A sensitive method for observing changes of electrical conductivity in single hygroscopic fibres

Abstract

Some years ago, after noticing that an inconstant and excessive leak from the insulated system of an electroscope was due to a barely visible filament of spider’s web, the author was struck by the beautiful way in which the arrangement responded to changing atmospheric conditions. An attempt to adapt this observation to the study of the absorption of moisture by fibrous substances has led to the method described in this paper. Our expectations as to its possibilities have been more than realised. The effect of changes in atmospheric conditions upon the state of fibrous substances, as indicated by their electrical conduction, can be followed continuously. The conductivity time curves, shown in figs..3a, 3b, 5a and 5b, where the actual experimental values are plotted, are typical examples of the accuracy obtainable. Bulk methods of measuring the conductivity of hygroscopic fibrous substances have always given complex results. By examining microscopic amounts, such as single cotton hairs 1 cm. long, we are able to reduce errors incurred by ( a ) imperfect contact, ( b ) pockets of moisture trapped in the interstices of the fibrous mass, ( c ) difficulties of conditioning large quantities of material under compression as a consequence of restriction of air movement ( d ) displacement (under pressure) of absorbed moisture from the materials whose structures are, in effect, like that of a sponge.