Eight ounces of pure Magnesia Alba were calcined with a strong fire in
an air furnace. Three hours calcination were necessary to discharge the
whole of the air from the Magnesia. When removed from the fire, it had
lost four ounces and three drachms of its original weight, and produced
no effervescence with acids; it had not acquired any degree of acrimony
to the taste, and when thirty grains of it were diluted with a few
spoonfuls of water and swallowed, it occasioned no uneasy sensation in
my stomach, nor sense of heat in my throat; proved nearly as aperient
as a double quantity of uncalcined Magnesia, and operated without the
least griping. It was remarkable that calcination had not reduced the
powder in bulk, in proportion to the diminution of its weight.
By the process of this experiment, Magnesia Alba is not only divested
of the disagreeable qualities which have been alluded to, but acquires
new properties which render it likely to answer some very important
practical purposes.
Doctor Macbride, who has with the greatest ingenuity and accuracy,
prosecuted the investigation of the nature of fixed air, discovered,
that a large quantity of it is discharged in the fermentation of
alimentary mixtures; and that the saliva being, in a healthy state,
void of air, acts as an absorbent of it, thereby moderating and
restraining the discharge of this vapour in the stomach. But when the
tone of that viscus is too relaxed to perform the digestion of the
aliment with proper vigour, or the saliva is diseased and corrupted,
the air expelled from the food becomes too elastic, and produces those
disorders which are commonly termed flatulent; and, perhaps, by its
effects on that prodigious plexus of nerves which is diffused over the
coats of the stomach, may sometimes occasion spasmodic or paralytic
affections.
It has been observed above, that calcareous earths, alkaline salts, and
Magnesia, being deprived of their air, attract it from every substance
with which it has a smaller degree of affinity. The two former becoming
highly caustic by the loss of their air cannot be administered but in
very small doses. But the calcined Magnesia being absolutely divested
of air, though not rendered acrimonious, and being able to absorb a
large quantity of this elastic flatus, may act more powerfully than
the whole tribe of carminatives, yet essentially differs from them in
many respects. _They_ contain a large quantity of air; _Magnesia_
in this state is entirely free from it; _Aromatics_ may be apt to
ferment, and increase acidities; the _calcined Magnesia_ is incapable
of effervescence, and powerfully corrects an acescent disposition in
the gastric juices; the _former_ constipate the belly; the _latter_ is
laxative.
From this property of Magnesia, when calcined, of absorbing air,
it occurred to me, that it would of all others be the most proper
cathartic for patients labouring under the stone, who might be taking
the lixivium saponarium, having the advantage over all the vegetable
purgatives, which abound with air, and consequently have a tendency
to render the caustic alkali mild and inert. I even flattered myself
that it might coincide in promoting the efficacy of that powerful
solvent of the human calculus. Dr. Macbride's theory, that the lixivium
acts by depriving the calculus of its fixed air, appears to be well
founded; and Mr. Chittick in the exhibition of his nostrum, which,
notwithstanding all his empirical arts to disguise it, is now known
to have been the soap ley, kept his patients from every kind of diet
abounding with air. We may therefore venture to recommend it, though
not as a lithontriptic, being insoluble in water, yet as an assistant
to the lixivium, by absorbing a part of that air in the primæ viæ which
would otherwise be attracted by the caustic alkali, and thereby render
it incapable of acting on the calculus.
In all the diseases attended with an acescent disposition in the first
passages, in which Magnesia has been recommended in the third chapter,
the calcined powder may be given with superiour advantages, as it will
not produce any of those inconveniences, which have been attributed to
that medicine when uncalcined. Besides that it will act in a three-fold
capacity, viz. as an absorbent of air, and of acidity, and also as an
easy purgative. I know several persons who could never bear to take
the common Magnesia, with whom the calcined perfectly agrees. It seems
likely to be very serviceable in flatulent cholics, and I have been
informed of one very obstinate chronical case of that kind, which
was greatly relieved, though not perfectly cured by the use of it in
the Chester Infirmary, under the direction of a very judicious and
ingenious physician.
Even in gouty habits, joined with some warm aromatic, it may probably
be found useful in correcting the very great flatulency which so much
afflicts persons of this constitution; and perhaps the Cayenne pepper
would be the most proper addition to it, on account of the small
quantity of this spice that would be necessary to make the Magnesia
gratefully warm to the stomach.
It will appear in the succeeding chapter that calcined Magnesia is
strongly antiseptic: but I shall postpone my observations on that
subject till I have related the experiments which prove its claim to
that property.