34 



NOTES ON STATIONARY ENGINES. 



about what is known as " black-rod." Whilst, however, the 

 material has been loss reliable, it has been found to be 

 necessary to drill all holes in plates exposed to tension ; this 

 is found to bo attended with many advantages, and witlial at 

 such a low cost, that the universal practice of punching, 

 which was followed with iron, and which is now possible 

 with steel, will proha,bly never be rovoi'ted to on a large 

 scale. 



All boilers should be fed with water which has passed 

 through some kind of feed heater, as by this means straining 

 of the plates owing to dKTorenecs in tenipei'ature are avoided. 

 Any feed heater which is used so as to take advantage of tlie 

 waste heat in the chimney gases, or in the exhaust of a non- 

 condensing engine, introduces an clement of ecoriomy wliieli 

 is of importance; but another advantage is also secured iu 

 the fact that with almost all descriptions of water much 

 solid matter is precipitated in the heater, and therefore 

 before its entry into the boiler. There is, however, a grea-t 

 probability that before \erj long some sort of apparatus for 

 the purpose of water purification or softening will come into 

 extensive use. If this should be the case, there will bo in 

 all good practice two separate appliances brought to bear 

 upon the water before its entry into the boiler, the first for 

 the removal of impurities, and the second one for a ])re- 

 liminary raising of the temperature. 



A boiler of the ordinary class, with two furnaces, each 

 2 feet 9 inches wide, and a good chimney, will easily burn 

 twenty tons of coal per week's work of fifly-foui' hoiii-s, and 

 evaporate 160 to 200 tons of water in the same time. Mac- 

 farlano Gray's a,pproximate rule for marine boilers, is that 

 one ton of coal is consumed per foot in widtli of tlie grate 

 per twenty-four hours, irrespective of the length, from front 

 to back ; the above figures for a land boiler give about half as 



