684 Transactions of the American Institute. 



gas and air was let into the box so as to entirely surround the lamp. 

 Every lamp tried produced an explosion of the gas. The Davy 

 lamp, with a shield on the outside of the wire gauze, exploded in 

 six seconds, with the shield on the inside in nine seconds; the Bel- 

 gium lamp in ten seconds; the Mizard lamp in ten seconds; the 

 small Clany lamp in seven seconds; the large Clany lamp in ten 

 seconds, and the Stephenson lamp in seventy-five seconds. The 

 latter proved to be far superior, but all were shown to be unsafe 

 in a strong current of marsh gas or fire-damp, and should therefore, 

 be regarded merely as indicators of danger when used in mining. 



WHAT MAKES IRON FIBROUS? 



The London Engineermg says when Mr. Bessemer manufactured 

 wrought iron from cast, by blowing air into the molten metal, it 

 was objected to the product that it had no fiber, as common puddled 

 iron had, and that iron without fiber must be necessarily weak. In 

 this inference — which was wholly theoretical — we did not concur, 

 and the question then arose: What does fibrous iron really mean? 

 When the particles of wrought iron are brought to a high tempe- 

 rature without the presence of an intervening material, they cohere 

 in every direction, and the iron is not fibrous. But when slag is 

 intermingled, as in common puddled iron is the case, there are 

 intervening layers of cinder, which, when the iron is passed through 

 rolls, are not wholly expelled, but are only greatly attenuated, and 

 as these planes are then veiy numerous, and pass in every longitu- 

 dinal direction, they prevent, to some extent, the latent adhesion 

 of the particles, which, however, adhere end to end, and a fibrous 

 iron is thus produced. It is now well known that homogeneous 

 iron is much stronger than fibrous iron. But at the beo-innino; of 

 the manufacture, fiber was accounted as necessary in iron as in 

 ropes or thread — a theory resulting merely from the accident of 

 the production of fiber by the modes of manufacture then exclu- 

 sively employed. In the case of iron produced by the common 

 process, any bubble or vacuity in the metal becomes filled with 

 slag, which hinders the sides from being eflfectually welded under 

 the hammer. But in the Bessemer iron, as the slag is absent, the 

 sides of the bubble cohere, when the ingot is subjected to pressure 

 while still hot. It is better to hammer the ingots while still hot, 

 after having been poured, than to allow them to cool and to heat 

 them afterward. For in the one case the heart of the ingot is the 

 hottest part, and in the other the coldest. 



