Into one phial were put two scruples of Magnesia, into a second the
same weight of calcined Magnesia, and into three others the same
quantity of chalk, _pulv. e chel. cancr. comp._ and _pulv. contrayerv.
comp._ To each of these, two drachms of fresh beef, and two ounces of
distilled water were added. A sixth phial was kept as a standard, and
contained only the same proportions of beef and water. The bottles,
distinguished in the order they are mentioned by the numbers 1, 2, 3,
4, 5, and 6, were placed in the same heat as that to which the Magnesia
was exposed in the former experiment, and were frequently shaken up and
examined.
In twelve hours, number 1 began to smell; an intestine motion was
perceptible in numbers 3, 4, 5, and 6, but especially in the chalk. In
twenty-four hours, number 1 was become highly putrid, number 3 smelled
offensively, number 4 had acquired a very slight foetor, as had
number 5 which fermented briskly. The standard had acquired a vinous
smell, but number 2 remained unchanged.
In thirty six hours, number 3 was very putrid, numbers 4 and 5 had
made little progress since the last examination, though number 5
was rather more putrid than the other, allowance being made for the
peculiar odour of the contrayerva; but in four hours more they both
stunk intolerably. The standard continued two or three days longer
before it became absolutely putrid, and the calcined Magnesia preserved
the beef untainted for several days longer, when it was removed to make
room for other phials. The water which was mixed with the calcined
Magnesia differed from all the others in not becoming bloody, nor did
the beef in it seem so tender as when infused in lime water.
When I made the first experiment, I had not observed any discharge of
air from the Magnesia and beef, and in the present one no fermentation
was perceptible either in number 1 or 2. As this was an unexpected
circumstance in the former, I repeated the experiment several times,
but the event was always the same.
Magnesia was afterwards compared with crab's eyes, burnt hartshorn, and
prepared coral. The mixture with Magnesia grew putrid first, afterwards
that with the crab's eyes; the other two remained for some hours longer
before the putrid foetor came on.
From the above experiments it appears that Magnesia Alba, when replete
with fixed air, is a stronger septic to animal flesh than any other
absorbent which was compared with it; and yet when deprived of its air
by calcination, it powerfully resists putrefaction. Dr. Macbride has
endeavoured to account for this difference between calcareous earths
and quick-lime, by supposing the particles of the lime to insinuate
themselves intimately into the texture of the beef, and to prevent
the escape of the fixed air, by attracting, absorbing, and thus
confining it within the substance of the beef. How far this theory
is satisfactory is not my province to determine; and the matter is
so obscure, that I do not presume to offer any conjecture of my own,
relative to the reason of it.
Nitre is found to be a strong antiseptic when applied to animal flesh,
but to resist the putrefaction of bile with a very disproportionate
force: and Dr. Percival has lately observed the same difference in
the action of the Columbo root. These variations encouraged me to
try the effect of Magnesia on gall; but being strongly prepossessed
with the notion of its septic quality, I entertained very small hopes
of a different event. I was also desirous to compare the action of
the calcined Magnesia with the other. The heat used in the succeeding
experiments was the same as that in the preceding trials.