Frequent objections have been made to the use of Magnesia Alba, on
account of the great quantity of air which enters into its composition.
Whenever it meets with an acid in the stomach they immediately unite;
but in forming this union, all the air contained in the Magnesia
is discharged with a great degree of effervescence, and recovering
its elasticity sometimes occasions very uneasy sensations in weak
bowels,[q] inflating and distending them overmuch, inducing griping
pains, and above all a sense of debility or sinking, which is not
easily described.
[q] Neque tamen præterire possumus, id incommodi nos quandoque ab hoc
Magnesiæ pulvere deprehendisse, quod flatulentias et morsicationes
in imo ventri reliquerit, si videlicet frequentius in usum trahatur,
primaque regio progignendis corrosivis succis, ut in hypochondriacis
fieri solet, exposita sit.
Hoffman. Oper. Tom. 4. p. 381.
My much respected friend Doctor Percival, who had often complained of
these disagreeable effects from the use of Magnesia, suggested to me
the idea of depriving it of its fixed air by calcination, having been
informed that they would be obviated by this method. Doctor Black
had indeed proved the practicability of the process, but he does not
appear to have made trial of the calcined Magnesia as a medicine.
In consequence of the above hint I calcined some Magnesia, and was
afterwards insensibly led to make further experiments, the event of
which, I hope, will be deemed of sufficient importance to apologize for
my communicating them to the public.