nion from that gentleman, both with regard to the fufficiency, certainty and utility of these characters; and I hope foon to fee the grounds of their diffent clearly stated and fufficiently established.

However before such descriptions can be carried to that degree of perfection, to which the acute obfervations and accurate diftinctions of a Werner, have raised them amongst the Germans, it will be neceffary both to adopt new words into our language, and to fix more precisely and mineralogically the meaning of those we have already.

On the EFFECTS produced by DIFFERENT COMBINATIONS of the Terra Ponderofa given to Animals ; by Mr. JAMES WATT, jun.

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READ NOVEMBER 13, 1789.

T the Time of writing the foregoing Paper, I confulted Dr. Leigh's Natural History of Lancashire, Chefbire, &c. in hopes of meeting with fomething illuftrative of the Antiquity of the Mine of Anglezark, and, though deceived in my expectations in that refpect, I was much struck with a curious paffage, which feemed to point out fome remarkable properties of the Aerated Barytes unnoticed by later Writers. It is as follows. VOL. III.

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"There are different kinds of Spars; as to "their internal qualities, fome, if taken inwardly, "will vomit and purge moft violently, as that "in the Lead Mines near Andlefack, in Lanca"fhire; and this no doubt confifts in great "measure of Salt and Sulphur, which I take to "be the reason that it is emetic. But the na"ture of this Spar will more fully be made out "from the fubfequent inftances, and the first is "by calcination, in which you eafily discover "that a pound of this will yield a drachm of Arfenic "at the leaft, lying between the lamellæ of the Spar. Whence therefore this comes to be of fo poisonous a nature is plainly evident; notwith"standing this, the neighbours thereabout will frequently take a fcruple at least of this in fits of "the stone, in whom it vomits, purges and works "violently by Urine; in this cafe as they have

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frequently affured me they have found great "relief; whence the vomiting and purging "proceed is evident as we have before observed, "viz. from the Arfenical Sulphur; as likewise "from that profufe quantity of Urine, which

may fufficiently hint to us what kind of mor"bific matter it is that causes the Diabetes, "both in the quick nefs of its poisonous quality, "and likewise the sweetness of the Urine. "There are fome who have ventured to be fo daring as to take a drachm of this, particularly "one James Barns's wife and child, but, alas! to

"their woful experience they found the fad "effects of it, for in about nine hours afterwards

they both expired. The like quantity of this "in about three hours time will kill a dog; " and it is obfervable that the dog while living "is deeply lethargic, which may farther illuf"trate to us, in malignant Fevers attended with "thofe Symptoms, what kind of matter proba"bly it is that causes thofe Symptoms; but that "is more fully difcuffed in its proper place.

Nay so spreading is the poison of this Spar, "that it has not only been fatal to the creature "that has taken it, but a dog, by licking the "blood of a Swine which had taken it acciden"tally mixed with meal and butter, expired "likewife; and it is farther obfervable, that "the flesh of the Swine was afterwards eaten, "and did no mischief though the blood was "poisonous; because, as we may reasonably "conjecture, the Arfenic had not fpread itself "farther than the mass of the blood."*

Upon reading this paffage, I recollected having been told, by the Miners at Anglezark, that they used the Aerated Barytes in the neighbourhood to destroy Rats, I therefore had little doubt that this must be the Spar above alluded to. And though fome of its effects appeared to be exaggerated and the method of accounting for

them erroneous, yet the fubject feemed well worthy of a nearer investigation. For as Poifons, when properly administered, are generally esteemed the most efficacious remedies, and as combinations of the Terra Ponderofa had already been exhibited, it appeared defirable to trace, upon inferior animals, the effects of a fubftance which promised to be of importance to the health of mankind; at any rate, it was adding one fact more to our knowledge, to become thus acquainted with its pernicious effects. To this purpose I inftituted the following experiments.

EXPERIMENT I. At four o'clock in the afternoon I gave a Terrier bitch, weighing about thirteen pounds, which had been without food that day, one drachm of Aerated Barytes, finely pounded and strewed upon fome broiled beef, to induce her to take it. The first half hour it did not appear to produce any effect. At five o'clock The began to froth at the mouth and to be slightly convulfed; fhe drank a little water, but appeared very lethargic. Between five and fix o'clock she was violently purged, and vomited a quantity of whitish curdled matter, after which the became extremely weak and languid; fhe still continued to froth at the mouth, and refused water, though without any figns of averfion. From fix to feven o'clock, her debility kept gradually increafing, until a complete Paralyfis took place: fhe lay extended, entirely deprived of the command of

her

her limbs and even incapable of removing her head from one pofition to another, fo abfolutely was all mufcular power relaxed, that upon taking hold of the loose skin of her neck and afterwards relinquishing the grafp, it retained the pofition into which it had been forced; her eyes however were ftill moveable, her breathing was tolerably easy, and fhe did not give any figns of acute pain. From seven to eight o'clock, the fame Symptoms continued, without any other alteration than that of her breath becoming more fhort and convulfive. The convulfions became ftronger between eight and nine, and she gave evident tokens of pain. At half paft nine o'clock, the Convulfions and Symptoms of pain had almost ceased, and the lethargic ftupor was confiderably increased. At ten o'clock I left her, her eyes were then funk and half closed, the was totally deprived of fenfation and of motion, except that excited by her fetching breath, fo that her approaching diffolution appeared evident. The next morning fhe was found dead.

On Diffection, both the Ventricles and Auricles of the heart were found filled and diftended with black grumous blood; the ftomach empty, but apparently much inflamed; the bladder empty and perfectly collapsed; the other intertines in their ufual ftate, and the brain alfo perfectly found.

EXP. II. At fifteen minutes after twelve, I gave a Puppy, weighing nine pounds, forty grains. Rr3

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