. American ENGINEER and Railroad journal . y plus grande efficacité que ceux avec les plus petits, et si cela être ainsi le diagramme est justifié. Les variations dans allprobabilité doivent être regardées dans la chambre de combustion, et ce, je pense, ex-plaines les résultats particulièrement bons obtenus de 3000 à des taux élevés. Le tir, bien que uniformément excellent, a été indubitablement gouvernée quelque peu par les demandes sur lui. Quand le bobinern'était pas tellement pressé, l'épaisseur du feu n'était pas al-voies le meilleur, conduisant à l'excès d'air ou la faute opposée, la formation de CO, et ceci à son tour exercé une influence sur les theresults tha

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. American engineer and railroad journal . y greater efficiency than those with the smaller, and ifthis be so the diagram is justified. The variations must in allprobability be looked for in the firebox, and this, I think, ex-plains the specially good results obtained from 3000 at highrates. The firing, while uniformly excellent, was undoubtedlygoverned somewhat by the demands on it. When the boilerwas not so much pressed, the thickness of the fire was not al-ways the best, leading to excess of air or the opposite fault, formation of CO, and this in turn exercised an influence on theresults that is almost impossible to accurately measure. Thelow results of 734 can, of course, be explained by its being anarrow firebox engine, and as for 929 it must be rememberedthat this engine was never worked to anything like the capacityof its boiler, and it showed a very high percentage of CO, con-sidering the coal burnt per square foot of grate. It does notseem justifiable from the results obtained from this engine to 111111 j! 1:! 11 i 1MI. dispute the general agreement of the other tests, and it there-fore appears safe to consider that the curve drawn representsvery closely the evaporation results that will be obtained froma boiler with first-class firing and average conditions otherwise. It will, perhaps, be as well to take this opportunity to referto a paper which I read some three years ago on the questionof heating surface, and in which I now believe I drew someentirely erroneous conclusions. The value of heating surfacewas shown to be proportional to the square root of the lengthof the tubes, in place of their length. In one sense this is true.For instance, if with 1, 000 feet of heating surface coal was burntat the rate of 2, 000 lbs. per hour the evaporation would, by Fig.I, be 7 lbs. If the heating surface were doubled the evaporationwould be 9.3 lbs., or 1.33 times as great. Now, as the squareroots of 1000 and 2000 are in the proportion of 1.41 to 1.00, there was sufficie

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