Thus lime being deprived of its air by calcination, and having a stronger affinity with it than alkaline salts have, being mixed with a lixivium of these salts, absorbs all the air from them, deprives them of their property of effervescing with acids, and renders them more acrid, at the same time that the lime becomes mild, and incapable of impregnating water, but recovers its power of fermenting when mixed with an acid.
CHAP. V.
On the medicinal virtues of CALCINED MAGNESIA.
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.
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.
EXPERIMENT I.
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.