Two or three years had elapsed since I had seen any of Mr. Glass's Magnesia, except a small quantity which I had preserved, as a standard for the levity of what I prepared myself. But having a mind to calcine some of his, in order to compare it with my own, I sent for a box from Mr. Harrop, an agent of the proprietors in this town. I was surprized, on opening if, to find the Magnesia specifically lighter, to an amazing degree, than any I had formerly seen, insomuch that the six shillings box, which used to contain about four ounces, now only contained an ounce and half, Troy weight: _so that this medicine is sold at the rate of two pounds eight shillings the Troy pound, which is not fourteen ounces Avoirdupois_. On attempting to dissolve it in the vitriolic acid, I found the solution very imperfect; and on calcining half of the contents of the box, it was with indignation that I discovered this Magnesia, so extolled, so puffed in every newspaper, for _its superior purity and goodness_, to contain no inconsiderable quantity of calcareous earth; for the pungency of it was very disagreeable in the mouth, and one scruple of it impregnated an ounce of water almost as strongly as so much lime would have done. These are tests, which, tho' much stronger than that of levity which the proprietors have artfully placed as the principal one, they have avoided mentioning, being sensible of its deficient solubility, and that it would not stand the FIERY ORDEAL. Willing, however, to believe that this impurity might be accidental, though I had reason to think, from the artful conduct above alluded to, that it was not so, I sent for a box of Magnesia, from the agent for the sale of Mr. Glass's Magnesia at Preston. This likewise proved calcareous, though I thought the lime, produced by calcining it, not quite so pungent as the other; it, however, made a strong lime-water. That I might avoid drawing too hasty conclusions, I procured a third box from Chester, which being subjected to the same trials, seemed more impure than either of the other two. This Magnesia formed a very imperfect solution in the vitriolic acid; and the taste of the lime, after calcination, was so very disagreeable, that I was not free from it for some hours. The water impregnated with it was as strong to the taste as common lime-water, and the precipitate which fell from it, on blowing air into it, was as copious as I ever observed from that prepared with stone or oyster-shell lime. The boxes were all purchased from the agents for the sale of Glass's Magnesia, and every box was sealed with his arms, and had every other mark of authenticity. I have retained samples of each in both states.