SPECIAL REPORT OF MR. HILL, ON MACHINERY. 413
special tubular boilers, containing nearly as much heatiug surface as the main boiler, were placed in the flues. By thus causing the colder water to meet first the coolest gases, they undoubtedly use their heating surface to the best advantage. The writer was unable to learn whether they had had enough experience in this practice to have encountered the difficulty which has made trouble with us ; to wit, the rapid rusting of the heaters containing the cooler water.
As no experiments nor tests were made, little knowledge could be gained of the comparative merits of different systems of boilers. It is suggested here, that should the Philadelphia Exposition include exhibits of working-boilers, as did the Vienna, that it would be advisable that the United States government should detail a number of officers to make thorough experiments therewith.
A large number of engines were to be seen in the Exposition grounds, probably over a hundred and twenty, including marine, winding and blowing engines, portable engines in the Agricultural Hall, and stationary ones, of various types, in the Machinery Building. Some of these were very large. A pair of rolling-mill engines, exhibited by the Prag machinenbau actien gesellshaft, had cylinders 43 by 81 inches, and were calculated for a piston-speed of 850 feet per minute.
An upright compound blowing engine, by the Société Cockerill, of Liege, had a blowing-cylinder 118 inches in diameter by 7 feet 4| inch stroke ; the steam-cylinders being 28.74 and 41.73 inches diameter. This is the one hundred and third engine of its type built by the Company.
A number of steamboat engines were shown, of different sizes, adapted to the coast, river and lake traffic of Europe. With one exception, we believe, these were compound ; that is, after using the steam at high pressure in one cylinder, it is exhausted into another larger cylinder at much lower pressure. These engines were, many of them, for side-wheel boats; and those for this purpose were all, or nearly all, oscillating ; the cylinders being situated perpendicularly, or at an angle under the wheel-shaft. Of the dozen or
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more portable engines, the majority were exhibited by the English, who have a large and flourishing exporting trade