Prime Movers. 



19 



formed "by liquified carbonic acid from 32° to 86° Fahrenheit, 

 amounts to from thirty- six to seventy-three atmospheres ; and 

 the volume from twenty to twenty-nine — the expansion being 

 four times that of atmospheric air. But Davy did not remark 

 that the space through which the pressure is exerted is incon- 

 siderable. The less the specific gravity of a vapour, compared 

 with that of the fluid from which it is produced, the more 

 effective it will be as a mechanical agent ; but the specific gra- 

 vity of steam is less than that of any vapour which has been 

 tried, not only when compared with liquids, such as alcohol, 

 etc., but with liquified gases also ; as will appear from the 

 following : — 



Liquids. 



Spec. Grav. 

 of Vapour. 



Spec. Grav. 

 of Liquid. 



Temperature. 



i. ■— 



Mechanical 

 Eifect. 



Sulphurous Acid 



2-777 



1-192 



1-818 



05962 



2-496 



0-48 



1-42 



09 



0-9 



0-76 



1-33 



1-000 



45° 

 50" 

 45" 

 50" 

 50" 

 212" 



426 

 630 

 395 



1057 

 440 



1711 













The gas engine was intended, by Brunei, to apply to 

 practical purposes the power expected from the expansion of 

 liquified gases ; and it must be a source of wonder and regret, 

 that so enlightened a man should have wasted his ingenuity on 

 so hopeless a project. He placed liquified carbonic acid in two 

 receivers ; and when these were heated and cooled alternately, 

 the resulting expansions and contractions were made to com- 

 municate motion to a piston, working in a cylinder, which was 

 placed in an intermediate position. A rise of 180° gave a 

 pressure of ninety atmospheres ; which, having no resistance to 

 overcome, except that of the vapour in the other receiver, at a 

 lower temperature, tended to move the piston with a force 

 estimated at sixty atmospheres. The pressure was undoubtedly 

 very great ; but the distance through which it acted was trifling. 

 Brunei constructed an eight-horse engine on this principle. 



It was hoped that a boiler, furnace, and all their attendant 

 inconveniences would be rendered unnecessary, by using ex- 

 plosive gases instead of steam, for the production of a vacuum ; 

 and the gas vacuum engine was patented for this purpose in 1824. 

 The air was rarefied alternately in two chambers, by burning 

 coal gas within them; water, which was then forced up by 

 atmospheric pressure, was used to turn an overshot wheel. 

 The inventor proposed applying this principle to the movement 

 of a piston in a cylinder ; but the contrivance would then be 



