[o] The reader is referred for further information on this subject, to an excellent Treatise on the Management of Pregnant and Lying-in Women, lately published by my worthy and ingenious friend Mr. White; to a volume of Experiments and Observations, by Dr. Percival, which is now in the press; and to some very curious papers on factitious air, which have lately been communicated to the Royal Society, by Dr. Priestley.
[p] In making this experiment some time since, I imagined that Doctor Black had been mistaken in this point, and that some impurity in the water had prevented the success of his process, for I found the water impregnated, as I supposed, with the Magnesia. Flushed with my supposed success, I proceeded to make experiments on the lithontriptic powers of this water, which I found to be very considerable, acting more efficaciously on the human calculus, than either oyster-shell lime water, or a dilute solution of soap ley. I communicated this interesting intelligence to some of my medical friends; but on repeating my experiment several times with different parcels of Magnesia, that the truth of the fact might be absolutely ascertained, I at last was convinced, to my no small mortification, that what I had too sanguinely flattered myself to be a discovery likely to be highly serviceable to mankind, was founded on error; and that the properties communicated to the water proceeded from some calcareous matter which the Magnesia had received by being washed with impure water. I mention this as a caution to every young experimentalist, to be extremely careful in drawing conclusions. However, as something may be learned, even from an unsuccessful experiment, it proves that a very small quantity of lime is sufficient to impregnate a large quantity of water; for I used the calcined Magnesia, in the same proportion as lime is directed for making lime-water, so that very little of it could be quick-lime. And as oyster-shell lime water is a superiour solvent of the calculus to the water prepared with stone lime, is there not some reason to think that the calcareous earth, which has been dissolved in hard water, may, when calcined, be a more powerful lithontriptic, than either of the others? If any inference can be drawn from it, which may in the least promote the interests of mankind, I shall be sufficiently recompensed for the humiliating circumstance of recounting an erroneous experiment.
[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.
[r] I at that time overlooked an experiment of Dr. Macbride's which proves Magnesia to be septic to animal flesh; but having met with it just before these papers were going to the press, I take this method of acknowledging it.
[s] Doctor Macbride found that pulv. e chel. c. c. hastened the corruption of bile: might not this depend on some variety in the composition of that powder? Chalk and oyster shells are often substituted in the hospitals and by the druggists, for the other ingredients.
[t] Vid. Lectures on the Materia Medica, as delivered by William Cullen, M.D. p. 195.
[u] Percival's Essays Medical and Experimental, 2d Edit. p. 65.
[v] See Dr. Percival's Experiments and Observations, p. 72; Dr. Priestley's papers on factitious air; and Mr. White's Treatise on the Management of Pregnant and Lying-in Women, p. 203.
[w] See Dr. Priestley's Directions for impregnating Water with fixed Air.