[f] Hoffman, having attributed the purgative quality of Magnesia to its forming a bitter cathartic salt with the acid it meets with in the stomach and bowels, adds, "At vero in contrarium quoddam dubium contra hanc sententiam moveri posse intelligo, quum nempe alia terrea, quæ prompte solvent et absorbent inhærescens primis viis acidum, neutiquam effectum laxantem exserant. Sed his regerere licet, quod interdum a pulveribus absorbentibus vel bezoardicis utique alvus fluidior fiat, si multum acidi primam regionem incolet: vis tamen eorum purgandi non tanta est, quanta magnesiæ, quia solutiones illorum cum acidis liquoribus factæ non tam eminente salino acri, sed moderate salso sapore imbutæ sunt, quam quidem ea, quæ ex magnesia et acidis liquoribus conficitur. Atque adeo ex eo apparet, præter alcali terreum aliud adhuc esse in magnesia principium, quod ad mixturam acidi in materiem stimulantem et purgantem transeat." Hoffman. Animadversiones et experimenta circa Magnesiam, &c. Op. Tom. 4. p. 480. I have very lately seen a paper signed by Doctor Cadogan and dated in the year 1767, in which he complains grievously of the advertisers of Magnesia, making use of his name without his consent, and has published the process for making _his_ Magnesia. The doctor's intent in this was doubtless benevolent, but his manner of preparing this powder is unnecessarily expensive and wasteful. He directs only one pound of lixivium tartari to five pounds of sal catharticus amarus, which is greatly insufficient to precipitate all the Magnesia. And he insists strongly on the superiority of the lixivium prepared from salt of tartar, to that made of potashes, as if the chemical effects of one, were different from the other. But, says the Doctor, potashes render the Magnesia bitter. Surely the vitriolated tartar produced by a union of one vegetable fixed alkali with the vitriolic acid, is equally soluble in water with that prepared with any other, and if so, will be as easily washed off from the Magnesia. But behold a champion steps forth, and at one blow levels to the ground the whole tribe of Magnesia makers, who have procured it from the factitious Epsom salts. I confess I have not had the happiness to peruse this ingenious gentleman's pamphlet on the subject, but I have formed a very extraordinary opinion of his _candour_, _modesty_, _and knowledge_, from the very curious paper which he distributes with his Magnesia. Notwithstanding Doctor Black, and since him Mr. Glass and several others, have procured _pure_ Magnesia from the factitious Epsom salts, Mr. Dale Ingram, assures us, that he has made an improvement, "which is by the learned esteemed one of the greatest acquisitions to the materia medica." And wherein does this mighty discovery consist? even that Magnesia prepared from the waters of Epsom, is superiour to that prepared from the bitter purging salt; and he assures us that the Magnesia sold by him is so prepared.