10& MAG 
the remaining powder, ftir and decant it in its turbid ftnte, 
and fep'arate the magnefia from the water as before; thus 
the whole, or moll of it, will be reduced to an equal de- 
gree of finenefs. The larger the quantity of water into 
which the precipitated powder is call, the more fpeedily 
and perfectly will the vitriolated tartar, which is formed 
by the union of the alkali with the acid of the fal. cath. 
be wafhed off. The neutral fait thould be walked off as 
quickly as polfible ; othervvife, by allowing the mixture 
to ftand for fome time, the powder concretes into minute 
grains, which, when viewed with a microfcope, appear to 
be aflemblages of needles diverging from a point. Thefe 
concretions cannot be re-diflolved by any walking, how¬ 
ever long continued. Dr. Black orders four times the 
quantity of water to that of the folution for throwing the 
coagulum into ; but Mr. Henry obferves, that this quan¬ 
tity is far too little. The water Ihould be pure ; and 
diftilled water is the belt, provided it be kept till its em- 
pyreuma is gone off. Hard or impure water makes the 
magnefia coarfe and difagreeable. The chalk-ftones on 
-which the magnefia is dried Ihould be expofed to a mode¬ 
rate heat, that the moifture may evaporate quickly ; and 
eleanlinefs fhould be particularly attended to through the 
whole procefs. 
Magnefia is recommended by Hoffman, a? an ufeful 
antacid, a fafe and inoffenfive laxative in dofes of a dram 
or two, and a diaphoretic and diuretic, when given in 
fmaller dofes of fifteen or twenty grains. It is now much 
in ufe, particularly in heart-burns, for correfting acidities 
in the pi imae vis, and for preventing or removing the many 
diforders to which children are fubject on this account. 
It is preferred to all common abforbents, on account of its 
laxative quality, which it manifefts when it meets with an 
acid in the ftomach and bowels. If it is mixed with rhu¬ 
barb, it prevents the rhubarb from leaving a coftivenefs 
behind. If the magnefia be neither accompanied nor met 
with by an acid, it is not purgative, but limply abforbent. 
Objection has been made to the ufe of magnefia by 
Hoffman and others, that it frequently produced flatu¬ 
lencies, gripings/and other uneafy fenfations, particularly 
in weak bowels. It is now well known, that thefe fymp- 
toms unift have been produced by the great quantity of 
fixed air contained in it, and difcharged from it in con- 
fequence of its meeting and effervefcing with an acid in 
the ftomach or inteltines. Dr. Percival, therefore, fug- 
gefted to Mr. Henry the idea of depriving it of its air, 
with a view of obviating thefe troublefome fymptoms oc- 
cafionally attending the ufe of it. For this purpofe the 
magnefia fliould be calcined by putting it in a common 
crucible, placing it in a glowing fire, and keeping it red- 
hot for the fpace of two hours. The magnefia thus treated 
was found to be equally purgatives when given in half its 
-.former dofe ; it is deprived, by this procefs, of the difa¬ 
greeable qualities above mentioned ; and acquires like- 
wife new properties, which render it likely to anfwer fome 
other important practical purpofes. By calcination it is 
not only rendered incapable of generating air in the fto- 
mach and bowels, but it is qualified to abforb, or render 
fixed, that which it finds there, and which is produced, 
fometimes in too great quantities, in the procefs of di- 
geftion ; and it is confequently adapted to relieve thofe 
colics, or other diforders, which are commonly called fla¬ 
tulent. In this refpedt it promifes, as Mr. Henry ob¬ 
ferves, to be much more efficacious than the whole tribe 
of carminatives, from which it effentially differs with re¬ 
gard to its mode of operation and effects. It appears like- 
wife to be the molt proper cathartic for patients afflicted 
with the (tone, who are under a courfe of the foap-ley; 
as it cannot, like the vegetable purgatives, counteract the 
lixivium, by throwing air into it; but, on the contrary, 
inuft abforb a part of that air, which is already in the 
primte vise, and which would otherwife be attracted by 
the caiiftic alkali, and render it lefs capable of aiding on 
the calculus. In order to produce thefe effects, it is of 
^reat importance that the magnefia, intended for calcjna- 
M A G 
tion, fhould be perfectly free from any admixture of cal- 
careous earth ; as, in that procefs, this lad mentioned fub- 
ftance muft neceflarily be deprived of its air, or rendered 
caiiftic; and the magnefia which contains it will accord¬ 
ingly impregnate the water in which it is infufed with the 
talte and qualities of lime-water. Glafs’s magnefia, which 
has been lb highly extolled, appears, by Mr. Henry’s ex¬ 
periments, to contain no inconliderable portion of calcare¬ 
ous earth. Lond. Med. Tranf. vol. ii. Henry's Exp. and Obf. 
