Isherwood--The Perkbts Engine. 261 Tile three experiments above referred to, being all that ever were made with steam of the excessive pressure employed and so enormously expandc~, have a peculiar value on account of their fewness and of their greatly exaggerated conditions of pressure and expansion, nothing remotely approaching either bein~ t;mnd in ordinary practice.
Befi)re givin~ the data and results of' the repeated experiment, it is necessary to impress the reader with the thct that the three experiments above referred to, being all made under substantially the same conditions of high pressure and great exl)ansion , have nothing with which they can be properly compared.
The contention of the "Perkins Engine ()ompany " is that the higher the pressure of steam and the more it is expanded, the greater will be the economy. To show this eflhct, one .r many experiments on the same maehinery~ if' all be made under the same eomlitions, are insuflldent. A series is neeessar.v, with varying eomliti.ns, begimfing with the highest pressure and greatest exl>ansion and ~radually reducing botl b ending with the least pressure and expansi,m ,~t' ordinary practice, ascertaining experimentally the results with each reduction ; thus proving or disproving, as the event amy !Je, whether or not the positloll of the "Perkins Engine Company" is well-or ill-tbmided. That Conq)any, however, has not made sm.h exl~eriments; and the two conducted by Mr. Bramwell are incoml>lete in the n.n-aseertainment of the weight of feed-water consumed per hour. h, the one conducted bv the Board of United States Naval En,_,'i,mers. h,,wever, this weight was determined.
As part (,f the economic eflbet (,f "m en,.,'ine, mva,-urcd I)y the cost of the t)ower it develol)s in pounds of e,)al c()nsunw(1 p(,r hour, is due to the quality of the coal, part to the Vpe and proportions of the boiler, and the remainder t-the type "rod prop, wtions of the engineincluding therewith the pressure, quality and expansi,m of the steam used~ it is neressarv to separate these fiwt,,rs and ascertain what portion of the whole eflhet is due to each. Now, in the experilnents made by Mr. Bramwcll~ the finest description of hand-picked N ixon's navigation coal was burned, a coal of exceptional ,tuality for generating steam and of proportionally inere'tsed cost ; and, manifestly, whatever may be the difference in weight of wate,, vaporized in a boiler by rail D" of weight of this coal and by others of very considerably inilerior qualib~ , shouhl not he attrit)uted t. the machinery; so