104. REGNAULT’S CONDENSER HYGROMETER
(Fig. 78) consists of a tube, C, made of silver, very thin, and perfectly polished; the tube is larger at one end than the other, the large part being 1·8 inches in depth, by 0·8 in diameter; this is fitted tightly to a brass stand, B, with a telescopic arrangement for adjusting when making an observation.
The tube, C, has a small lateral tubulure, to which is attached an India-rubber tube, with ivory mouth-piece; this tubulure enters C at right angles near the top, and traverses it to the bottom of the largest part.
A delicate thermometer, D, is inserted through a cork, or India-rubber washer, at the open end of the tube, C, the bulb of which descends to the centre of its largest part.
G is an attached thermometer for taking the temperature of the air, and F is a bottle containing ether.
To use the Condenser Hygrometer, a sufficient quantity of ether is poured into the silver tube to cover the thermometer bulb: on allowing air to pass bubble by bubble through the ether, by breathing in the tube, E, an uniform temperature will be obtained; if the ether continues to be agitated, by breathing briskly through the tube a rapid reduction of temperature will be the result; at the moment the ether is cooled down to the dew-point temperature, the external surface of that portion of the silver tube containing ether will become covered with a coating of moisture, and the degree shown by the thermometer at that instant will be the temperature of the dew-point.
This form of hygrometer, for ascertaining by direct observation the dew-point, is so superior to Daniell’s, both from its being more certain in its indications and economical in use, that Messrs. Negretti and Zambra have been induced to modify it, and reduce its price to little more than that of a good Daniell’s Hygrometer.
Fig. 79.
