The first and most essential constituent of food is water. Three fourths
of the body is composed of water, and it is by the agency of water that
all kinds of food are taken up into the system. Solid food contains
large proportions of water, but, in proportion to the dryness of food,
water should be added to it, in the form of some kind of beverage.
QUANTITIES OF WATER IN 100 POUNDS OF DIFFERENT
KINDS OF SOLID FOOD.
_Vegetable Food_.
lbs. lbs.
Cabbage 92 Maize 14
Turnips 87 Peas 14
Carrots 86 Beans 14
Beetroot 83 Lentils 14
Parsnips 79 Buckwheat 14
Potatoes 75 Oatmeal 13
Bread 44 Rye 13
Flour 14 Rice 13
Barley Meal 14 Cocoa 5
_Animal Food_.
Milk 86 Lamb 50
Eggs 80 Mutton 44
Fish 78 Cheese 40
Veal 62 Pork 38
Beef 50 Bacon 30
_An imperial gallon of water weighs_ 10 _pounds avoirdupois weight_.
Water for dietetical purposes is obtained principally from three
sources:—1. Rivers; 2. Surface wells; 3. Deep or Artesian wells. Water
from all three sources contains saline or mineral matters in solution,
and, provided they are not in quantities so large as to act injuriously
on the system, water may become a source of supply of these constituents
to the body. The best remedy for impure water is filtering, which may be
done by passing the water through charcoal and sand. “A Poor Man’s
Filter” is exhibited in the Museum, which can be very easily and cheaply
constructed by using a common flower-pot, glazed inside, plugging the
drainage hole (not too tightly) with a piece of clean sponge, then adding
layers of animal charcoal, sand, and rather coarse gravel. Filters from
the establishments of the Messrs. Lipscombe, the Messrs. Ransome, and the
Carbon Filter Company are also exhibited. The passing water over iron
has been found to have a remarkably purifying effect, and this has been
patented by Dr. Medlock.
The _organic_ impurities of water are best tested by the aid of the
microscope, but, as an examination by this instrument requires much time,
a ready method of obtaining a knowledge of the comparative organic
impurity of waters is the addition of the permanganate of soda or potash.
This salt, which gives to water a beautiful red colour, is easily
decomposed by organic matters. When the same quantity of the
permanganate is added to a series of waters containing organic matters,
those which contain the least retain the most colour and _vice versâ_.
Waters thus tested are exhibited in the Collection.
Water from the chalk or limestone is generally hard, arising from its
holding in solution carbonate of lime, which, although insoluble in
water, is dissolved by the agency of carbonic acid. By Clark’s softening
process the carbonic acid is neutralized by lime, and the carbonate of
lime is thus thrown down. Specimens are exhibited.
Water is frequently stored in leaden cisterns, and when free from
carbonic and phosphoric acids it acts powerfully on lead. Thus distilled
water becomes speedily tainted with lead, whilst Thames water and London
surface well water act but slightly upon it. Specimens of these waters
acting upon lead are exhibited in the Collection.