ART. VII. An Examination of Mr. Henry's Striäures on Glass's Magnefia. By Thomas Glafs, M. D. 8vo. 6d. Baldwin. 1774. ART. VIII. A Letter to Dr. Glass, containing a Reply to his Examination, &c. By Thomas Henry, Apothecary. 8vo. 6d. Johnfon. 1774 ART. IX. A Refutation of Mr. Henry's Strictures &c. By the prefent Proprietor of Glafs's Magnefia. 8vo. 6d. Davis. 1774. M R. Henry's communicating to the Public a procefs for preparing pure magnefia, and an account of certain calcareous impurities which he had detected in fome parcels of the magnefia fold under the name of the late Mr. Glafs, on fubjecting it to calcination, has drawn upon him the fevere animadverfions of Dr. Glass, re-enforced with those of the present Proprietor of that medicine; who, it feems, about two years ago, bought the fecret of the original preparer, at the enormous price of 1500 pounds. For the fubftance of Mr. Henry's Strictures, and for the circumftances which gave occafion to his publication of them, we must refer our Readers to the 49th volume of our Review; [November 1773, page 332, &c.] and fhall proceed to confider, in a collective view, the more essential particulars of this controverfy as contained in the three pieces now before us. In the firft of thefe pamphlets, Dr Glafs undertakes to vindicate the purity of Glafs's magnesia, with a view as he profeffes, though not in the moft decent terms, to prevent the Public from being deceived and impofed upon-and the Proprietor from being injured in his reputation and property,' by Mr. Henry's false affertions, and illiberal practices.'-This paffage is a fpecimen of the urbanity with which the Examiner accofts Mr. Henry in the very first fentence of his performance ! The falfity of Mr. Henry's affertions with refpect to the calcareous impregnation alleged by him to have been communicated to water, by fome parcels of Glafs's calcined magnefia which he had examined, is here attempted to be fhewn by fome proofs of a negative kind, or by experiments made on other parcels of that medicine; the refults of which are faid to have been totally different from those given by Mr. Henry. They were made on part of the contents of one box of Glafs's magnefia, prepared by the prefent Proprietor before Mr. Henry's Strictures on it were publifhed;' and on twenty-one other specimens, which may have been prepared fince the publication of Mr. Henry's critique: for the Author is not fufficiently explicit on this head, though it is a point of fome confequence to his ar gument. We are only told that eleven of them were fent to him by the perfon who prepared them,' who warrants them to be all of different makings;' and that the remaining ten ⚫ were collected from the like number of perfons, who bought it j it fince Mr. Glafs difpofed of his procefs.' All these specimens are faid to have been perfectly diffolved in water acidulated with oil of vitriol; and the Author thence infers that no calcareous earth was contained in any one of them. With respect to the other mode of trial, or that by the fiery ordeal,' as Mr. Henry fomewhere terms it, the Author does not say that any one of these twenty one specimens were fubjected to it but he maintains this fingular doctrine ;—that if Glafs's magnesia were really rendered acrid by calcination, fo as to impregnate water with the difagreeable pungent tafte of quicklime, we are not from thence to conclude, with Mr. Henry, that it contained a calcareous earth. The more fubtilifed particles of the magnesia, firft purified and refined to a certain degree, and afterwards deprived of their fixed air by calcination, may,' he fuppofes, unite with and be suspended by the particles of water,' in the fame manner as the more fubtilifed and finer particles of calcined calcareous earths are known to be diffolved in that fluid: and he further fuppofes that the difagreeable taste of lime, complained of by Mr. Henry in his experiments on Glafs's magnefia calcined, was produced by a volatile alcali extricated from his faliva, by the action of the pure calcined magnefia upon it; in the fame manner as a pungent vapour is raised from that and other animal juices by quicklime, or lime water.' Mr. Henry might have fcreened his veracity, at least, under the shelter of this new hypothefis: on the contrary, in the fecond of these publications, fo far from availing himself of it, he treats it with an air of jocularity. Paffing over his ironical remarks upon it, we fhall obferve that, according to this fingular theory, magnesia, firft purified and refined to a certain degree,' and then perfectly calcined, ought conftantly, we apprehend, to impart to water a limy tafte; but few chemifts, we imagine, have obferved this effect; and indeed the Author himfelf afterwards evidently gives up this novel doctrine; declaring that there is no proof that Glafs's magnefia becomes pungent and difagreeable in the mouth after calcination, except the teftimony of one interested perfon, who-may have affirmed a thing that is not.'