Note on a simple form of Lippmann's capillary electrometer useful to physiologists / by Professor John G. M'Kendrick, M.D.

  • McKendrick, John G. (John Gray), 1841-1926.
Date:
[1883?]
Catalogue details

Licence: Public Domain Mark

Credit: Note on a simple form of Lippmann's capillary electrometer useful to physiologists / by Professor John G. M'Kendrick, M.D. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    a magnifying power of at least 300 to 400 diameters (No. 10 Hartnack). The other consists in cementing the sulphuric acid tube to the mercury tube, so that no evaporation takes place. By the first the instrument is rendered rciuch more sensitive; by the second, variations in the strength of the sulphuric acid which arise from evaparation are avoided.” The instrument thus described is difficult to make, and requires delicate handling. Whilst studying the subject, and endeavour- ing to see the phenomena for myself, I resorted to the simple expedient of taking a bit of glass tubing, 60 millimetres in length, and 2*5 millimetres in internal diameter, bending one end at a right angle, 20 millimetres from the end, and the other end at a right angle, 6 millimetres from the end, and then drawing out the tube to a capillary in the blow-pipe flame. The diameter of the capillary tube varies from *02 mm. to *001 mm. I then slip a bit of thick-walled india-rubber tube on one end of the glass tube, and exhaust the other end of the india-rubber tube with a powerful syringe. Having some clean mercury in a beaker covered with a deep layer of dilute sulphuric acid (1 to 20 of water by volume), I first immerse the end of the glass tube into the mercury, and then exhaust by the syringe. When mercury appears in the upper portion of the tube, I raise it a little so as to cause it to dip for an instant into the dilute acid, and then I dip into the mercury a second time and draw a little more of it into the tube. Thus, with a little practice, I succeeded in filling tubes, so that there is a reservoir of mercury at each end, with a little sulphuric acid in the centre of the capillary. This is placed on a suitable platform on the stage of the microscope, and a thin platinum wire is dipped into the mercury at each end. Such an instrument is very sensitive, showing the muscle- current, the negative variation, and the changes in potential in the injured heart of the frog whilst beating. As observed by Burdon Sanderson, it is striking to notice “ that the movements of the mercurial column not only correspond closely in time to the actual changes which they represent, but express with very great accuracy the differences of a potential which actually exist in each successive phase of a variation.” It will be found that, in the instrument I have described, the