PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 373 



liovcs does not injure the chain, but he deprecates any attempt to make the 

 test mure severe. 



Welding Iron by Hydraulic Pressure. 



Mr. Duportiiil, an eng-ineer in the Western Railway Workshops, Paris, 

 lias succcsst'ully applied hydrauHc pressure for welding of wrought iron. 

 ^Vhen two bars of iron arc brought 1o a welding heat, the pressure is 

 applied continuously, until th(\Y i^ie reduced to the proper thickn(!ss, when 

 the pressure is suspended, and the parts are found to be ftvmly knit together. 

 To test it, one of the halves of the bar was placed under a hammer weigh- 

 ing 1,SU0 kilogrammes — about 3,971 pounds — and not until the third stroke 

 was the welding discovered. 



Mr G. Hartlett expressed doubts whether the welding process is ever 

 completely done. He was informed tliat those targets made of welded iron, 

 tried in the guu experiments a€ Washington, were always fractured at the 

 welded parts. 



Mr. J. K. Fisher said continuous pressure had been often applied — for 

 instance, in the manufacture of large guns. In these instances, however, 

 the hydraulic'press was not applied. It is much better to use a slow and 

 heavy pressure than a series of lighter blows. On small work, however, 

 it is the practice of locomotive works to perform the welding by strokes of 

 the hammer. 



i[r. 1). 1). Parmelee said it was common to weld by means of rollers, and 

 this plan was adopted by Mr. W. K. Marvin, in making his burglar-proof 

 wrotight iron for safes, which consists of emery between fluted plates 

 welded together by rolling. By great pressure the emery is forced into 

 the iron. No drill can penetrate this compound plate. 



The Pneumatic Railway. 



Mr. Secretary' Garvey opened the discussion of the subject by reading 

 the following description, from the London Railway Neios, of a tunnel con- 

 structed in the grounds of the Cr3'stal Palace, rather more than a quarter 

 of a mile in length, and the method of propelling cars through it by atmos- 

 ])heric pressure : 



There is nothing new, of course, in the application of the mechanical 

 action of air to locomotion. The atmospheric system which, in the early 

 days of the railways, was adopted at Croydon, on the South Devon Railway, 

 at Dalkey and other places, was founded upon well established laws of 

 pneumatics, and it failed only in consequence of practical diflSculties in the 

 way of carrying it out. 



A second step in the development of the atmospheric sj'stem is that 

 which has Ijeen carried out by the Pneumatic Dispatch Company, and by 

 which the mail bags are daily dispatched from the N. W. District Post 

 Office to the Euston Station; but it remained to be shown by actual experi- 

 ' ment that the principle may be most successfully applied f(jr passenger 

 traffic. 



In the old atmospheric system the train of carriages was propelled by 

 the ordinary pressure of atmospheric air acting upon a piston moving in a 

 tube, the air before it being more or less exhausted. The tube was, how- 



I 



