COAL ANALYSIS. 21 



and calcium chloride, to absorb the carbon dioxide formed by 

 the oxidation of the carbon : the bulbs and IT tube are weighed 

 together. A final guard tube, filled with calcium chloride and 

 soda lime, is fixed on to the end. The gases formed during 

 combustion are drawn through the train by suction, a Marriott 

 bottle being used to secure a constant suction head. The oxy- 

 gen is ^supplied under a slightly greater pressure than the 

 aspirator, so that there shall be no fear of leakage of the com- 

 bustion gases into the gasometer. 



The sample of coal is well mixed and ground : 2-10ths of a 

 gram are weighed out into a platinum boat, about 70 mm. long 

 and 8 mm. deep, which is pushed into the rear of the combus- 

 tion tube up to the asbestos plug, which holds the copper oxide 

 in place. That part of the tube holding the boat is kept cool 

 till from 20 to 25 c.m. of the copper oxide is at a bright red 

 heat, and the lead chroniate heated to a barely visible red. 

 The burners at the back of and under the boat are then turned 

 on very gradually, and the volatile products slowly driven off; 

 a slow rate of aspiration, one or two bubbles a second, being 

 kept up ; care must be taken not to drive them off so rapidly 

 as to cause back pressure. If the combustion is too rapid, 

 the ash may fuse and retain unburnt coal. The ash must be 

 examined for unburnt carbon. The ignition is characterised 

 by considerable glowing. Oxygen is passed through the train 

 for several minutes after the last evidence of combustion has 

 disappeared, or till it begins to bubble freely through the 

 potash bulbs. About 1200 c.c. air are then aspirated through 

 the train before weighing up. The absorption train is carefully 

 weighed, both before and after the combustion: 100 parts of 

 CO a represents 27.27 parts of carbon: 100 parts of water repre- 

 sents 11.11 parts of hydrogen. 



Sulphur. The total sulphur may be determined by 

 Eschka's method. One gram of the finely powdered coal is 

 mixed by means of a glass rod in a 30 c.c. platinum crucible, 

 with half a gram of the Eschkn mixture which consists of 1 pt. 

 d'ry sodium carbonate and two parts of the light porous variety 

 of magnesium oxide : this is afterwards covered with about half 

 a gram of the Eschka mixture. The crucible is then heated 

 over an alcohol lamp, which is moved about by hand ; gas 

 must not be used on account of the sulphur it contains. At 

 first the flame is kept low, and is scarcely allowed to touch the 

 bottom of the crucible until the volatile matter has been burnt 

 out, which takes from 15 to 30 minutes: the heat is then in- 

 creased, and the contents of the crucible stirred with a plati- 

 num wire till all trace of unburnt carbon has disappeared. 

 As the complete burning of coke over an alcohol lamp is very 

 difficult, the final burning may be done in a gasoline muflfle 

 furnace. The mixture is transferred from the crucible to a 



