riN iiti': TiiiioitY or TirK sti;am-i;ngink. 



■i79 



Tiudcr- 



ginning. 



u'th as a 



tii two- 



;ith the 



mil been 



ratios of 



vtbeless. 



to Htatf 



icix'asing 



3h higliei' 



m toward 



engines, 

 lagnitude 

 nitude oi 

 f fuel and 



steam l)y expauHivc workinfr, and it jifTordH a BufRcicnt explanation 

 of the fact, in enginwrinj,' practice, tliut cxpansivo worlcing lias been 

 found to bo t'x[)t'n.sivo vvorixing, and tiiat, in niiiny caHos, an ab.solutoly 

 (.Toater quantity of fuel ha.s been consumed in cxtondod cxpausion work- 

 ing, wliilo less jiowor luis boon dcvolopod.' llo states that liigli speed 

 ruduees tho effect of this cause of loss, and indicates other niothods of 

 cheeking it. He states that ' tho less tho period of admission roiativo to 

 t lie whole stroke, tho grciitir the (piantity of free water existing in tho 

 cylinder.' His cxpcriinents, revealing these facts, were, in some cases, 

 made prior to 1H5'J. JJut the men handling tho engines had observed 

 (liis elfect even before Clark ; he states that they rarely voluntarily 

 adopted ' a suppresnion of al)ove ;iO per cent,,' as they found the loss by 

 condensation greater than the gain by expansion. Describing the method 

 of this loss, this initlior goes on to say that ' to prevent entii'ely tho 

 condensation of steam worked expansively, tin; cylinder must not only 

 he simply protected by the non-conductor — it must bo maiiitained by 

 iiidepcMident (external nu'ans, at the initial temperature of the steam.' 

 Ho thus reiterates the principle expressed by NVatt three-quarters of a 

 century before, and applies it to the nev ly-stated case. 



The same author, writing in 1H77, says : ' Tho only obstacle to the 

 working of steam advantageously to a high degree of (expansion in one 

 cylinder, in genei'al practice, is the condensation to which it is subjected, 

 when it is admitted into tho cylinder at tlie beginning of the stroke, by 

 the le.ss hot surfaces of the cylinder and piston, the proportion of which 

 is increased so that tho economy of steam by expansive working ceases to 

 increase when tlu; period of admission is reduced down to a certain 

 fraction of the strike, and that, on thi' contrary, the ctllcioncy of tho 

 steam is diminished as the period of admission is reduced below that 

 fraction.' Tho niaguitude of this influence may bo understood from the 

 fact that the distinguished engineer Loftus Perkins, using steam of liuO 

 pounds' pressure, and attaining the highest economy kno>vn up to his 

 time, found his engine to consume 102 pounds of fuel per hour per 

 liorse-power ; while this fignre is now reached by engines using steam at 

 one-third that pressure and expanding about tho same amount, and 

 sometimes less. 



Mr. Humphi-ys, writing a little later than Clark, shows the con- 

 rsumption of fuel to increase seriously as the ratio of expansion is increased 

 beyond the vei-y low iigure which constituteil the limit in marine engines 

 of his time. 



Mr. B. F. Isherwood, a chief engineer in tho United States Navy, 

 and later chief of tho Bureau of Steam Engineering, seems to have been 

 tho fir.st to have attem])ted to determine, by systematic experiment, the 

 law of variation cf the amount of cylinder-condensation with variation 

 of the ratio of expansion in unjacketed cylinders. Experimenting on 

 hoard the U.S.S. Michigan, he found tluit the consumption of iuel 

 and of steam was greater when the expansion was carried beyond about 

 one-half stroke than when restricted to lower ratios. He determined the 

 <|uantity of steam u.sed, and the amount condensed, at expansions ra.iging 

 from full stroke to a cut-off' at one tenth. His results permit the deter- 

 mination of the method of variation, with practically satisfactory accu- 

 racy, for the engine upon which the investigation was made, and for 

 others of its class. It was the first of a number of such investigations 

 made by the same hand, and these to-day constitute the principal part of 



pp2 



