| 摘要 |
<p>An indicating device comprises a capillary material impregnated with one or more reagents, sealed between two films of synthetic resin at least one of which is transparent, the device having or being adapted in use to have, at least one edge of the capillary material free of synthetic resin. In a specific embodiment the device is made completely sealed by resin or as a continuous strip, the device being prepared for use by cutting to the required size and exposing the capillary material. The device may have an aperture for venting either at the same or the opposite end to the free capillary edge. Two strips of capillary material may be incorporated side by side but spaced apart by a plastics film. The capillary material may be paper, cellulosic, acrylic, synthetic or glass fibres or particulate material, cellular materials are also suitable. The synthetic film may be polyethylene, polypropylene, PVC, polyvinyl acetate, polyvinylidene chloride but a composite sheet of polyterephthalate and polyethylene is preferred. Pressure-sensitive adhesives may be used to join the capillary material and the film. If paperboard is used then it is given a plastics coating to render it impervious. The reagents may be fixed or movably disposed in the capillary material. Various applications of the indicator device are given, amongst which are (a) determination of solute:solvent ratio in a solution according to rate of travel of both components in the capillary material, a material impregnated with methyl red or pehnolphthalein being used for acid or alkali concentrations or impregnated with AgNO3 and dichlorofluoescein to determine salt concentration (b) determination of acid strength using ion-exchange paper impregnated with an indicator (c) measurement of water vapour in air by using a material impregnated with a hydroscopic material e.g. LiCl or CaCl2 and Karl Fischer Reagent wherein a predetermined volume of air is drawn up through the capillary material (d) analysis of freshness of milk using paper impregnated with methyl red and an ion-exchange resin.</p> |