-So that Mr. Henry's veracity is queftioned, only for obferving that in fix trials Glafs's calcined magnefia gave water a pungent tafte, which, according to Dr. Glafs's own theory, it ought to communicate to it in every instance. But even fuppofing this theory to be juft, the Author feems to forget that Mr. Henry does not reft his proof folely on the tafle of the magnesia, but pretends to have exhibited the calcareous earth contained in it, in a visible and palpable form, by throwing fixed air into the water. U 4 In In the second of thefe publications, Mr. Henry in a proper and spirited manner defends his moral character, and the justice and accuracy of his experiments, against the imputations and animadverfions of Dr. Glafs. He accufes that gentleman of having, in the foregoing pamphlet, rafhly and wantonly traduced a reputation as fpotiefs as his own; and produces the refpe&able teftimonies of Dr Percival and Mr. Aikin in his behalf, which are as favourable to his character as a man, as they are decifive in verifying his experiments above objected to by Dr. Glaís. Some of these were performed in the pretence of the firft of thefe gentlemen, and were afterwards repeated by him, and still more fully and accurately by Mr. Aikin. The experiments of the latter particularly are by him declared to have been made with the greatest care and attention; and those of both were attended with fimilar refults to thofe indicated by Mr. Henry in his Strictures.' Dr. Glafs, in his Examination,' lays great ftrefs on the fuperior and unequalled lightnefs' of his brother's magnefia, and produces an experiment to prove that Mr. Henry's preparation is one-third heavier than the amazing light magnesia, now fold under the name of Mr. Glafs.' This, circumftance alone, in his opinion, fufficiently proves the fuperior purity of the lat ter: as mag efia is lighter than any of the known absorbent earths or reutal falts; and therefore the purer it is, or the less quantity there is of thefe heavier fubftances mixed with it, it muft neceflarily be proportionally lighter. Mr. Henry appears to us to have been always folicitous to acquire this property for his magnefia, and to have met with fome difficulty in the attempt. In answer to Dr. Glass howcver, and in defence of his veracity against a particular charge cf the Doctor's, he declares that on filling a pill box with fome of his own magnefia, and afterwards with fome prepared by Mr. Glafs, which was procured in 1771, and fome of which he has now by him, his own magnefia was found to be lighter than the latter; weighing only 3 fcruples 17 grains, whereas Mr. Glafs's weighed 4 fcruples and 4 grains. That levity, ceteris paribus, may, afford a prefumption in fayour of the purity of magnefia, is not to be denied; but we cannot readily agree with the learned Examiner that the trying the specific gravity of two different parcels of magnefia affords an accurate, much lefs a fole,. or fufficient teft of their relative purity though the purity of metals, and the ftrength of inflammable fpirits may thus be precifely afcertained. The le vity of magnesia appears to depend, in a great measure, on certain minutie in the conducting of the procefs, which are extrinfical to, or do not affect, the goodness or purity of the preparation. 6 paration. The late Mr. Glafs, in his pamphlet on this fubject, obferves p. 13, that the refult of the process is at one time a powder very fubtil and extremely light; and, at another, when the operation has been repeated with a variation fcarce diftinguishable,' the product has been a very ponderous powder, and fometimes even a fubftance not inferior in hardness and closenefs of texture to a flone. As Mr. Henry feems, by his filence at leaft, partly to acquiefce in Dr. Glass's doctrine on this subject, we shall endeavour to fhew, in a familiar way, that the fuperior purity of magnefia cannot be fufficiently afcertained by its specific gravity; to which Dr. Glafs however affirms that it is exactly proportioned.' He found that the fpecific gravity of Glafs's magnefia is to that of Henry's nearly as 2 to 3; and it appears from a table of the fpecific gravities of magnefia, chalk, and other bodies, given in the third of thefe pamphlets, or the