200

place suddenly towards a red-white heat. grammes of aluminium, occupying 80 c. c., gave 89.5 c. c. of gas, measured at 17° and 755 mm. pressure. The gas consisted of 1.5 c. c. CO2 and 88 c. c. H. CO, N, and O were absent."

*The aluminium apex or cap of the Washington Monument cast by Colonel Frishmuth, of Philadelphia, has the following composition:—

Deville: The color of aluminium is a beautiful white with a slight blue tint, especially when it has been strongly worked. Being put alongside silver, their color is sensibly the same. However, common silver, and especially that alloyed with copper, has a yellow tinge, making the aluminium look whiter by comparison. Tin is still yellower than silver, so that aluminium possesses a color unlike any other useful metal.

Fremy: Aluminium has a fine white color, just a little blue when compared with silver. When it has been worked, or when it contains Fe or Si, its blue tint acquires greater intensity. The commercial aluminium resembles silver.

* Mineral Resources of the United States, 1883-84.

Mallet: Absolutely pure aluminium is perceptibly whiter than the commercial metal; on a cut surface very nearly pure tin-white, without bluish tinge, as far as could be judged from the small pieces examined.

Mierzinski: The pure white color of aluminium is very brilliant; it has a tint lying between the color of tin and zinc, although on account of its usual blue shading, even in a poor light, it cannot be confounded with them or with any white metal.

MAT.

water and at

Deville: Aluminium like silver is able to take a very beautiful mat which keeps indefinitely in the air. It is obtained easily by plunging the surface for an instant in a very dilute solution of caustic soda, washing in a large quantity of last dipping in strong nitric acid. Under these conditions, all the foreign materials which might contaminate it, except silicon in large proportion, dissolve and leave the metal quite white and with a very pleasing appearance.

Mierzinski: The peculiar lustre of aluminium, however, is not permanent. With time, the objects take on their plain faces an olive green coloration, and look much less agreeably. Their former white color can be restored by Mourey's receipt, by placing them first in dilute hydrofluoric acid, 1000 parts

water to 2 of acid, and then dipping them in nitric acid.

Bell Bros. They recommend first washing the objects in benzole or essence of turpentine, before treating with NaOH and HNO3, as above.

POLISH AND LUSTRE.

Deville: Aluminium may be polished and burnished easily, but it is necessary to employ as an intermediate material between the stone and polishing powder a mixture of stearic acid and essence of turpentine, finishing with pure essence of turpentine. In general, the polished surfaces are of a less agreeable appearance than the mat, the blue tint of the metal becoming more manifest. But, in this work, the experience and practice of the workers in aluminium is far from being complete; each metal requires a special way of working, and we may expect yet for a material so new that progress will be made in this direction.

Bell Bros.: Aluminium is easily polished and burnished. Use a mixture of equal parts of rum and olive oil as an intermediate substance between the polishing stone and the powder used. The polishing stone is steeped in this mixture, and will then burnish the metal as silver and copper are burnished, care being taken not to press too heavily on the burnishing instrument.

Kerl & Stohman: The use of the old means of

polishing and burnishing metals, such as soap, wine, vinegar, linseed-oil, decoction of marshmallow, etc., is not effective with aluminium, but, on the contrary, is even harmful; because, using them, the blood stone and the burnishing iron tear the metal as fine stone does glass. Oil of turpentine has also been used, but with no good effect. Mourey found, after many attempts, that a mixture of equal weights of olive oil and rum, which were shaken in a bottle till an emulsified mass resulted, gave a very bril liant polish. The polishing stone is dipped in this liquid, and the metal polished like silver, except that one must not press so hard in shining up. The peculiar black streaks which form under the polishing stone need cause no trouble; they do not injure the polish in the least, and can be removed from time to time by wiping with a lump of cotton. The best way to clean a soiled surface and remove grease is to dip the object in benzine, and dry it in fine sawdust. Hammered and pressed objects of aluminium may, before polishing, be very easily ground by using olive oil and pumice.

ODOR.

Deville: The odor of pure aluminium is sensibly nothing, but the metal strongly charged with silicon will exhale the odor of silicuretted hydrogen, exactly represented by the odor of cast iron. But, even under these unfavorable circumstances,

the smell of the metal is only appreciable to persons experienced in judging very slight sensations of

this kind.

Watts: When pure, aluminium is quite destitute of taste or odor.

TASTE.

Deville: Pure aluminium has no taste, but the impure and odorous metal may have a taste like iron, in any case only very slight.

MALLEABILITY.

Deville: Aluminium may be forged or rolled with as much perfection as gold or silver. It is beaten into leaves as easily as they, and a very experienced gold beater, M. Rousseau, has made leaves as fine as those of gold or silver, which are put up in books. I know of no other useful metal able to stand this treatment. Before rolling a bar of aluminium it is well to prepare the metal by forging it on all sides, and commencing work with a hammer. Aluminium is tempered at a very low red heat; or the plate is heated just until the black trace left on its surface by a drop of oil put there and which is carbonized has entirely disappeared.

Mallet: With absolutely pure aluminium the malleability was undoubtedly improved, the metal