Thermaesthesiometer.
An electro-therapeutic instrument for testing the sensitiveness of the
surface of the body to changes of temperature. Vessels of mercury are
provided with thermometers to indicate their temperature. One vessel is
surrounded by an electric conductor wound in a number of turns. The
temperature is raised by passing a current through this. By successive
applications of the vessels to the same spot upon the skin the power of
differentiating temperatures is determined.
Thermo Call.
(a) An electric alarm or call bell operated by thermo-electric currents.
It may serve as a fire alarm or heat indicator, always bearing in mind
the fact that differential heat is the requisite in a thermo-electric
couple.
(b) See Thermo-electric Call.
Thermo-chemical Battery.
A voltaic battery in which the electro-motive force is generated by
chemical action induced by heat.
The chemical used generally is sodium nitrate or potassium nitrate. The
positive plate is carbon. On heating the battery the nitrate attacks the
carbon, burning it and produces potential difference. For negative plate
some metal unattacked by the nitrate may be employed.
Fig. 330. POUILLET'S THERMO-ELECTRIC BATTERY.
Thermo-electric Battery or Pile.
A number of thermo-electric couples q. v., connected generally in
series.
In Nobili's pile the metals are bismuth and antimony; paper bands
covered with varnish are used to insulate where required. In Becquerel's
pile copper sulphide (artificial) and German silver, (90 copper, 10
nickel) are the two elements. The artificial copper sulphide is made
into slabs 4 inches long, 3/4 inch wide, and 1/2 inch thick (about).
Water is used to keep one set of junctions cool, and gas flames to heat
the other set. In Fig. 331, c, d represent the binding screws. The
couples are mounted on a vertical standard, with adjusting socket and
screw B, so that its lower end can be immersed in cold water, or raised
therefrom as desired.