MECHANICS AXD USEFUL APwTS. 23 



rolled hoop link. The advantages of this make are the doing away 

 with welding, and increased strength. In a common chain one bad 

 link destroys the security on which a ship is held, and unless a chain 

 is severely tested, a flaw or imperfect weld may send a vessel and 

 crew to destruction. Sisco and Sinibaldi overcome this defect in weld- 

 ing, which makes the iron brittle, by making rolled hoops homogene- 

 ous. They coil the hoops cold, and the dipping the chain into molten 

 metal, by heating every part equally, consolidates the layers into one 

 mass, and constitutes a really strong chain. In rolling hoop iron in 

 this manner, there is danger of fracture at the bend ; but where there 

 are so many consecutive layers, the fracture of one is of no serious 

 consequence, for its weakness is counteracted by the liquid metal 

 which enters and brazes it to the hoops on either side. The strength 

 of this hoop chain must be comparatively great, for every layer has a 

 skin, and each link is made of sixteen layers, so that the chain is 

 never likely to snap. If one skin is broken, the other fifteen may be 

 intact, and the breakage of one skin will give warning to the crew, 

 whereas, by the existing chain, there is no premonition, and the snap- 



Eing is sudden. In this respect the patented chain of Sisco and Sini- 

 aldi partakes of the character of a rope, whose strands give before it 

 breaks. The links of a good iron cable will be elongated before it 

 parts, but bad iron snaps without distending. The admiralty strain 

 for a 2-inch chain is 72 tons. A chain this same size, made from 

 rolled hoop iron, was tested at her Majesty's yard at Woolwich. It 

 was attached to a testing chain of 2^ inches in diameter, and on the 

 hydraulic power being applied, one of the links was lengthened f of 

 an inch, and the other J of an inch, when it reached a strain of 110 

 tons ; and the 2| inch testing chain broke off in two places when the 

 strain reached 114 tons. The hoop iron chain had some openings in 

 one of the links, which had been imperfectly brazed, but it did not 

 appear to have been made otherwise defective. One link of the 

 same dimensions, 2 inches thick and 2 inches broad, was afterward 

 placed in the testing frame, and when a strain of 70 tons was applied 

 it had lengthened -^ of an inch ; with 80 tons, -| of an inch ; with 

 100 tons, -f-Q of an inch; with 110 tons, | of an inch ; with 115 tons, 

 -j 6 y- of an inch, and when it reached 120 tons' strain it was considered 

 advisable not to continue the strain, as it was so great as to loosen the 

 stone frame on which the machine rested, and liable to damage other 

 parts of the iron frame of the machine. The strain applied on this 

 occasion was one ton more than had ever been previously applied, 

 and the hoop chain was only slightly opened on one side. 



Steel Manufacture. Never before has so complete, and, in some 

 respects, so marvellous a series of specimens illustrating the manufac- 

 ture of steel been witnessed as was shown in the Exhibition building. 

 In order to make clear to the general reader the nature of the various 

 steels here brought together, we propose to state first, as concisely as 

 possible, the properties of steel ; and, secondly, to explain the princi- 

 ples of the various processes by which it is made. In the first place, 

 then, steel may be said to be, essentially, iron containing carbon 

 within certain limits, which cannot be exactly assigned, but which 

 may be taken, approximately, as a half to one-and-a-half per cent. 

 Steel is much more fusible than wrought iron, and may be melted in 



