COAL ANALYSIS. 2o 



pact mass of more or less strength. AVheii coke is made in 

 quantity the product is firmer and more coherent than when 

 inaHe on a small scale. 



To determine the comparative strength of cokes use llich- 

 ter's method. The strength is expressed by the multiple of 

 0.1 gram of powdered quartz that is necessary to mix with 

 1 gram of coal to weaken the resulting coke sufficiently to 

 enable half a kilo (l.llb.) to crush it. It is also necessary 

 to examine the physical properties of a coke, its hardness, 

 porosity, etc. 



Specific Gravity. The apparent specific gravity may be 

 determined as follows: Select a suitable piece of dry coal, 

 free it from dust and suspend by a silken thread from the 

 pan of the balance : determine its weight in the air. Then 

 soak it in distilled water, brush off any air bubbles that cling 

 to the surface, and weigh the specimen again while immersed 

 in water, taking care that it hangs freely. This specific gravity 

 is then found by dividing the weight of the coal in air by the 

 difference in weight of the specimen in air and water. Or 

 about 30 grams of dry and weighed coal may be placed in a 

 500 c.c. glass jar closed with a screw cap and rubber gasket. 

 In the middle of the screw cap is an opening 0.6 c:m. in diam- 

 eter, and the cap is sprung so as to make this opening the 

 highest point. Fill the jar with water to a level across the 

 opening in the cap. Draw out 150 c.c. with a pipette, then 

 take off the cap and drop in two or three pieces of coal. Screw 

 the cap on again and take every precaution to see that the 

 cap is screwed to exactly the same mark as before. Water 

 is then added from a burette till the opening in the cap is 

 filled. Taking 1 gram of water to equal 1 c.c., then the 

 apparent specific gravity is the weight of the cubic centimetres 

 displaced by the weight of the coal taken. 



To find the actual specific gravity, weigh 3.5 grams of 

 dried and finely pulverised coal and place it in a 50 c.c. specific 

 gravity flask. Fill the flask about 2-5ths full of water: attach 

 to an aspirator and gently boil on a water bath under a partial 

 vacuum for 2J to 3 hours. The flask is then detached, cooled, 

 filled with water and weighed, and the temperature of the 

 water taken as soon as weighed, so as to enable corrections 

 for temperature to be made. 



A knowledge of the strength of a coal is valu- 

 able, for if soft, an undue proportion of slack is 

 made while mining; and in subsequent handling and trans- 

 port, even the lumps become broken up and form much dust. 

 Too much dust in a coal causes an excessive loss of coal 

 through the fire bars, and may prevent the access of air neces- 

 sary for complete combustion. Should the coal be required 

 for coking, then its soft nature is rather an advantage, as 



