MINERAL RESOURCES OF DEVON AND CORNWALL. 199 
work is done. After this the same water is employed for washing 
the ores, and in driving the machinery used in working furnaces 
for the extraction of arsenic and sulphur from the ores, in grinding 
arsenic, in working say-mills, in supplying the boiler of the crushing- 
engine, &c.; and finally the water finds its way back again, after 
having been utilized as much as possible, into the river. All this 
water is raised by one of the large wheels. The work of the other 
wheel is to move a long line of iron rods of immense strength, 
stretching many hundred feet, from the wheel to the top of the hill, 
where it is connected with a long line of pumps, which extend to 
the bottom of the mine, for the purpose of lifting out the water 
which is constantly collecting there. The passing Tamar is thus 
made to do the work of the Devon Great Consols Mine, and its 
value can only be fully appreciated when, during dry summer 
seasons, the body of water passing through the river is so much 
diminished as not to give power sufficient for working the pumps. 
Then the big steam-engine, kept in readiness for such an eventuality, 
has to be set to work, and the consumption of tons of the ‘black 
diamond’ is required to replace the work of the absent water. In 
most mines in Devon and Cornwall, the smaller the rainfall, the 
smaller the coal bill; but here exactly the reverse—the greater the 
rainfall, the smaller the coal account. 
We need not go further than this mine to see abundant examples 
of the chemical utilities of water. The water pumped from the 
bottom of the mine is thrown, not to adit—/.e. to the nearest outlet 
above the water-shed of the neighbourhood, or the nearest valley— 
but is brought up to the highest ground on the mine. If we dip 
the blade of a knife into it we shall find that it will quickly become 
covered with copper. Every gallon of this water, or 70,000 grains, 
contains about 7 grains, or zg45p part, of copper. On bringing this 
water into contact with old iron, the sulphuric acid combines with 
the iron, for which it has a preference, converts it into the liquid 
form as sulphate of iron, and leaves the copper in the form of a 
metallic powder. The coppery water is distributed over the surface 
of old iron (placed in a circular tank) in fine showers, by the rotation 
of hollow perforated arms like the brewer’s aspersor used for mash- 
ing malt. The movement is effected by the gravitation of the 
water itself, so that the mechanical and chemical properties of the 
water are rendered available for the production of useful effects in 
the same apparatus. A portion of the iron is recovered from the 
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