Section 25 in The West Bengal Factories Rules, 1958
25. Specification of hygrometer.
(1)Each hygrometer shall comprise two mercurial thermometer of wet bulb and dry bulb of similar construction, and equal in dimension, scale and divisions of scale.They shall be mounted on a frame with a suitable reservoir containing water.(2)The wet bulb shall be closely covered with a single layer of muslin, kept wet by means of a wick attached to it and dipping into the water in the reservoir. The muslin covering and the wick shall be suitable for the purpose, clean and free from size or grease(3)No part of the wet bulb shall be within 7.6 centimetre of the dry bulb or less than 2.5 centimetres from the surface of the water in the reservoir and the water reservoir shall be below it, on the side of it away from the dry bulb.(4)The bulb shall be spherical and of suitable dimensions and shall be freely exposed on all sides to the air of the room.(5)The bores of the stems shall be such that the position of the top of the mercury column shall be readily distinguishable at a distance of 60 Centimetres.(6)Each thermometer shall be graduated so that accurate readings may be taken between 10 and 50 degrees [in the centigrade scale.] [Inserted by W. B. Factories (Amendment) Rules, 1991, dated 27.11.1991](7)Every degree from 10 degrees up to 50 degrees shall be clearly marked by horizontal lines on the stem, each fifth and tenth degrees shall be marked by longer marks than the intermediate degrees and the temperature marked opposite each tenth degree, i.e., 10, 20, 30, 40 and 50.(8)The markings as above shall be accurate, that is to say, at no temperature between 10 and 50 degrees shall the indicated readings be in error by more than two-tenths of a degree.(9)A distinctive number shall be indelibly marked upon the thermometer.(10)The accuracy of each thermometer shall be certified by the [* * * *] [Omitted vide Notification No. 340 L.W./L.W./L.W./IR-4/85 dated 2nd April, 1986] National Instruments Factory, Calcutta, or some competent authority appointed by the Chief Inspector and such certificate shall be attached to the Humidity Register.
