Aluminium. 185 



causes it to answer admirably for spectacles, the beams of 

 delicate balances, sextants, etc. It is well adapted for small 

 chemical weights : the increased size of which causes them to 

 be more easily moved, and less easily lost. M. Dumas exhi- 

 bited to the Academy of Sciences a helmet of aluminium, which 

 was very brilliant, had been gilt by the battery, and was joined by 

 solder with great solidity; it weighed less than twenty-five ounces 

 avoirdupois. If of brass, it had weighed nearly sixty ounces, 

 and would not have been so strong. Aluminium cannot easily 

 be adulterated, because even small quantities of other metals 

 deprive it of malleability and ductility. Nor can it be imitated 

 by other metals, for their weight would betray them. All the 

 other less oxidizable metals are heavy, and have a much greater 

 atomic weight. Its point of fusion is somewhat higher than 

 that of zinc, and lower than that of silver. It flows readily into 

 moulds of metal, or sand; any flux would be injuripus to it, 

 but it requires none. It fuses very slowly, for its specific heat 

 is very high, and therefore its latent heat is considerable — it ex- 

 ceeds all ordinary metals in this respect. It therefore keeps 

 warm for a long time, which may be found a useful property. 

 If pure, it is scarcely affected even by the oxyhydxogen 

 blowpipe, but the presence of oxidizable metals facilitates its 

 oxidation. Though silicium has itself little tendency to unite 

 with oxygen, its presence causes aluminium to burn with great 

 splendour, silicate of aluminium being produced. In the form 

 of a thin plate, it burns with great brilliancy, in the flame of a 

 spirit-lamp ; but the light it emits in combustion becomes in- 

 tense, when the flame is urged with a jet of oxygen. If pure, 

 or nearly so, it is not tarnished by air or moisture ; it may be 

 fused in the atmosphere without oxidation, and may even be 

 raised in a cupel to a temperature higher than is required for the 

 assay of gold, without being altered. Water, either as a liquid 

 or vapour, has no effect upon it, though heated to near its melt- 

 ing-point : and at a white heat, produces only a slight oxidation. 

 But if chlorine is present, it acts upon it like a hydracid, hydro- 

 gen being disengaged, and a soluble compound formed. If, how- 

 ever, it is in the form of a thin plate, it will cause a small quan- 

 tity of hydrogen to be evolved, when it is placed in boiling 

 water, 



Nitric acid, whether concentrated or dilute, has no effect 

 upon it, at ordinary temperatures ; it is slowly dissolved in boil- 

 ing nitric acid, but the solution ceases if the acid is allowed to 

 cool. Sulphuric acid, whether concentrated or dilute, does not 

 act upon it ; nor is it, like zinc, rendered soluble in the acid by 

 contact with another metal. But it is dissolved by hydrochloric 

 acid, whether concentrated or dilute ; slowly if pure, but with 

 great rapidity if otherwise. It is the acid, and not the water 



