Patent GB-559741-A (GB)
Title: Improvements in or relating to apparatus for testing gas
IPC: G01N27/416
Filed: 1942-02-07
Abstract: 559,741. Determining physical qualities. MINE SAFETY APPLIANCES CO. Feb. 7, 1942, No. 1641. Convention date, Feb. 18, 1941. [Class 37] In an arrangement for testing gas for a particular constituent, and of the general character set out in Specification 505,628, in order to enable the apparatus to be used for continuous as opposed to intermittent testing, the relatively-large exposed surface of active electrode is replaced by an arrangement in which the surface exposed is relatively small and in which the electrolyte is kept circulating. Means is also provided for independently adjusting the sensitivity and zero reading of the system. Gas is introduced into a gastight cell C containing an electrolyte maintained at constant level and divided by a partition 13 into two inter-communicating compartments. The gas inlet leads into an electrode compartment, passes into the other compartment, and out through a port 10. One electrode comprises, for example, a copper rod 43 shrouded with insulation 44 and connected to a terminal 46. The active electrode comprises a disc 15, also of copper, having both faces covered by inert material, as by moulding the disc in rubber. A central metal bushing 17 is fixed to a rotatable insulation-sheathed shaft, the insulation 20 being enlarged to provide a backing for one facing of the disc, whereas a cap 24 threaded on the shaftend comprises a similar backing 23 for the other face of the disc. The part of the disc 15 that is exposed to the gas thus forms a reaction product which is subsequently removed in the electrolyte, as in the prior Specification, the resulting e.m.f being a measure of the concentration of constituent. A bronze bearing 30, Fig. 5, is clamped by plate 33 in a metal bushing 28 assembled with a gasket 29 in the cell-cover. A felt sealing washer 31 and a smooth hard gasket 32 are also provided. The bushing 28 carries a brush holder 36 carrying a metal cylinder 37 carrying brushes 38 rubbing on a stainless steel contact on the shaft 20, a metal cap 40 and felt washer 41 being also provided. In order to maintain the electrolyte at the right strength and sensitivity it is withdrawn from the cell C at the outlet 7, Fig. 6, is passed through a copper voltameter 88 in order to remove copper from the solution, and into a storage tank 8a from which it is pumped back into inlet 6. The outlet 7 is arranged to maintain a constant level of liquid in the cell and is provided with an anticapillarity weir and with a fitting 702 having a transparent case 705 for viewing the operation, Fig. 2 (not shown). Fig. 7 shows an arrangement for checking the sensitivity by means of adjustable rheostats 53, 56, 57 in a resistance-net fed by battery 64, and including the cell C and an instrument 52 calibrated to read the per cent concentration directly. By flushing the cell with a known concentration, the instrument-reading for that concentration can be checked and rheostat 57 adjusted if necessary. By flushing with a gas free of the known constituent, the zero reading can be altered by rheostats 53, 56 for fine and coarse adjustment, respectively. Such checking can be effected at regular intervals by a clock operating a switch and two-way valve. In the determination of oxygen in other gases, the electrolytes referred to in Specification 505,628 may be employed. In Fig. 6, such gas is put in at pipe 67, passed through a scrubber 68 for removing carbon dioxide, through pipes and valves to a carbon-dioxide indicator 80, or if deemed necessary, a further carbon-dioxide absorber 94, thence to a filter 82, flow-regulator 83, and flow-meter 84 to the cell. The supply of oxygen of known concentration is indicated at 82.