Refutation,' that a specimen of Henry's magnefia was found to be nearly of double the fpecific gravity of Glafs's*. In one fpecimen of Henry's preparation we have found it even to exceed that proportion, while it fully ftood every other known chemical teft of purity, as did likewise the specimen of the Proprietor's magnesia with which it was thus fatically compared. Now it appears from the table abovementioned that this light magnesia of Mr. Glafs's might, for example, bear to have a fixth part of its bulk of chalk added to it, or a quarter of its bulk of crabs' claws; or even fo large a portion as a third of its bulk of flacked lime mixed with it; and yet the magnefia, thus grossly adulterated, would by the propofed statical teft be found fpecifically lighter than the fpecimen of Henry's magnefia laft mentioned, in which nevertheless no impurities could be detected by the nicest chemical tefts. In fhort, it is evident that, if fpecific gravity is folely or principally to be attended to, in determining the purity of magnefia, no lefs a quantity than a third, or a half, or more of Henry's magnesia (fuppofing Glass's to be perfectly pure) muft confift intirely of impurities :—a fuppofition too abfurd to be admitted: for how can it be fuppofed that fuch a load of impurity can lie concealed in it, and elude every nicer chemical criterion;-open only to detection through the fingle medium of a pair of scales ? In the third of these publications, or the Refutation,' the ponderofity of Mr. Henry's magnefia'is ftill further infifted upon, • A cubic inch of Glass's magnesia of my own preparing weighed of Mr. Henry's of lime flaked in air a 44 grains, 83 272 153 Refutation, page 19.. as as a matter of reproach; and the levity of the Proprietor's magnefia is held up, as being univerfally admitted to be the most unquestionable test of purity.' The other allegations in favour of this preparation are, that its specific gravity is almoft invariably the fame, as is the lofs of weight which it fuftains by calcination-circumftances which clearly prove that it is always prepared according to a certain invariable standard, namely that of purity;' whereas Mr. Henry's magnefia has no such ftandard different parcels, calcined and uncalcined, varying confiderably in this particular. A fet of experiments on the two rival magnefias is likewise given, which were made under the infpection of Dr. Smith, Dr. Vivian, Dr. Parfons, and Dr. Wall, in the univerfity of Oxford. From these experiments we collect that neither of thefe preparations, when calcined, was rendered cauftic, or gave water the tafte of lime; but it is obferved that, on impregnating with fixed air the water in which Henry's calcined magnefia had been infufed, a perceptible sediment was found at the bottom of the glass the day after the experiment had been performed: whereas no precipitation could be perceived, either at the time, or ever afterwards, in the water, impregnated with fixed air, in which Glafs's magnesia had been digefted. Farther, Glafs's magnefia, both calcined and uncalcined, is faid to have been more readily and perfectly diffolved in the vitriolic acid, than Mr. Henry's preparation.-Thefe experiments certainly prove that the prefent Proprietor can make pure magnesia. These are the most material, though not the moft obfervable parts of this performance, which contains the moft illiberal and indecent reflections on the character of Mr. Henry; who is reprefented and treated in it as an unprincipled intruder on what the Author feems, fomewhat mistakenly in our opinion, to confider as his freehold, in confequence only of a private tranfaction between him and the late Mr. Glafs. In one place Mr. Henry's • veracity,' is faid to be as light as his magnefia is heavy ;' and in other parts of it, he is reprefented as fcandaloufly' invading the Author's property; and as meanly and criminally attempting to gratify his avarice, or relieve his neceffities, at the expence of the Proprietor's reputation and fortune; and, in fhort, is charged, with a want of every principle of integrity.'-To justify fuch language as this, the moft" damning proofs" would scarcely be fufficient. We can find however no fuch proofs, or even prefumptions, in either of thefe productions. Such grofs abufe muft indifpofe every liberal mind against the cause which it is employed to fupport; when they reflect to what kind of treatment an honest man is liable to be expofed, for giving useful information to the Public, whenever fuch information tends to disturb a proprietor in the quiet enjoyment of the sweets of a lucrative monopoly. ་་ན་ B ART. |