186 A luminium. 



in which the acid is dissolved, that is decomposed; since hy- 

 drochloric acid gas acts upon it at a very low temperature, 

 forming an anhydrous and very volatile chloride ; and the more 

 concentrated the acid, the more energetic its effect. Whenever 

 aluminium is tarnished with water, on testing with nitrate 

 of silver, it will be found that chlorine is present. If a wire 

 of aluminium is plunged for an instant into dilute hydrochloric 

 acid, a considerable amount of it will be changed into a white 

 substance, after it has been withdrawn from the acid, and 

 without any absorption of oxygen. Acetic acid, diluted to 

 the strength of strong vinegar, has little or no effect upon it ; 

 but it is important to bear in mind that a mixture of vinegar 

 and salt dissolved in water, acts upon it — in accordance with a 

 well-known chemical law, according to which the acetic acid 

 displaces some of the chlorine, and this forms hydrochloric 

 acid, its proper solvent ; but the action in such a case is very 

 slow, particularly if the metal is pure. Tin would be more 

 affected in the same circumstances, and would impart a bad 

 taste, which does not occur with aluminium. It is scarcely 

 acted on by tartaric acid — a valuable property, if it is used 

 in connection with wines. Its combinations with the fee- 

 ble acids are harmless, which is not the case with most of 

 the other metals ; and they are decomposed at a low tempera- 

 ture. Solutions of potash and soda act upon aluminium very 

 energetically, forming aluminates of the alkalies, with evolution 

 of hydrogen. But monohydrates of the alkalies, even at a red 

 heat, affect it no further than to remove from its surface any 

 silicium that may be present upon it. Ammonia acts upon it 

 slightly, but only in presence of water — which is decomposed, 

 hydrogen being set free : and the resulting alumina is dissolved 

 by the alkali. Sulphur has no action upon it, even when it is 

 heated to redness : but enters into combination with it at a high 

 temperature. Its utility, as applied to domestic purposes, is 

 increased by its not being tarnished by the sulphur which is in 

 eggs and mustard. Sulphuretted hydrogen does not affect it : 

 hence the air of cities, which always contains that compound, 

 particulai-ly when they are lighted with gas, does not dim its 

 lustre, though it tarnishes silver with great rapidity. It may 

 be used therefore as a reflector, with a jet of gas, even though 

 the flame comes occasionally in contact with it. If sulphuret 

 of ammonia is evaporated from it, there will be produced only 

 a spot of sulphur, which will be driven off by continuing the 

 heat. Polysulphuret of potassium will merely act on any iron 

 or copper that may be united with it : but that substance can- 

 not be applied to its purification, since it would more or less 

 protect these metals, and prevent their complete removal. 

 Metallic salts comport themselves with aluminium according 



