200 JCURNAL OF THE PLYMOUTH INSTITUTION. 
‘water by so exposing the solution of the iron, after the copper has 
been precipitated, as by the oxidizing action of the air to mineralize 
it in the form of a persulphate, which by drying is eventually 
obtained in the form either of a yellowish brown ochre, or, by fur- 
ther exposure to heat and calcination, a rich purple or reddish-brown 
colcothar, or crocus, or peroxide of iron. 
We cannot afford time for more than a mere enumeration of some 
of the uses of water in the economy of a town such as Plymouth ; 
such, for example, as for the production of power, either directly 
by water-wheels or turbines, or indirectly for the steam-engine. In 
passing through the town we find engines at work sawing timber, 
grinding corn, making flour, baking bread, printing newspapers, 
manufacturing sugar, starch, oils, paints, colours, rolling lead, ham- 
mering iron, breaking stones (turning stones into bread), spinning, 
weaving, washing, dyeing, making soap, loading ships, unloading 
them, bringing into the town and taking away men and things ; 
and so familar are water-engines becoming now that we cannot 
have the comfortable finishing touch to a hair-dressing and head- 
ache-dispelling without the aid of the little turbine-driven circular 
brush. We have, moreover, water to drink in all its varied forms 
of tea, coffee, beer, cider, wine, &.; water to eat in every form of ~ 
food, especially of bread, the staff of life. We want water for 
cleansing person and raiment, house and furniture. 
It is not until the supply is partially cut off that we even begin 
to appreciate the value of this substance. Although comparatively 
a fair-supply of water is obtained in this town, yet the increased 
consumption is now pressing for serious consideration of the best 
means of improved supply. Our Dartmoor hills present peculiar 
facilities for obtaining this supply. There are localities amongst 
the hills where the waters that so abundantly fall on them may be 
stored up in artificial lakes in any quantity, whence supplies may 
be led off as they may be required, instead of its being allowed to 
run away as it falls in its course, frequently causing injury and 
destruction to property. Since the recent great advance in the 
price of coal, the importance of water as a source of power has 
greatly increased. 
One of the principal mineral resources of the two counties is 
china clay. In 1872 the quantities of china clay raised in Cornwall 
in 106 different china clay works amounted to 141,000 tons; and 
in Devonshire, from nine different works, to 26,982 tons. Mere 
