MECHANICS AND USEFUL ARTS. 23 



PROTECTION OF IRON FROM RUST. 



At a recent meeting of the Society of Arts, London, the question of 

 preserving iron from rusting formed a subject of conversation. It was 

 stated that galvanized iron wire for telegraphs was not affected with 

 rust in passing through the rural districts of England ; but that the 

 coating of zinc on the iron afforded no protection to wires in cities. 

 The acid gas generated by the combustion of fuel attacked the coating 

 and decomposed it. A new substitute for covering telegraphic wire 

 was desirable. 



With respect to paints for coating iron, such as the plates of iron 

 vessels, machinery, &c., Mr. John Braithwaite stated that pure red lead 

 was the best. His experience dated as far back as 1806, with the use 

 of red lead, and for fifty years he had used it with success. White 

 lead was more injurious than beneficial as a paint for iron. In April 

 last, he inspected a well, two hundred feet deep, a short distance out of 

 London, where he had put up an engine forty-five years ago ; the long 

 iron rods which had been placed in it had been painted with red lead, 

 and the metal had remained unchanged in all that period. The same 

 preservative effects of red lead paint on iron, he had witnessed upon 

 other iron-work which had been many years in use. 



ALUMINUM BRONZE. 



It has long been an object with scientific inquirers to reduce the 

 weight of the philosophical instruments which they have to employ. 

 Especially is this the case with magnetical and astronomical instru- 

 ments used in the triangulation of a country for a survey, or the highly 

 important operation of measuring an arc of the meridian. Aluminum 

 bronze supplies the long-sought desideratum. This metal is produced 

 from a mixture of ten per cent, of aluminum with pure copper ; and a 

 most remarkable metal it is. Col. Strange, in a recent communication 

 to the Royal Astronomical Society, thus enumerates some of its proper- 

 ties: Good gun-metal will break with a strain of 35,000 Ibs. to the 

 square inch; aluminum bronze requires 73,000 Ibs to the square inch 

 to break it. It resists compression equally well ; it is malleable when 

 heated ; can be easily cast, and behaves well under the file. " It does 

 not clog the file ; and in the lathe and planing-machine, the tool re- 

 moves long elastic shavings, leaving a fine, bright, smooth surface." 

 Moreover, " it can be worked with much less difficulty than steel ; tar- 

 nishes less readily than any metal usually employed for astronomical 

 instruments, and is less affected by changes of temperature than either 

 gun-metal or brass." This latter quality is especially important in in- 

 struments used for surveying in the tropics, as expansion by heat would 

 very much impair their accuracy. It is remarkably well fitted to re- 

 ceive graduation, as it takes a fine division, which is pure and equable, 

 surpassing any other cast metal in this respect. Col. Strange remarks 

 that in its elasticity it is said to surpass even steel, and it would there- 

 fore appear to be the most proper material for the suspension strings of 

 clock pendulums. 



C. Tissier, Director of the Aluminum Works at Rouen, shows that 

 one per cent, of aluminum in copper makes the latter more fusible, 

 giving it the property of filling the mould in casting, at the same time 



