M E C H . 
the fquare inch, can expand to fix, feven, eight, nine, or 
ten, times their volume, and (till be refpeClively equal to 
the atmofphere, or capable of producing a fufficient aCtion 
sgainft the pilton of a (team-engine to caufe the fame to rife 
in the old engine (with a counterpoife) of Newcomen, or 
to be carried into the vacuous part of the cylinder in the 
intproved engines firft brought into effect by Meffrs. Boul¬ 
ton and Watt; that this ratio is progreflive, and nearly if 
not entirely uniform, fo that (team of the expanfive force 
of twenty, thirty, forty, or fifty, pounds the fquare inch 
of a common fafety-valve, will expand itfelf to twenty, 
thirty, forty, or fifty, times its volume ; and that, gene¬ 
rally, as to all the intermediate or higher degrees of elaltic 
force, the number of times which (team of any tempera¬ 
ture and force can expand itfelf is nearly the fame as the 
number of pounds it is able to fuliain on a fquare inch 
expofed to the common atmofpheric prelfure; provided 
always that the fpace, place, or veffel, in which it is al¬ 
lowed to expand itfelf, be of the fame temperature as that 
of the (team before it be allowed room to expand. 
RefpeCting the different degrees of temperature re¬ 
quired to bring (team to, and maintain it at, different ex¬ 
panfive forces above the weight of the atmofphere, Mr. 
Woolf has found, by aCtual experiment, fetting out from 
the boiling-point of water, or 2.12 0 , at which degree (team 
of water is only equal to the prelfure of the atmofphere, 
that, in order to give it an increafed elaftic force equal to 
five pounds the fquare inch, the temperature mud be 
raifed to about 127I, when it will have acquired a power 
to expand itfelf to five times its volume, (till be equal in 
prelfure to the atmofphere, and capable of being applied as 
fuch in the working of fteam-engines according to his in¬ 
vention ; and, with regard to various other preffures, tem¬ 
peratures, and expanfive forces, of (team, Mr. Woolf 
has formed them into a table, for which, and fome other 
minute particulars of the firft patent, we refer to Gregory’s 
Mechanics, vol. ii. Mr. Woolf, in his fpecificatipn, de- 
fcribes various modifications of his invention, and points 
out means for applying his improvements to the working 
of fteam-engines already in ufe. Suffice it to fay, that, 
proper means being employed to keep the ftearn-veffel or 
working cylinder at the required temperature, the (learn 
is admitted into it in quantities proportioned to its ex¬ 
panfive power 5 for example, if the (team be of a force 
equal to forty pounds the fquare inch, the throatle-valve 
is fo adjufted as to admit into the working cylinder a 
quantity of fleam equal to only one-fortieth part of its 
capacity, which fleam expands as it enters, fo as to fill 
completely the whole cylinder. In this firft improvement 
of Mr. Woolf, though the faving of fuel might be car¬ 
ried to a confiderable length, (and, with an engine ereCted 
by Meffrs. Murray and Cay, of Leeds, has actually been 
proved to be more than one-half of the whole quantity 
employed in a well-conftruCted double engine of the fame 
power,) it was flill neceffarily limited by the ftrength of 
materials; for in the employment of high fleam, there 
rnuft always be fome danger of an explofion. Mr. Woolf, 
however, by a happy thought, has obviated every danger 
of this kind, and can now take the full advantage of the 
expanfive principle without the leaft danger. This he 
effects by throwing into common fleam the additional 
temperature neceifary for its high expanfion, after the 
fleam is admitted into the working-cylinder, which is 
heated by means adequate to the end intended to be ob¬ 
tained ; and the advantage which he thus gains, he ef¬ 
fectually fecures by a molt ingenious improvement in the 
pifton. It may be eafily conceived that (team of fuch high 
rarity as Mr. Woolf employs, could not be made fully ef¬ 
fective with the pifton in common ufe ; for, in propor¬ 
tion to its rarity, fo mull be the facility with which a por¬ 
tion of it would efcape, and pafs by the fide of the pifton 
to the vacuous part of the cylinder; but Mr. Woolf’s 
contrivance, which confifts in employing upon the pifton 
a column of mercury or other metals in a (tate of fufion 
©f an altitude equal to the preflure of the fleam, feems per- 
Vot.XIV. No. 1013. 
