337. As an example of the difference in the results obtained by different authors, take the following:—
An engine to do the same work must have, according to
| Zerah Colburn.[[6]] | Norris.[[7]] | D. K. Clark.[[8]] | D. K. Clark.[[9]] | |
|---|---|---|---|---|
| 18 × 22 | 18 × 22 | 18 × 22 | 18 × 22 | Cylinders. |
| 5 | 5 | 5 | 5 | Wheels. |
| 13.00 | 13.86 | 14.00 | 19.60 | Grate area. |
| 1114 | 812 | 1327 | 1327 | Heating surface. |
| 250 | 324 | 134 | 134 | Area of chimney. |
| 4 | 23 | 28 | 28 | Area of blast. |
| 59 | 73 | Steam room. | ||
| 100 | 73 | Water room. |
[6]. Colburn on the Locomotive Engine.
[7]. Norris’s Handbook for Locomotive Engineers and Machinists.
[8]. D. K. Clark’s Railway Machinery, calculated for coke.
[9]. D. K. Clark’s Railway Machinery, calculated for wood.
From these figures, the work done being the same, Mr. Clark gives forty per cent, more grate area than either Colburn or Norris, an easier blast, and greater heating surface. Norris makes the steam and water room equal, while Colburn makes the latter almost double the former. It is to be observed that Colburn gives only rules adopted by different builders, not vouching for their correctness, while Norris lays down his rules as fixed and right. The engines used by the English experimenters in their observations, vary in dimension between the following wide limits, whence the universal application of their results.
| Grate area | 9 to | 24 | square feet. |
| Fire surface | 50 to | 100 | square feet. |
| Tube surface | 400 to | 1,000 | square feet. |
| Whole surface | 450 to | 1,100 | square feet. |
| Blast orifice | 10 to | 20 | sq. inches, area. |
| Speed of engine | 12 to | 20 | miles per hour. |
338. The result of some sixty experiments upon forty-five different engines (detailed in Clark’s Railway Machinery, page 156), gives the following formula, expressing the relations which ought to exist between grate area, heating surface, and consumption of water; that evaporation may be carried on in the most economical manner.