The boiler in the above case is negatively and the escaping "steam" is
positively charged. By changing the material of the linings of the jets,
or by adding turpentine the sign of the electricity is reversed. If the
water contains acid or salts no electricity is produced. The regular
hydro-electric machine is due to Sir William Armstrong.
Faraday obtained similar results with moist air currents.
Hydrogen.
An element existing under all except the most extreme artificial
conditions of pressure and cold as a gas. It is the lightest of known
substances. Atomic weight, 1; molecular weight, 2; equivalent, 1;
valency, 1; specific gravity, .0691-.0695. (Dumas & Boussingault.)
It is a dielectric of about the same resistance as air. Its specific
inductive capacity at atmospheric pressure is:
.9997 (Baltzman) .9998 (Ayrton)
Electro-chemical equivalent, .0105 milligram.
The above is usually taken as correct. Other values are as follows:
.010521 (Kohllrausch) .010415 (Mascart)
The electro-chemical equivalent of any element is obtained by
multiplying its equivalent by the electro-chemical equivalent of
hydrogen. The value .0105 has been used throughout this book.
Hygrometer.
An instrument for determining the moisture in the air. One form consists
of a pair of thermometers, one of which has its bulb wrapped in cloth
which is kept moist during the observation. The evaporation is more or
less rapid according to the dryness or moisture of the air, and as the
temperature varies with this evaporation the relative readings of the
two thermometers give the basis for calculating the hygrometric state of
the air. Another form determines the temperature at which dew is
deposited on a silver surface, whence the calculations are made.
Hysteresis, Magnetic.
A phenomenon of magnetization of iron. It may be attributed to a sort of
internal or molecular friction, causing energy to be absorbed when iron
is magnetized. Whenever therefore the polarity or direction of
magnetization of a mass of iron is rapidly changed a considerable
expenditure of energy is required. It is attributed to the work done in
bringing the molecules into the position of polarity.