TECHNOLOGY. 601 



THE PROTECTION OF IRON SURFACES 



against atmospheric influences by providing them with a skin 

 of oxide, obtained either by the action of superheated steam 

 or hot air allowed to act upon the iron kept at a high tempera- 

 ture, appears to have demonstrated its utility for the purpose. 

 From the discussion which the presentation of the plans of 

 Barff", Bowers, and others called forth in the technical soci- 

 eties, the general principle was held to be correct, that " met- 

 als are best protected against atmospheric influences by a 

 film of their own oxide." 



BALATA, 



which is described as the milky sap of the Bully-tree, has late- 

 ly become an article of commerce as a substitute for gutta- 

 percha, which it resembles very closely, though affirmed to 

 be superior to it in. some respects. The following are some 

 of its properties : It is tasteless, has an agreeable odor when 

 warmed, may be cut like gutta-percha, is tough and leathery, 

 and far more elastic than gutta-percha. Like the latter it be- 

 comes soft, and may be joined piece to piece at about 120 

 Fahr., but will not melt until 270 has been reached. It is 

 completely soluble in the cold in benzole and carbon disul- 

 phide. Turpentine dissolves it on heating, while anhydrous 

 alcohol and ether only partially dissolve it. It becomes 

 strongly electrified by friction, and is a better insulator of 

 electricity than gutta-percha, which latter property may 

 make it valuable for electrical and telegraphic purposes. 

 Caustic alkalies and muriatic acid do not affect it, but, like 

 gutta-percha, it is destroyed by concentrated sulphuric and 

 nitric acids. 



Balata appears, therefore, to stand between caoutchouc and 

 gutta-percha in its properties, on which account it may for 

 many uses be found to be more valuable than either of them. 

 Dr. Riegler, who described the new gum in a recent paper 

 before the Niederoesterr. Gewerbeverein, after speaking of the 

 abundance of balata, the increasing demand for elastic gums, 

 and the reckless destruction of the trees which supply rub- 

 ber and gutta-percha, declared it to be "a matter for con- 

 gratulation that the world had been supplied with another 

 and abundant source of elastic-gum, to swell the supply which 



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