ALU
( 48 )
ALU
washed was dried and finally ignited in a pla-tina crucible. A fresh portion of alum wasthen taken and decomposed by muriat of barytesfor the purpose of ascertaining the amount ofsulphuric acid from the sulphate of barytesproduced. The ammoniacal liquor in the firstprocess was evaporated to dryness, the residualsalt was ignited in order to drive off the sul-phate of ammonia, and the remainder was sul-phate of potash. A fresh portion was boiledin a retort with caustic potash, and the ammo-niacal liquor which came over was saturated
with sulphuric acid and then evaporated ; theremaining sulphate of ammonia indicated theamount of volatile alkali contained in the alum.Lastly, the alumine obtained in the first processwas digested in caustic potash till the whole ofthe earth was taken up, and thus separatedfrom the oxide of iron which is insoluble inthis menstruum. From analyses carried onin the manner just mentioned it appears thatthe following are the component parts of thefour varieties of alum examined by M. Vau-quelin, viz.
10.16 Alumine 31.49 Sulphuric acid12.45 Potash0.41 Ammonia0.262 Oxyde of Iron
Roman
Liep-e
10.36 —
10.39 —
10.21
31.82 —
31.49 —
31.64
12.17 —
12.17 —
12.20
0 . —
0.29 —
0.47
0 . —
0.098 —
0.246
54.35 — 54.438 — 54.766 — 54.772
What remains to be added to each, that theoriginal 100 parts may be complete, is waterof crystallization.
Hence it appears that the sole differencebetween the most and the least valued kinds ofalum is that the latter contains a few thous-andths of the sulphates of ammonia and of iron,which are wholly or almost wholly wanting inthe former. It became therefore a matter ofimportance to ascertain by direct experimentthe effect of a small portion of these salts uponthe more delicate dyes, and in consequence aninvestigation to this purpose was undertakenby M. M. Thenard and Roard. a
The result of their inquiry has been, that indying wool with the most delicate colours, suchas weld, cochineal, sumach, madder and kermes,the use of Roman instead of common alum isof little or no consequence •, that the colours ofcotton are sensibly deteriorated by the employ-ment of impure alum, and that this effect isstill more sensible in the dying of silk. Sul-phate of ammonia even in much larger dosesthan it exists in the most impure alums is verylittle injurious, it is therefore the sulphate ofiron that produces all the mischief.
Having thus ascertained that the preferencegiven to the Roman over every other kind ofalum in the market is by no means a prejudice,but founded on very substantial reasons, M. M.Thenard and Roard proceed to show that it isvery easy to get rid of the sulphate of iron, andthus to raise the most impure alums compleatlyto the standard of the Roman. For this pur-pose the alum is to be dissolved in as small a* Ann. Chim. lix. p. 58.
quantity as possible of boiling water, and thesolution while coding is to be incessantlystirred ; by this means the alum will be ob-tained nearly in a pulverulent state; it is thento be carefully washed two or three times insmall portions of fresh water, and the purifica-tion is compleat. [For the experiments ofThenard and Roard on the action of alum oncolouring matter, see the article Dying in thisAppendix .]
ALUMINUM.
The metallic basis of alumine has not yetbeen obtained in a free state, though sufficientindications of its existence have been made outby Sir H. Davy . a When iron is negativelyelectrified with a high galvanic power and fusedin contact with moistened alumine, a globuleis obtained whiter than pure iron, which slowlyeffervesces in water and becomes graduallycovered with white powder; and the solutionin muriatic acid decomposed by an alkali givesalumine and oxyd of iron. Also when potas-sium is vaporized by heat, and in this statepassed through alumine heated to whiteness,much potash is formed which produces a co-herent mass with the undecomposed alumine,in which are found numerous grey particleswhich become white when heated in the air,and slowly effervesce in water. These greyparticles appear to be an alloy of potassiumand aluminum.
AMMONIA, Ammonium.
The following practicial remarks on thepreparation of the liquid ammonia may be