170 APPENDIX. 



described ; the lathe was then applied to turn a case-hardened roller for rolling boiler plates, 

 and the pencil traced the figure E. The merchant-bar rolls were now set in motion, in 

 addition to the above (these rolls are for making the ordinary square and round bar iron), but 

 they were not employed in rolling it : the additional power required to keep them going 

 increased the figure to F. The puddled ball rolls, the small rolls, the heavy lathe, and the 

 shears were kept in full work, and the engine being fully loaded, the figure G was delineated. 

 The diagram shows that the engine was doing its duty, and it was proved that an engine 

 of larger power must be employed if the merchant rolls and the plate rolls be required to be 

 kept in work, rolling iron at the same time with the other machinery. During this experiment 

 the safety valve of the boiler was loaded at 3 ffis. upon the square inch above the pressure 

 of the atmosphere ; and it will be seen by the diagram, which is an exact copy of that actually 

 made by the instrument, what mechanical force was taken in each case, and at each point of 

 the piston's course. It has been noticed that the stroke was 7 feet ; the steam was cut off 

 about 9 inches from the end of the stroke, as the diagram shows ; and the action of the 

 governor may be discerned, as regulating the supply of steam, a little farther from the cylinder 

 top every time the engine's load is increased. The effective or disposable force of the engine 

 will be found to be about 10 tfes. on each square inch of the piston, the area of which is 

 101 7'8 inches, which makes the actual power of the engine about 69 horses, reckoning 33,000 

 ffis. raised one foot high in a minute each horse power ; whereas, the nominal power of the 

 engine was only 55 horses, as indeed it would be called by most of the engine-makers. 



