504 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



fixed in one of the packets of the regular service between Marseilles 

 and Algiers. Its principal arrangements were as follows : 



On leaving the cylinder, the steam enters a closed condenser 

 traversed by a series of vertical tubes partly filled with ether. In 

 condensing round these tubes, the steam gives up to them its heat of 

 vaporization and raises their temperature sufficiently to boil the ether 

 they inclose. The vapour of ether, collected in a reservoir above, is 

 admitted from thence into a cylinder where it acts on a piston whose 

 rod is attached to the shaft of the engine. The work of this piston is 

 then added to the work of the other piston, which is moved by 

 steam. 



On leaving the second cylinder the ether vapour passes into a 

 special condenser, also formed of a system of tubes, but these latter 

 are surrounded by a mass of cold water constantly renewed. This 

 vapour thus returns to the liquid state under the influence of the 

 cooling in these tubes, and the ether thence resulting is brought back 

 by a pump moved by the beam into a reservoir situated at the lower 

 part of the tubes of the first condenser. The water of condensation, 

 heated by the excess of heat in the steam, is also itself returned into 

 the boiler. 



The great inflammability of the ether, which, in spite of the 

 greatest precautions, it was impossible to prevent escaping between 

 the joints, rendered these engines dangerous, oh account of possible 

 explosions or conflagrations. Nevertheless they were for a long time 

 tried on the steamboats, Du Tremlley and Le G-cdiUe, as well as 

 in the glass works of the Guillotiere, at Lyons, where an engine of 

 this kind used to work. 



A French naval officer, M. Lafont, substituted chloroform for the 

 ether ; but although the vapour of this substance is not at all inflam- 

 mable, it is asphyxiating, and moreover it was proved by experience 

 that the fittings of the pistons were quickly spoiled by its action. 

 The attempts of which we are speaking were made in Le Galilee 

 engine. Steam has also been employed in combination with the 

 vnpour of sulphur, or of perchloride of carbon. 



Another very interesting engine, which was to be seen at work in 

 the Paris Exhibition of 1867, is the ammonia engine invented by M. 

 Frot, a marine engineer. 



For the water in the boiler M. Frot substitutes a solution of 



