Device for measuring the refractive index of a fluid, in particular intended for measuring the density of that fluid or the concentration of a substance dissolved in that fluid.

摘要

In order to measure the refractive index of a fluid use is made of a rod (1) which projects into the fluid and has a refractive index which is slightly larger than that of the fluid. At the end which is not immersed in the fluid, the rod is provided with a light source (3) radiating into the rod and with a light detector (5). That part of the rod which is to be immersed in the fluid is partially surrounded by a casing which permits only total reflection of the light, while at the site of the part or parts of the rod not surrounded by the casing refracted light can, depending on the refractive index of the fluid, leak into the fluid. A casing which is stable against the corrosive action of an agressive fluid, such as concentrated sulphuric acid in a battery, consists, according to the invention, of a layer (10), trapped in a transparent tube (8), of a medium which has a lower refractive index than the said rod, in particular gas or vacuum. In order to nullify the interfering action of hydrogen gas bubbles adhering to the rod, at least that part of the rod, projecting into the fluid, which is not surrounded by the casing can project into a holder (12). which, below the rod, is provided with openings (13), a line (14) for supplying gas under pressure opening into the upper part of the holder.