Steam:
Its Generation and Use

CENTENNIAL BOILER TESTS. At the U. S. Centennial Exposition held in Philadelphia in 1876, a careful test was made of the different boilers there exhibited, except the Corliss, which was not placed in competition. The results of these tests have been condensed in the following diagram, which gives graphically not only the relative evaporation, but the rate of combustion of coal per square foot of grate, the ratio of heating to grate surface, the water evap- orated per square foot of heating surface, and the waste heat in the flue. The height of the diagram is 105 millimeters, and represents the to difference in the construction of the boilers, by which the heating surface was rendered more effective. The fact that the best economic re- sults were obtained by a boiler under average conditions in other respects, is significant. In their report, the Judges said : “ 1 he awards of the Judges were not based upon the trials ; in fact, the latter were not commenced until the awards had been made by another committee of the same group. This report has been confined to a statement of what actually took place during the trials, without expressing opinions on the all- important question of value, but more particu- theoretic value of the combustible used in the experiments. In the line of economy the boilers are arranged in the order of their relative economy, as shown in the tabic. I he distance of this line from the base, relative to the whole height, gives the percentage of useful effect in each case. All the lines have scales measured in millimeters, from a common base. By reference to the lines of averages, it will be seen that boilers at the extremes of economy, had an average of each of the conditions. The different results are, therefore, to be attributed larly the trustworthiness of the different mechani- cal details and arrangements employed by the various exhibitors. Many of these questions can only be settled by long practical use, under dif- ferent circumstances as to management and the kind of fuel and water used.” In view of that statement it is an interesting fact, that of all the fifteen boilers tested at the Centennial, only three can be said to be now fairly in the market, and of these, the Babcock & Wilcox, which showed the best results there, is the only one extensively sold in this country. 85