MECHANICS AND USEFUL ARTS. 47 



tion of boilers, pipes, &c. In order to acquire satisfactory data, a 

 variety of plates, manufactured from the best quality of iron, of differ- 

 ent localities, were submitted to direct experiment ; first, by tearing 

 them asunder in the direction of the fibre ; second, across it. The 

 mean tensile strength per square inch, in tons, was found to be 22.16, 

 in the direction of the fibre ; 22.29 across the fibre. From this it will 

 be observed, that there is no difference in the strength of iron plates, 

 whether torn in the direction of the fibre or against it, and this uni- 

 formity of strength probably arises from the superior manner in which 

 that article is now manufactured. The experiments would, however, 

 be imperfect as regards construction, if they had not been extended to 

 the process of riveting ; and on this point our information has been of 

 the most meagre description. Until of late years, many of our numer- 

 ous constructions have been conducted under the impression that the 

 riveted point was not only strong, but absolutely stronger than the plate 

 itself; whereas, more than one third of the strength is lost by that pro- 

 cess. To prove the fallacy of these views, it was ascertained by exper- 

 iment, that the strength of iron plates, as compared with their rivet- 

 ed joints, was not only weakened to the extent of the quantity of 

 metal punched out to receive the rivets, but that in the following 

 ratios, viz., as 1000 to TOO in the double riveted joint, and 1000 to 

 560 in the single riveted joint. From the above facts, practical for- 

 mula have been deduced to show that the maximum resistance of single 

 riveted plates does not exceed 27,000 Ibs. to the square inch ; and 

 taking into account the crossing of the joints, and other circumstances 

 peculiar to sound construction, 34,000 Ibs., or 15 tons to the square 

 inch, has been found to be the maximum strength of riveted plates, 

 such as those used for boilers and similar constructions. In conclusion, 

 attention was directed to several important improvements in connec- 

 tion with the construction of steam-boilers, by the introduction of gus- 

 sets to strengthen the flat ends and retain them in shape. After 

 noticing that all boilers should be of the cylindrical form, Mr. Fair- 



i/ 



bairn observed, that where flat ends are used, they should be com- 

 posed of plates one half thicker than those which form the circumfer- 

 ence. The flues, if two in number, to be made of the same thickness 

 as the exterior shell, and the flat ends to be carefully stayed with gus- 

 sets of triangular plates and angle-iron, connecting them with the 

 circumference and the ends. The use of gussets is earnestly recom- 

 mended, as being infinitely superior to, and more certain in their action 

 than stay-rods. They should be placed in lines diverging from the 

 centre of the boiler, and made as long as the position of the flues and 

 other circumstances will admit. They are of great value in retain- 

 ing the ends in shape, and may safely be relied on as imparting an 

 equality of strength toevery part of the structure. 



COMPARATIVE STRENGTH OF PLAIN AND CORRUGATED METAL. 



SOME experiments have been recently made in Philadelphia, to test 

 the comparative strength of plain and corrugated metal. Two pieces of 

 copper, of equal surface and thickness, were formed into arches of about 



