A L O

ALU

( 46 )

reagents. Hence the authors conclude thataloes contains no gallic acid. The distilledwater of the hepatic aloes gave a sensiblequantity of ammonia.

A second distillation of each species of aloeswas made with the addition of water in theretort. The socotrine aloes gave a pleasantsweet-smelling water, not acid, on which floateda greenish yellow oil smelling like melilot.The distilled water of the hepatic aloes on theother hand was nauseous, and no oil separated.

The action of cold water on aloes wassomewhat different from that observed by M.Braconnot. The latter chemist asserts thatcold water in sufficient quantity will dissolvethe whole of the aloes, and that the lastdissolved portion equals the first in bitterness.On the other hand, the authors of the presentpaper found that by digesting the aloes withsuccessive portions of cold water, and pouringoff the liquors after remaining for some hoursin contact till nothing more was extracted,there remained a soft grey elastic mass in-soluble in water, resembling a resin. Thewatery solution is thick and lathers much onagitation. It deposits a yellow powder on theaddition of a great variety of substances, such asall the mineral acids, all the neutral, and agreat many of the metallic salts. Those ofiron produce a brown precipitate, but differentfrom that given by galls. All these precipitatesfrom the aloetic solution are soluble in water.The watery solution, evaporated slowly to dry-ness, leaves a brown transparent vitriform massintensely bitter, and perfectly soluble in waterand alcohol, but very sparingly in ether.

On the other hand the resinous matter ofaloes is not soluble in cold water, but dissolvesin alcohol and ether, and the latter solution isabundantly precipitated by water.

The action of nitric acid observed by thesechemists was nearly the same as that describedby M. Braconnot. The yellow powder producedby heating aloes in this acid, gives a most beau-tiful purple colour to a large quantity of water.When this powder is gently heated per se in aretort, as soon as it melts, it explodes slightly,and an acid yellow bitter liquor passes into thereceiver, smelling of prussic acid and evolvingammonia on the addition of potash.

Oxymuriatic acid passed through a concen-trated watery solution of aloes is absorbed ingreat quantity, the liquor becomes yellow andcoagulates strongly so as almost entirely tosolidify. This coagulum when washed is elastic,

a Hi. Journ. xvi. p. 233.

insoluble in cold water, but abundantly solublein alcohol, which solution is copiously pre-cipitated by water. The action of oxymuriaticacid therefore appears to convert much of thealoes into a perfect resin.

ALUM.

§ I. Ores and Manufacture of.

The largest alum mine in Britain is at Hur-lett near Glasgow. 1 In the colliery at thatplace is a bed of coal about five feet thick co-vered by a roof of pyritical slaty clay of thethickness of ten inches. The coal with thesuperincumbent roof dips just enough to afforda free passage for the water, and the mine isworked, contrary to the usual practice, fromthe rise to the dip; hence all the workings arenecessarily kept perfectly dry. Tor three cen-turies has this colliery been in work, and itnow presents an excavation the area of whichis nearly a mile square, with pillars of coal atthe usual intervals in order to support the over-lying beds, the thickness of which is cn anaverage about 30 fathoms. The air circulatesslowly through the whole of this space bymeans of such of the old shafts as still remainopen; and, in consequence, a slow decom-position of the roof is perpetually going on.This process however is so gradual that in nopart has the slate been hitherto entirely re-moved.

The first action of the air is to cause a thinflake to scale off from the roof and fall uponthe dry floor; in this last situation the decom-position makes further progress, and by degreesassumes the appearance of a light spicular ef-florence. Succeeding flakes go through a simi-lar process, and in time the whole space up tothe very roof itself is completely filled ; thecurrent of air being then obstructed, ail furtherdecomposition of course ceases till the efflo-resced portion is removed.

The mass thus obtained consists of earth richly impregnated with sulphate of alumine,sulphate of iron, and in some cases with sul-phate of magnesia. The salts are separated bylixiviation from the insoluble residue, the sul-phate of alumine is converted into alum by theaddition of sulphate or muriate of potash, andthe manufacture is finished in the usual way.

The oldest alum works in this countrv areat Whitby in Yorkshire , b where there occurs avast deposit of alum slate about twenty-ninemiles broad from N. to S. and stretching fromthe eastern coast even into Lancashire . Thedepth of this mass is unknown, but it is covered

fc Ph, Journ. xxv. p. 241.