I N I C S. 7 B5 
feCtly adapted to prevent the lofs of even the fmalleft por¬ 
tion of the fleam. Befides thefe improvements on the 
common fleam-engine, he has alfo found means to apply 
the fame principles to the old engine, known by tire name 
of Savery’s, in fuch a way as to render the fame a power¬ 
ful and economical engine for a great variety of purpofes. 
There leems, indeed, to be a reafonable ground to hope 
that a great defideratum, a real faving of fuel, will be ef¬ 
fected by Mi;. Woolf’s improvement, founded on his dif~ 
covery of the ratio in which fleam of any high temperature 
can expand itfelf. It is certainly a new and curious faCt, 
that fleam may, by mere additions of temperature, be in¬ 
creafed in volume in the way he ftates, and (till be equal 
in force to the common atmofphere. The advantage 
which he gains, or, in other words, the faving which he 
effeCts in the quantity of- fuel, depends entirely on the 
correCtnefs of this fact; for, according to the ideas hi¬ 
therto entertained, fleam of the ftrength of about thirty 
pounds the inch, above the common atmofphere, ought 
only to effeCt the work of two atmofpheres more than 
fleam of 212 0 ; but according to Mr. Woolf, by proper 
management, it may be made to produce the work of thirty 
atmofpheres ! 
Mr. Woolf’s fecond patent is dated June 1810. In this 
laft machine, the working-cylinder has no bottom, but is 
enclofed in another cylinder of fuch dimenfions, that the 
fpace between the two is equal, at leaft, to the contents 
of the working-cylinder. The lower rim of the working- 
cylinder is about the fame diftance from the bottom of the 
enclofing cylinder as the Tides of the two cylinders are 
apart. A veffel of any other fhape, as well as a cylinder, 
will do to enclofe the working-cylinder; and even a de¬ 
tached veffel, communicating with the working-cylinder 
at the lower part, will anfwer the lame purpole, though 
the patentee prefers the arrangements defcribed. Into the 
enclofing-cylinder fuch a quantity of oil or fat is put, as 
(hall, when the pifton is at its greateft height in the work¬ 
ing-cylinder, fill all the fpace beneath it, and alfo fill the 
enclofing-veffel to the height of a few inches above the 
lower rim of the working-cylinder. A few inches in height 
of oil are alfo poured in above the pifton. If the engine 
is to be open to the atmofphere, the enclofing-veffel has a 
communication with the boiler above, which, when opened, 
caufes the oil or fat to afcend beneath the pifton as it rifes ; 
and when the paffage to the boiler is clofed, and that to 
the condenfer opened, the prelfure of the atmofphere forces 
the oil back again into the enclofing-veffel. In a clofed 
or double engine, the communications from the boiler and 
condenfer are to be to the top of the working-cylinder, 
and to the top of the enclofing-veffel. Means are to be 
provided by cocks, or valves, and a fpring-pump, to keep 
the oil at a due height over the pifton, if it (liould be 
found to diminifh. By thus interpofing oil between the 
pifton and the lteam, both above and beneath, all wade of 
fteam, by its paffing the pifton, is effectually prevented, 
and a confequent faving of fuel effected. The patentee 
adds, that, though he defcribed the pifton of his engine 
as working in a cylinder, in the ufual way, it may alfo be 
made to work in a four-fided or other polygonal prifmatic- 
formed veffel. 
This method feems well calculated to effeCt the objeCt 
in view ; for, unlefs the fluffing of the pifton be very 
loofe indeed, neither (team nor oil can eafily pafs it. At 
the fame time we muft obferve, that the part of the me¬ 
thod which relates to fecuring the upper part of the pifton, 
by having a quantity of oil poured in above it, has been 
long praCtifed in other engines, and appears in itfelf fo ef¬ 
fectual, that the addition made by Mr. Woolf, of fecuring 
the lower part of the pilton by oil alfo, feems fcarecly ne- 
ceffary. It (hould be noticed, that Mr. Woolf’s method 
is only applicable to low-preffure engines ; for, in thofe 
of high prelfure, where the heal of the fteam mult be 
great, not only fo great an evaporation of the oil would 
be caufed as muft add much to the expenfe, but there 
would alfo be fome rifle of the production of inflammable 
9 O vapours. 
