20 ENGINE TESTS. 



the lazy-tongs, and moving on guides attached to the cylinder, 

 the direction of motion being parallel to it. A screw fastened 

 to the rod at the proper place serves to carry the motion to the 

 cord attached to the indicator. The use of the rod in place of 

 the cords is especially applicable to tandem engines. 



For high-speed engines the driving apparatus is some form 

 of lever and sector, the shaft on which the lever is mounted 

 being in many cases supported by a stand bolted to the frame 

 of the engine. In some engines of the high-speed compound 

 class the driving motion is derived from an eccentric fastened 

 to the main shaft, the motion being carried from this point to 

 the cylinder through a connecting-rod and bell-crank lever. In 

 these cases an independent motion is used for each cylinder. 



It has been the custom in making these tests to employ two 

 indicators for each cylinder, attached as close as possible to the 

 end of the cylinder, using the half-inch connection, a right-angle 

 elbow, and the indicator-cock furnished with the instrument. 

 Sometimes a straight-way valve is placed below the indicator- 

 cock for facility in moving the same without shutting down 

 the engine. The objections to long pipes connected by a three- 

 way cock in the center, consist in the increased friction of the 

 steam in passing through the greater length of the pipe with 

 the increased number of bends, and in the collection of water 

 in the long horizontal cavity which is thus brought into play. 

 If two indicators are not available for an engine test, it seems 

 better to use one instrument, and transfer it from one end to 

 the other, than to employ the three-way cock and have the 

 instrument fixed at the central point with the long connections. 



On many of these tests " prepared " indicator paper has been 

 used, the instrument being fitted with metallic marking-points. 

 These marking-points are made of brass wire of suitable size, 

 which is reduced in diameter near the marking end to about 

 sV, so that by the use of a small hand-vise, such as watch- 

 makers employ, and an oil-stone, the marking-point is readily 

 kept in shape for tracing fine lines. The use of metallic paper 

 is much to be preferred, as a matter of convenience, to plain 

 sheets with the ordinary lead-pencil point, inasmuch as the 



