will be held in its place by the springs. The stop-cock should be closed before this is done. Place the apparatus quickly in the cylinder of water. When the action is over open the stop-cock and agitate the water by raising and lowering the instrument a few times. Again take the temperature. The rise in temperature, plus 10 per cent. for the heat used in warming the apparatus and lost by radiation, gives the evaporative-power.
The following is an example:—
| Temperature before experiment | 67.0° | F. |
| Temperature after " | 79.0° | " |
| ———— | ||
| Rise | 12.0° | " |
| + 1/10th | 1.2° | " |
| ———— | ||
| Gives | 13.2° | " |
One pound of the coal will evaporate 13.2 pounds of water.