175 
Steam Engine. 
part of the cylinder in the improved engines first brought 
into effect by Messrs. Boulton and Watt ; that this ratio is 
progressive, and nearly if not entirely uniform, so that steam 
of the expansive force of 20, 30, 40, or 50 pounds the 
square inch of a common safety-valve will expand itself 
to 20, 30, 40, or 50 times its volume ; and that, general- 
ly, as to ail the intermediate or higher degrees of elastic 
force, the number of times which steam of any tempera- 
ture and force can expand itself, is nearly the same as the 
number of pounds it is able to sustain on a square inch 
exposed to the common atmospheric pressure : provided 
always that the space, place, or vessel in which it is allowed 
to expand itself, be of the same temperature as that of 
the steam before it be allowed room to expand. 
Respecting the different degrees of temperature required 
tb bring steam to, and maintain it at, different expansive 
forces above the weight of the atmosphere, Mr. Woolf 
has found, by actual experiment, setting out from the 
boiling point of water, or 212*^, at which degree steam of 
water is only equal to the pressure of the atmosphere, that 
in order to give it an increased elastic force equal to five 
pounds the square inch, the temperature must be raised to 
about 227“'^, when it will have acquired a power to ex- 
pand itself to five times its volume, still be equal to the at- 
mosphere, and capable of being applied as such in the 
working of steam engines, according to his invention : 
and with regard to various other pressures, temperatures, 
and expansive forces of steam, the same are shown in the 
table which he has inserted in the following specification : 
Specification of the Patent granted to Arthur Woolf, of 
Spa Fields, in the County of Middlesex, for certain Im^ 
provements in the Construction of Steam-Engines. 
Dated June 7, 1804. 
To all to whom these presents shall come, &c. Now 
know’ ye, that in compliance with, the said pro^uso, I tlie 
