1094 



WATER 



Many seams of coal already sunk to, or portions of seams in -work, aie left under- 

 ground as unsaleable in consequence of the impurities they contain. Small coal sells 

 at a low price chiefly in consequence of its impurities and the defective coking pro- 

 perty -which they occasion. It has been estimated that an amount not far short of 

 the quantity of coal sold is sacrificed in producing a commercial article of adequate 

 quality and description. The enormous consumption of coal in this country, amount- 

 ing to 127 millions of tons per annum, renders the utilisation of a larger portion of 

 the more valuable seams now in course of being exhausted, and the bringing into the 

 market of other seams, objects of national importance. 



The "differences between the specific gravities of coal and its impurities, allow of 

 their being separated by the action of water when sufficiently crushed. The water 

 process hitherto most commonly adopted is that known as ' jigging,' which consists in 

 forcing the water alternately up and down through the mass of coal. The downward 

 current of water in 'jigging' is prejudicial, and entails a large sacrifice of the finer 

 particles of the best coal ; whilst the upward current, from its rapidity and irregularity, 

 is costly both in time and power, besides failing to effect the more perfect separation 

 which is obtained by a slow, continuously ascending or pulsating current, regulated 

 to the proportion of shale in the coal, and to the size of the particles to be acted 

 upon. 



Several coal-washing machines have been from time to time introduced, but the 

 machine described sufficiently represents their general character. 



Machines have been established in Scotland, Cumberland, Derbyshire, Gloucester- 

 shire, and Wales, to purify from 20 to 100 tons of coal per day, at a cost not exceed- 

 ing 3d. per ton, and with a loss not exceeding 2 per cent, of coal. 



WATER. (Ettu, Fr. ; Wasser, Ger.) There is no substance so extensively used 

 in the operations of nature on our globe, as well as in the workshops of men, as water. 

 To speak of its numerous relationships, even briefly, would demand, too much space, 

 and it will be needful to confine ourselves strictly to a consideration of its physical 

 conditions. 



A few analyses of river water will convey some idea of the composition of the solid 

 matter held in solution, given in grains per gallon of this fluid : 



Kain is the probable source of all water. It is almost absolutely pure water if it 

 falls through uncontaminated air. Water is almost colourless, brilliant, without taste 

 or smell, and very transparent. When seen through great depths it has a slightly 

 blue shade of colour. It weighs 252-45 grains per cubic inch at 60 Fahr. in the air. 

 The specific gravity of all substances liquid and solid are taken by their relation to 

 water, which is called I'OOO or 1. Its boiling point at 29-92 bar. pressure is 212 

 Fahr. ; it freezes at 32, and it evaporates at all temperatures. Its boiling point at 

 760 meters pressure is called 100 Cent ; freezing point 0. It assumes, therefore, the 

 gaseous, liquid, and solid states with great facility. The specific heat of water at 32 