1773. 
MAGNE'SIUM, f. Manganese; a genus of metals, 
belonging to the divifion of thofe which are not mallea¬ 
ble. Generic characters—Dark grey, gradually blacken¬ 
ing by expofure to the air; hard, very brittle, of a granu¬ 
lar texture, attracted by the magnet when reduced to pow¬ 
der, unlefs entirely deprived of its iron ; fpecific gravity, 
7; melting with great difficulty; its black oxyd affum- 
ing a green colour, which in a very violent heat is fufed 
and converted into a green glafs; when fufed with bo¬ 
rax, producing a deep red glafs; when diflolved in ful- 
phuric acid, leaving a black fpongy mafs behind, and 
forming a red precipitate with the addition of foda. See 
the article Chemistry, vol. iv. p. 271. 
1. Magnefium regulinum, or native metallic manganefe: 
ftaining the fingers, of a filver-grey colour with metallic 
luftre, and divergingly-foliated texture. Found in the 
valley of Viedeflos, near Lem, in the neighbourhood of 
Foix, on the Pyrenees, in kidney-form maffes. It is 
flightly malleable, and not attracted by the magnet, be¬ 
ing entirely pure, and free from iron. 
2. Magnefium ochraceo, or manganefe ochre: friable, 
without luftre or tranfparency, earthy. Found in Eng¬ 
land, the Pyrenees, the mines of Franconia, and in the 
Altaic mountains of Siberia ; maflive or difleminated, 
cellular, porous, perforated, or in various imitative forms; 
texture earthy. Colour blackifh, or brown like the brown 
haematites. Specific gravity, before it has abforbed water, 
3^707; after abforption, y^o^. 
3. Magnefium piCtorum, or black wad ; black, friable, 
floating ; mixed dry with a. fourth of its weight of linfeed 
oil, producing fpontaneous inflammation. Found in 
Derbyfhire, forming confiderable ftrata ; friable, generally 
fmooth between the fingers. Contains manganefe, oxyd 
of iron, lead, and mica. 
4. Magnefium niveum, or white ore of manganefe: white, 
becoming brownifli or blackifh when heated ; foft, effer¬ 
vefcing with nitric acid, and emitting fulphurated hydro¬ 
gen gas. Found in the mines of Great Britain, Norway, 
Sweden, and Tranfylvania, in round or kidney-form mafles, 
or \/arioufly difleminated, fometimes in loofe fcales. Colour 
white, with often a reddifh tinge : texture either radiated 
or in incurved foliations; before the blow-pipe it gives a 
violet colour to borax. 
5. Magnefium rubrum, or red manganefe: red, co¬ 
louring glafles red. Found near Piedmont and Lem on 
the Pyrenees, in round lumps, or fibrous in a ftellate manner. 
6. Magnefium vulgaris, or native oxyd of manganefe; 
foft, ftaining the fingers, of a fteel-grey colour with me¬ 
tallic luftre. Found in various parts of Great Britain, 
particularly on Mendip-hill in Somerfetfhire; in Sweden, 
France, Germany, Bohemia, Silelia, &c. maflive or difle¬ 
minated, or varioufly imitative; in fmall acutangled qua¬ 
drangular prifms, or fix-fided acicular columns, with the 
faces often longitudinally ftriate. Colour greyifh-white, 
more or lefs dulky, with fometimes a fmall tinge of red ; 
texture feldoni compadt, generally fibrous in a ftellate 
manner, radiated, or foliated, with the fragments indeter¬ 
minate or wedge-fonn or fplintery; foft, brittle, with a 
black or brown ftreak ; before the blow-pipe it becomes 
blackifh-brown, but does not melt, and tinges borax vio¬ 
let. This fubftance is an ingredient in printers’ ink. 
The fpecific gravity varies from 2 to 4^5 it contains 
from thirty, to forty-five per cent, of oxyd of manganefe, 
from thirty to forty of oxygen, and a fmall quantity of 
oxyd of iron, carbonat of lime, barytes, and filex. 
7. Magneffuiu 
