502 THE RARER METALS AND THEIR ALLOYS. 



effect of an electric current. In this crucible there is an intimate mix- 

 ture, in atomic proportions, of oxide of chromium and finely divided 

 metallic aluminum. The thermo junction (A, fig. 1, PI. XXIII) of the 

 pyrometer which formed the subject of my last Friday evening lecture 

 here is placed within the crucible B, and the spot of light 0, from the 

 galvanometer D, with which the junction is connected, indicates on the 

 screen that the temperature is rising. You will observe that as soon as 

 the point marked 1,010° is reached energetic action takes place; the 

 temperature suddenly rising above the melting point of platinum, melts 

 the thermo junction, and the spot of light swings violently; but if the 

 crucible be broken open you will see that a mass of metallic chromium 

 has been liberated. 



The use of alkaline metals in separating oxygen from other metals is 

 well known. I can not enter into its history here, beyond saying that 

 if I were to do so, frequent references to the honored names of Berze- 

 lius, Wohler, and Winkler would be demanded. 1 



Mr. Vautin has recently shown that granulated aluminum may read- 

 ily be prepared, and that it renders great service when employed as a 

 reducing agent. He has lent me many specimens of rarer metals which 

 have been reduced to the metallic state by the aid of this finely- 

 granulated aluminum; and I am indebted to his assistant, Mr. Picard, 

 who was lately one of my own students at the Poyal School of Mines, 

 for aid in the preparation of certain other specimens which have been 

 isolated in my laboratory at the mint. 



The experiment you have just seen enables me to justify a statement 

 I made respecting the discriminating action which certain metals appear 

 to exert. The relation of aluminum to other metals is very singular. 

 When, for instance, a small quantity of aluminum is present in cast 

 iron, it protects the silicon, manganese, and carbon from oxidation. 2 

 The presence of silicon in aluminum greatly adds to the brilliancy with 

 which aluminum itself oxidizes and burns. 3 It is also asserted that 

 aluminum, even in small quantity, exerts a powerful protective action 

 against the oxidation of the silver-zinc alloy, which is the result of the 

 desilverization of lead by zinc. 



Moreover, heat aluminum in mass to redness in air, where oxygen 

 may be had freely, and a film of oxide which is formed will protect the 

 mass from further oxidation. On the other hand, if finely divided alu- 

 minum finds itself in the presence of an oxide of a rare metal, at an 

 elevated temperature, it at once acts with energy and promptitude, and 

 releases the rare metal from the bondage of oxidation. I trust, there 

 fore, you will consider my claim that a metal may possess moral attri- 

 butes has been justified. Aluminum, moreover, retains the oxygen it 



1 An interesting paper, by II. F. Keller, on the reduction of oxides of metals by other 

 metals, will be found in the Journal of the American Chemical Society, December, 

 1894, page 833. 



2 Bull. Soc. Chim. Paris, Vol. XI, 1894, page 377. 

 3 Ditte, Lecons sur lcs M/taux, Part II, 1891, page 206. 



