hygrometer

(hi-grom’e-tér), n. [ wet, moist, + érpov, a measure. ] An instrument A for measuring the amount of the moisture of the agarics, atmosphere, or more accurately for deter min habit, ing the hygrometrie state or relative humidity, and which is the ratio between the actual amount the however, of water-vapor present in the air and that reple, quired in order to saturate it completely. A comhygroplasma mon form is the Daniell hygrometer, which consists of vypoc, a bent gla tube terminating in two In bulbs, one coypart ered with muslin, hygroscope the other of black gla and contain wet, ing ether and at her or mometer. Ether of being dropped on approximately the muslin of the upper bulb, the vaattempting por within is connoted densed,and the con- (also sequent eva por a which tion of the ether expands from the other bulb ing cools the air about is it, and finally to graduated such a degree that ing-screw moisture is deposit whenever ed upon its black to surface. The drop on ping is now sus hygroscopic pended, and the a. temperature is taining taken from the in- Daniell Hygrometer. closed thermome- A, bulb containing ether; 4, evaporation ceptible ter; the mean bebulb covered with muslin. tected tween this temper- —2, ature and that observed when the moisture disappears is the dew-point. ‘The hygrometric state is the ratio be absorbing tween the pre ure of water-vapor corresponding res pec atmosphere, tively to the dew-point and to the temperature of the air sue, at the time as given by the thermometer on the stand. a This form is called a dew-point or condensing hygrometer. Instead of a black gla bulb, a silver ve el is sometimes used, as in Regnault’s hygrometer. In the chemical be, hygrometer a known volume of air is pa ed over some moisture. hygroscopic substance, as calcium chlorid, contained in a the drying-tube. This absorbs the aqueous vapor, and by its vealed increase in weight gives the means of calculating the substances amount present in the unit of volume. The wet-bulb moisture, thermometer, or psychrometer (see psychrometer), also gives be a simple method of obtaining the hygrometric state, by means of appropriately constructed tables. 3.