GB405598A - Method of determining the concentration of mixtures of substances - Google Patents

Abstract

The concentration of one component in a mixture is determined by measuring the difference in the specific inductive capacities of a pure solvent and the solution obtained by extracting the component to be measured with that solvent. Preferably the apparatus used comprises two oscillating circuits, each containing identical measuring condensers capable of being filled with a gas or liquid, which are adjusted to oscillate at the same frequency when the condensers are filled with the same substance. The condensers are then filled with the solvent and solution respectively and the resulting frequency difference measured, e.g. by an arrangement similar to that used in superheterodyne wireless receiving circuits, by thermo-elements, by galvanometers with rectifiers, alternating current voltmeters, &c. The heterodyne effect may also be amplified and employed to actuate relays, e.g. to operate recording devices, acoustic or optical signalling apparatus or automatic regulating devices. For exact measurements, the condensers are kept at constant temperature. If the conductivity of the substances affects the accuracy of the capacity variations, conductivity measurements may be made by using the condensers as conductivity cells, disconnected from the oscillating circuits, the two condensers and two oscillating circuits forming the arms of a Wheatstone bridge. According to examples (1) purity tests for distilling fractions are carried out by adjusting the oscillators to the same frequency when the condensers are empty. One condenser is filled with the pure liquid desired, and the distillate arranged to flow through the second condenser. When the pure substance distils over, the frequency difference is zero. (2). The variation of s.i.c. with concentration is determined empirically and the results used to determine absorption equilibria, one condenser being filled with solvent and the other with the mixture which has been treated with absorbent. Rates of diffusion or solution and the degree of saturation may be similarly determined. Also the determination of the fatty contents of liquid and solid substances, analysis of sewages, &c. may be carried out by a similar method. (4) The moisture content of decomposable substances or bodies having a large surface area, e.g., grain, meal products, wood, mortar, tobacco, explosives, &c. may be measured by extracting the water by means of dioxane and comparing its s.i.c. with that of the pure solvent. (5). The concentration of one component of a gas mixture such as an inflammable or noxious gas may be measured by comparing the untreated gas with the mixture after treatment with a suitable adsorbent or reagent to remove the required component.