496 Coal Washing. [Oct., 



or more rows of narrow trenches, communicating with each other 

 at alternate ends, somewhat in the following manner. 



Fig. 3. 



„ . r.'TJnik 2"° Tank 



I OutfalL 



o£ waste 



wa-ter 



Sluice 



Here it will be seen advantage is taken of the known tendency 

 of any obstruction in the flow of water to cause it to deposit what- 

 ever matter it may hold in suspension. The total area of tanks 

 required for any coal-washing works must depend upon the extent 

 to which it is proposed to carry on such work, as well as in some 

 measure upon the available amount of water for the purpose ; it 

 would, therefore, not be jDOSsible to lay down any general rules upon 

 that subject, which must be determined after a consideration of the 

 special circumstances of each case. 



The cost of washing coal varies very much at different colHeries, 

 but it may be assumed that, on an average, it should not exceed 

 threepence or fourpence per ton. At some places the washing is 

 done by contract, one man receiving a certain sum for each ton of 

 coal washed, and providing all the labour necessary, and paying all 

 expenses connected with the operation. At other establishments, 

 the engine employed to drive the washing machine may, perhaps, 

 also be connected with other machinery, although it is better, in all 

 cases, that it should have an independent engine for its own use. 

 Under such circumstances, the cost of working the engine would be 

 borne by the proprietors, and the person contracting would, of 

 course, not be entitled to receive so high a price as if he were 

 responsible also for the whole duty of the engine. 



The practice of coal washing is, as we have ah-eady explained, a 

 comparatively modern introduction in the economy of colliery 

 management ; but so rapid has been its extension within the last 

 few yeai's, that it is now coming into very general use. The 

 advantages of thus purifying the slack of our coal mines are 

 numerous, and calculated to benefit alike the producer and the 

 consumer ; for whilst it j^ractically extends the available yield of our 

 coal beds, it should have the effect of checking any inordinate 

 increase of prices, if it do not actually tend to reduce the cost to 

 the public at which certain classes of coal are now obtainable. 



