A Treatise on Adulterations of Food, and Culinary Poisons | Page 8

earthy salts.
Green esculent vegetable substances are more tender when boiled in
soft water than in hard water; although hard water imparts to them a
better colour. The effects of hard and soft water may be easily shown in
the following manner.
EXPERIMENT.
Let two separate portions of tea-leaves be macerated, by precisely the
same processes, in circumstances all alike, in similar and separate
vessels, the one containing hard and the other soft water, either hot or
cold, the infusion made with the soft water will have by far the
strongest taste, although it possesses less colour than the infusion made
with the hard water. It will strike a more intense black with a solution
of sulphate of iron, and afford a more abundant precipitate, with a
solution of animal jelly, which at once shews that soft water has
extracted more tanning matter, and more gallic acid, from the
tea-leaves, than could be obtained from them under like circumstances
by means of hard water.

Many animals which are accustomed to drink soft water, refuse hard
water. Horses in particular prefer the former. Pigeons refuse hard water
when they have been accustomed to soft water.
CHARACTERS OF GOOD WATER.
A good criterion of the purity of water fit for domestic purposes, is its
softness. This quality is at once obvious by the touch, if we only wash
our hands in it with soap. Good water should be beautifully transparent;
a slight opacity indicates extraneous matter. To judge of the perfect
transparency of water, a quantity of it should be put into a deep glass
vessel, the larger the better, so that we can look down perpendicularly
into a considerable mass of the fluid; we may then readily discover the
slightest degree of muddiness much better than if the water be viewed
through the glass placed between the eye and the light. It should be
perfectly colourless, devoid of odour, and its taste soft and agreeable. It
should send out air-bubbles when poured from one vessel into another;
it should boil pulse soft, and form with soap an uniform opaline fluid,
which does not separate after standing for several hours.
It is to the presence of common air and carbonic acid gas that common
water owes its taste, and many of the good effects which it produces on
animals and vegetables. Spring water, which contains more air, has a
more lively taste than river water.
Hence the insipid or vapid taste of newly boiled water, from which
these gases are expelled: fish cannot live in water deprived of those
elastic fluids.
100 cubic inches of the New River water, with which part of this
metropolis is supplied, contains 2,25 of carbonic acid, and 1,25 of
common air. The water of the river Thames contains rather a larger
quantity of common air, and a smaller portion of carbonic acid.
If water not fully saturated with common air be agitated with this
elastic fluid, a portion of the air is absorbed; but the two chief
constituent gases of the atmosphere, the oxygen and nitrogen, are not
equally affected, the former being absorbed in preference to the latter.

According to Mr. Dalton, in agitating water with atmospheric air,
consisting of 79 of nitrogen, and 21 of oxygen, the water absorbs 1/64
of 79/100 nitrogen gas = 1,234, and 1/27 of 21/100 oxygen gas = 778,
amounting in all to 2,012.
Water is freed from foreign matter by distillation: and for any chemical
process in which accuracy is requisite, distilled water must be used.
Hard waters may, in general, be cured in part, by dropping into them a
solution of sub-carbonate of potash; or, if the hardness be owing only
to the presence of super-carbonate of lime, mere boiling will greatly
remedy the defect; part of the carbonic acid flies off, and a neutral
carbonate of lime falls down to the bottom; it may then be used for
washing, scarcely curdling soap. But if the hardness be owing in part to
sulphate of lime, boiling does not soften it at all.
When spring water is used for washing, it is advantageous to leave it
for some time exposed to the open air in a reservoir with a large surface.
Part of the carbonic acid becomes thus dissipated, and part of the
carbonate of lime falls to the bottom. Mr. Dalton[11] has observed that
the more any spring is drawn from, the softer the water becomes.
CHEMICAL CONSTITUTION OF THE WATERS USED IN
DOMESTIC ECONOMY AND THE ARTS.
Rain Water,
Collected with every precaution as it descends from the clouds, and at a
distance from large towns, or any other object capable of impregnating
the atmosphere with foreign matters, approaches more nearly to a state
of purity than perhaps any other natural water. Even collected under
these circumstances, however,