Page images
PDF
EPUB

CRYOLITE.

Cryolite was first found at Ivigtuk, in Arksutfiord, west coast of Greenland, where it constitutes a large bed or vein in gneiss. It is a semi-transparent, snow-white mineral. When impure it is yellowish or reddish, even sometimes almost black. It is shining, sp. gr. 2.95, and hardness 2.5 to 3. It is brittle, not infrequently contains FeCO3, PbS, SiO2, and sometimes columbite. It is fusible in the flame of a candle, and on treatment with sulphuric acid yields hydrofluoric acid. As will be seen further on, cryolite was first used by the soapmakers for its soda; it is still used for making soda and alumina salts, and to make a white glass which is a very good imitation of porcelain. The Pennsylvania Salt Company in Philadelphia import it from Ivigtuk by the ship-load for these purposes; lately they have discontinued making the glass. Cryolite is in general use as a flux. A very complete description of the deposit at Ivigtuk can be found in Hoffman's Chemische Industrie.'

6

The only known deposit of cryolite in the United States is that found near Pike's Peak, Colorado, and described by W. Cross and W. F. Hillebrand in the American Journal of Science,' October, 1883. It is purely of mineralogical importance and interest, occurring in small masses as a subordinate constituent in certain quartz and feldspar veins in a country rock of coarse reddish

granite. Zircon, astrophyllite, and columbite are the primary associated minerals, the first only being abundant.

There is no duty on the imports of cryolite into the United States, and they have varied from 10,000 tons in 1869 to 9000 in 1884, costing $9 to $10 per ton.

CORUNDUM.

"Till 1869, the sole sources of corundum were a few river washings in India and elsewhere. It was found in scattered crystals, and cost twelve to twenty-five cents per pound. In 1869, in riding over a spur of the Alleghenies in northern Georgia, I found what has proven to be an almost inexhaustible mine of corundum in the crysolite serpentine, the first instance on record of the mineral being found in situ. Previously it had been washed out of débris at Cripp's Hill, N. C., and at a mine in West Chester, Pa., both on the slopes of the crysolite serpentine. The clue being thus obtained accidentally, about thirty mines were shortly afterwards discovered in the same formation; but of the thousands of tons thus far dug out, the larger portion has come from the mines I discovered.

"At present it can be bought at about ten dollars per ton at the mines. It is nearly pure A1203.

* Mr. W. P. Thompson.

Disapore, a hydrated alumina, is also found in the same region and locality. Corundum will probably always be the principal source in America of material from which to manufacture pure Al. But in Great Britain, in all probability, manufacturers must look to alumina prepared artificially from cryolite or from Mr. Kynaston's sulphate of alumina."*

*Journal of the Society of Chemical Industry, April, 1886.

PART III.

PHYSICAL PROPERTIES OF ALUMINIUM.

COMMERCIAL aluminium is never chemically pure, and therefore displays properties varying more or less from those of the pure metal according to the character and amount of impurities present. In this treatise, whenever the properties of aluminium are mentioned, they must be understood to refer to the chemically pure metal, and not to the commercial article, unless specifically stated. As preliminary to the presentation of these properties we will here make some observations on the commercial metal and the impurities generally found in it.

In whatever way aluminium may be reduced, still it is always far from being pure, being contaminated with iron, silicon, or even sodium and lead, as is shown by the following analyses:

[blocks in formation]

According to Rammelsberg (Kerl's Handbuch) the Si which is always found in aluminium is in part combined with it, and this combined Si changes by treatment with HCl into either SiO2, which remains, or into SiH, which escapes; while another part of the Si is combined with the aluminium just as graphite is with Fe; and this part of the Si remains on treatment with acid as a black mass, not oxidized by ignition in the air. Two analyses of aluminium reduced from cryolite by sodium in a porcelain crucible gave—

[merged small][merged small][ocr errors][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small]

One sample of aluminium analyzed by Professor Rammelsburg contained as much as 10.46 per cent. Si, and another sample even 13.9 per cent. The quantity of Fe varies from 2.9 to 7.5 per cent.

M. Dumas has found that aluminium usually contains gases, about which he makes the following statements:* "On submitting aluminium in a vacuum to the action of a gradually increasing temperature up to the softening point of porcelain, and letting the mercury pump continue acting on the retort until it was completely exhausted, considerable quantities of gas were withdrawn. The liberation of the gas from the metal seems to take

*Sci. Am. Suppl., Aug. 7, 1880.

« PreviousContinue »