Aniline vapour / Department of Scientific and Industrial Research.

Date:
1939
Catalogue details

Licence: Public Domain Mark

Credit: Aniline vapour / Department of Scientific and Industrial Research. Source: Wellcome Collection.

    13/20 (page 7)
    It is possible that slight variations may occur in the intensity of the colour given by different batches of the Tolui- dine Blue stain. A new supply of the latter should therefore be tested before use as follows :— The dyestuff is finely ground and thoroughly mixed, and a representative sample used to make up a 0-028 per cent solution as described above; the standard colour No. 3 is then prepared from this solution. The following solution is then made up: 30 g. copper sulphate (CuSO, 5H,O) of Reagent quality are dissolved in distilled water and the volume made up to 100 ml. To this is added 1-2 ml. of a freshly prepared solution made by dissolving 0-3 g. of potassium permanganate of Reagent quality in 100 ml. of distilled water, and the solutions are thoroughly mixed. The coloured solution thus obtained is then immediately compared with the standard No. 3 prepared from the dyestuffs, the two solutions being observed side by side in small tubes of equal bore. The depth of colour in the two tubes should be identical; if any difference is observed, the strength of the original 0-028 per cent Toluidine Blue stock solution is ad- justed until an exact match is obtained with the new standard No. 3 prepared from it. The standard colours for use in the test can then be prepared from this modified 0-028 per cent stock solution as described above. Method Before carrying out any test, the valves of the hand pump shall be tested (with the bubbler disconnected) by closing the inlet with the finger, and drawing out the piston slowly to its full extent. On releasing the piston, it should rapidly return to its original position. The washer on the pump piston may shrink in the course of time. (This trouble is easily remedied by soaking the piston in warm liquid paraffin for a few hours.) To prepare for a test, 10 ml. of the hydrochloric acid are measured into the side-arm test tube, and the latter connected up with the pump as described above. To obtain a preliminary indication of the atmosphere to be tested, five strokes of the pump shall be made very slowly and steadily (approximately 10 seconds per stroke). Five strokes is convenient for a preliminary test. The complete test takes about half an hour, but the bulk of the colour develops in the first 10 minutes. Concentrations up to 1 part in 15,000 can thus be roughly estimated in +-hour by using 5 strokes. Further,