On the penetrativeness of fluids / by J.K. Mitchell.

  • Mitchell, John Kearsley, 1793-1858.
Date:
1830
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Licence: Public Domain Mark

Credit: On the penetrativeness of fluids / by J.K. Mitchell. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    more slowly, the mixed gas returned, as indicated by the descent of the column of mercury. The retrogradation ceased only when the two columns came to equilibrium, or failing the possibility of that, when the mercury in the shorter limb had reached the membrane, through which mercury lias not been found able to penetrate. Acquainted with the fact, and the relative rate of the penetrative- ness of gases, the degree of force became the next subject of inquiry. That it was considerable, could be seen by looking at the stout mem- branes broken by it. By greatly increasing the length of the taller limb of an inverted syphon, similar to the one already described, I was able to bring to bear on the common air imprisoned in the shorter limb, a very con- siderable column of mercury. Up to a pressure of sixty-three inches of mercury, or rather more, equal to more than the power of two atmospheres, the penetrative action was found capable of conveying the gases, the subject of the experiment, into the short leg, through the gum elastic membrane. The entrance of the gas into the short leg, was expressed by the ascent of the long column of mercury in the other, which, as it entered, it was compelled to heave up. At the height of sixty-three inches, the membrane, though supported by cloth, could scarcely sustain the weight, and would not bear any in- crease of height. Although, therefore, at present, I do not know the limit of this power, I believe it will be found very much greater, because the power of the column which was tried did not, until a leak was sprung, seem to very sensibly affect the rate of en- trance. To the mind of a physician, the repetition of the foregoing experi- ments, substituting animal membranes for gum elastic would natur- ally suggest itself. Should animal membranes present the same phenomena, the interest of the investigation would be vastly enhanc- ed, and a very important service done to the cause of Physiological Medicine. That animal membranes would act in the same manner, was rendered probable by the well-known experiments of Priestley, who affected by means of oxygen the colour of blood confined in a bladder. It had also been observed by him that a closely tied blad- der, containing hydrogen gas is found after a considerable lapse of time, to contain only atmospheric air, and that, in quantity perhaps, equal to the hydrogen lost. Several other facts of the same kind are detailed by him. Finally, in the Journal of the Royal Institution, I find the following Notice of the Singular Inflation of a Bladder. By Thomas Graham, A. M. F. 11. S. E. Lecturer on Chemistry, Glasgow.