Premium
The use of cobalt salts as indicators of humidity and moisture
Author(s) -
Solomon M. E.
Publication year - 1945
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1945.tb06763.x
Subject(s) - humidity , relative humidity , potassium thiocyanate , cobalt , moisture , chloride , cobalt chloride , materials science , chemistry , inorganic chemistry , composite material , meteorology , metallurgy , physics
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. Cobalt chloride paper is blue at low and pale red at high humidities, with a series of lilac colours between. There is a close correspondence between colour and relative humidity, although the colour is influenced slightly by temperature. It is shown that the colour is determined chiefly by the relative quantities of cobalt chloride and water in the paper. The paper is impregnated by dipping in a solution of CoCl 2 .6H 2 ,O. 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. exposure is allowed. 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. It is possible to measure humidities from 40 to 70% R.H. to the nearest 2% R.H., and above this range to the nearest 5%, except for low humidities at low temperatures. 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. Certain salts, such as potassium thiocyanate and sodium thiosulphate, produce a similar, but much greater effect, and also produce stronger colours. The method can thus be adapted for accurate use at higher humidities. Alternatively, the addition of zinc chloride or certain other salts adapts the method for use at low humidities. Papers more suitable for use at high humidities have been prepared with cobalt thiocyanate solution. A further improvement is the use of pure cotton tissue paper. Methods of impregnating the paper are described, also the above‐mentioned method of preparing standards. Approximate corrections for temperature are given. The influence of temperature and humidity on the time taken to reach colour equilibrium is described. An exposure of 30 min. is sufficient except at very high humidities, where up to 2 hr. may be necessary. Corrections are given for use when exposures other than 30 min. are allowed. The standards cover humidities above 50% R.H. at intervals of 5% R‐H.; teat papers can be estimated to about the nearest 1% R.H. But under unfavourable conditions, errors may amount to as much as ± 5% R.H., unless the corrections are used.