Hermann's phenomenon / by G.S. Walpole.

  • Walpole, George Stanley.
Date:
[1914?]
Catalogue details

Licence: In copyright

Credit: Hermann's phenomenon / by G.S. Walpole. Source: Wellcome Collection.

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    glass tube fitted with an open stopcock. These stopcocks are marked c and cl. All three small taps c, d, and e, are now closed, and from the anode and cathode limbs as much fluid withdrawn by means of a suitable pipetting arrangement as is possible without allowing air to run back into C or D. When this is done, a spiral silver sheet anode connected by a silver wire to the positive binding screw is introduced into the anode limb, and normal sodium chloride run in slowly until its meniscus reaches a certain mark. This mark is so arranged that when air is let in through c the column in 0 does not move, for it balances that in the anode limb exactly. In a similar fashion the cathode limb is filled with 5-per-cent, copper chloride solution round a copper electrode. The stopcocks c, d, and c, are now opened and the rubber stoppers carefully removed. The large taps are opened with a slow even motion and e is shut. The result is that the four fluids are arranged as it was desired with four sharp boundaries in the positions indicated in the sectional drawing. The position of the “ middle tube fluid ” and the “ electrode fluid ” are shown by stippling. The “side tube ” space is left clear. It should be noticed that the position of the apparatus in its wooden frame has been carefully adjusted so that the tops of the plugs of the large taps are in the same horizontal plane. The adjustment is checked by filling M and the bores of both taps with a coloured fluid and noting the position of the two meniscuses relative to the plugs of the taps. The two binding screws are now put in connection with a direct lighting main, say, at 115 volts. It is, of course, one essential condition of these experiments that the actual current passed be so small that even at this voltage the rise of temperature due to the heat generated in the apparatus is insufficient to cause any appreciable convection currents. x4fter disconnecting again from the main the large taps are turned off very slowly to prevent mixing of the solutions by eddy currents, and the distribution of acid and alkali at the boundaries is investigated by one or other of the various simple devices which suggest themselves at once. A “ medicine dropper ” made of hard glass and drawn out to a long fine capillary is convenient for introducing strong indicator solution at the desired point, for removing liquid from a given region, or for mixing small quantities of fluid by drawing them up successively and delivering them into a common vessel after the manner of the bacteriologist. If, for example, in an experiment where the “middle fluid” is 5-per-cent, sodium chloride and the “side tube fluid 0'05-per-cent, sodium chloride, azolitmin dissolved in 0'05-per-cent, sodium chloride be floated upon the meniscus of A and B, it will in a few minutes diffuse and fall down to the four boundaries and demonstrate that, though the liquid in between has
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