![]() In essence, cold air cannot hold as much water vapour as warm air. Therefore air at 50% relative humidity, regardless of temperature, is holding half of its total possible water capacity. Put simply, the relative humidity is a measure of the percentage saturation of the air. Saturated air at 10 ☌ holds about 10 grams per cubic metre (g/m 3) of moisture at 20 ☌ about 17 g/m3 and at 30 ☌ more than 30 g/m 3. amount of water the air can hold at that temperatureĪir at 100 % relative humidity holds the maximum amount of water possible at that particular temperature and is said to be saturated. It is expressed as a percentage and can be defined as follows: RH = The relative humidity (RH) of the air is an indication of how much water vapour is in the air at a particular temperature compared with how much water vapour the air could actually hold at that temperature. But under unfavourable conditions, errors may amount to as much as ± 5% R.H., unless the corrections are used.These deterioration factors are considered together because of their close inter-relationship. teat papers can be estimated to about the nearest 1% R.H. The standards cover humidities above 50% R.H. Corrections are given for use when exposures other than 30 min. is sufficient except at very high humidities, where up to 2 hr. The influence of temperature and humidity on the time taken to reach colour equilibrium is described. Approximate corrections for temperature are given. Methods of impregnating the paper are described, also the above-mentioned method of preparing standards. A further improvement is the use of pure cotton tissue paper. Papers more suitable for use at high humidities have been prepared with cobalt thiocyanate solution. Alternatively, the addition of zinc chloride or certain other salts adapts the method for use at low humidities. The method can thus be adapted for accurate use at higher humidities. Certain salts, such as potassium thiocyanate and sodium thiosulphate, produce a similar, but much greater effect, and also produce stronger colours. Various colloid substrates other than paper, including mercerized cotton, cause the blue colour to persist at somewhat higher humidities possible uses of this are suggested. ![]() to the nearest 2% R.H., and above this range to the nearest 5%, except for low humidities at low temperatures. It is possible to measure humidities from 40 to 70% R.H. Colour standards for the matching of test papers are prepared by exposing papers over constant humidity solutions and then sealing them up in liquid paraffin between opal and clear glass. The time required for a piece of CoCl 2, paper to reach equilibrium with the atmosphere depends chiefly on humidity and temperature up to 2 hr. The paper is impregnated by dipping in a solution of CoCl 2.6H 2,O. It is shown that the colour is determined chiefly by the relative quantities of cobalt chloride and water in the paper. There is a close correspondence between colour and relative humidity, although the colour is influenced slightly by temperature. Cobalt chloride paper is blue at low and pale red at high humidities, with a series of lilac colours between. To meet the need for a simple method of measuring humidity in small spaces, a new method of using paper impregnated with cobaltous salts has been developed.
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