ALUM SLATE. 
is much more serviceable for grease and cracked 
heels in horses; and is also a good remedy for 
such kinds of swellings in the legs as are attended 
with exudation of moisture. Some practitioners 
ignorantly and absurdly add Goulard’s lotion to 
this solution ; and in consequence effect a chemi- 
cal decomposition, which transmutes the whole 
astringent contents of the liquid into alumina 
which possesses very little astringency, and the 
sulphates of lead and potash which possess no as- 
tringency whatever. Alum ointment—which is 
made by melting together one drachm of pow- 
dered alum, one ounce of turpentine, and one 
| ounce of hog’s lard—is occasionally employed as 
a substitute for the lotion when the sores are 
liable to become hard and dry; yet it is of such 
| trifling importance as not to be noticed by some 
of the best masters in veterinary surgery. Alum 
| whey, made by dissolving two drachms of the 
| powder in a pint of hot milk, is often adminis- 
tered to the horse in cases of diarrhoea; and though 
| it may sometimes succeed when other remedies 
fail, it is by no means so good an astringent as 
_eatechu or kino. This remedy, however—espe- 
| cially if a drachm of ginger be added in every 
case, and also a scruple of opium in a case of very 
violent purging—is eminently suitable for diar- 
| rhoea in the cow. If alum be mixed with any 
vegetable astringent, the peculiar power or astrin- 
gency of both is diminished. Burnt alum—pre- 
pared by burning a piece of alum on an iron plate 
till it becomes quite dry and opaquely white—is 
greatly milder than the alum itself, and therefore 
may be a less objectionable remedy for specks in 
| the eye, but possesses too little causticity to be 
a proper application for wounds.— Ure’s Diction- 
ary of Chemistry.—Anderson’s Commercial Dic- 
tionary.— White's Farriery.—Clater’s Catile Doe- 
tor. 
ALUM SLATE. A bluish, argillaceous, schis- 
tose rock, found in most of the hills between Scar- 
borough and the river Tees, and in a considerable 
portion of the mountains of Scotland and Ireland. 
It splits like the Cornish slate ; and it yields, by 
disintegration, a clayey soil. It contains, in con- 
siderable proportions, sulphur, iron, and alumina, 
and is the substance from which alum is chiefly 
prepared artificially. The broken stone is cal- 
cined in heaps, in a furnace like a limekiln, or 
in a reverberatory. It is then exposed to efflo- 
resce, and daily moistened with water for several 
months. The mass gradually sinks, and is con- 
verted into a paste, above which is a liquid con- 
taining a basic alum. ‘This is heated for several 
hours in copper or lead vessels, and when cooled 
and settled, the clear liquor is drawn off into 
erystallizers. A soft variety of it closely resem- 
bles clay-slate in appearance, but, by exposure to 
the air, it forms a saline efflorescence, greatly in- 
creases in thickness, breaks up into exfoliations 
or scales, and speedily undergoes complete disin- 
tegration. Alum slate occurs both in rocky 
masses and in insulated balls. Some varieties of 
ALUMINA. 147 
clay slate are often confounded with alum slate. 
See Cray SLATE. 
ALUMINA. The pure earth or characteristic 
matter of clay. It was called alumina in conse- 
quence of having been obtained in a state of the 
greatest purity from alum, by the chemical ab- 
straction of the potash and the sulphuric acid 
with which it is there combined. The oriental 
gems, ruby and sapphire, afford specimens of the 
purest native alumina, for they consist solely of 
this earth, and a small portion of colouring mat- 
ter. When quite or nearly pure, alumina has 
no smell, little taste, and little astringency ; and 
would not be suspected by a sciolist to have any 
relation to either alum or clay. It is exactly 
twice the weight of water; and when heated, it 
parts with a portion of water, and contracts in 
bulk. Its strong affinity for water under low 
temperatures, and the readiness with which it 
gives off water under heat, account for the con- 
stant wetness dnd plashiness of clay soils during 
winter, and for their contractions, crackings, 
hardness, and aridity, after a period of drought 
in summer, Clay always contains a large pro- 
portion of other substances than alumina, some 
in a state of chemical combination with it, and 
some in a state of mechanical mixture or accom- 
paniment; and the earthy smell which it emits 
when breathed upon, is occasioned by the pre- 
sence of oxide of iron. See Cuay. Sir Hum- 
phrey Davy, though he did not succeed in ob- 
taining from alumina a metallic base in a separ- 
ate state, conducted experiments which quite or 
nearly demonstrated that alumina is the oxide of 
a metal which has since been termed aluminum. 
Alumina exists, in a greater or less proportion, 
in all cultivated soils; yet it exerts an influence 
on vegetation, chiefly by attracting and retain- 
ing water and ammonia, and is very rarely found, 
as a separate earth, in the ashes of plants. One 
three-fifths of a grain of alumina are found in 
thirty-two ounces of the grain of wheat, and 
about four grains in thirty ounces of the grain 
of barley or oats. But it constitutes 3°72 parts 
in 100 of the entire plant of the sunflower, 7°11 
of the entire plant of Turkey wheat, and 14 of 
the entire plant of the fumitory. Its principal 
existence and operation in the economy of soils 
and vegetation is in the form of Simicats, SuL- 
PHATE, and PHospHatsE: see these articles. The 
chief aluminous minerals, whose disintegration 
yields alumina to soil, and contributes argilla- 
ceous or clayey earths to arable land, are potash 
and soda felspars, Labrador spar, mica, and the 
zeolites ; and these minerals occur in mechanical 
mixture with other substances in granite, gneiss, 
mica-slate, porphyry, clay-slate, greywacke, clink- 
stone, basalt, greenstone, mountain limestone, 
transition limestone, dolomite, muschel kalk, and 
various sandstones,—rocks which constitute pro- 
bably nine-tenths of all the hills and mountains 
of the three kingdoms, and a very large propor- 
tion of the immediate substrata of plains and 
i — eee 
