68 Royal Society : — Mr. 0. Reynolds on the Condensation 



its efficiency : this is particularly important with reference to the 

 swf ace-condenser. 



Second. If air prevents the condensation of steam, then by send- 

 ing air into the boiler of a high-pressure engine, the condensation 

 at the surface of the cylinder will be prevented, which, if allowed 

 to occur, becomes a source of great waste ; for when the steam 

 comes into a cold cylinder it condenses, heating the cylinder and 

 leaving water, which will again be evaporated as soon as the steam 

 escapes ; and this, in evaporating, will cool the cylinder. By pre- 

 venting this, the mixing of air with the steam would effect the same 

 object as the steam-jacket, only in a more efficient manner ; for the 

 heat communicated to the steam in the cylinder from the jacket is 

 not nearly so effective as that which is communicated from the 

 boiler, in consequence of the steam in the cylinder being at a lower 

 temperature than that in the boiler. 



. 3. The experiments for this investigation were, by the kind per- 

 mission of Dr. Roscoe, carried out by Mr. Pasley, a student in the 

 Chemical Laboratory of the Owens College ; and I beg to tender 

 him my best thanks. 



4. In making these experiments two objects were particularly 

 kept in view : — 



First. To ascertain if there is a great difference in the rate of 

 condensation of pure steam and a mixture of steam and air — to 

 ascertain in fact whether pure steam condenses at an unlimited 

 speed. 



Second. To ascertain if (and according to what law) the effect of 

 air on the condensation increases as the proportion of air to steam 

 increases. 



5. Of these two undertakings the first is much the most difficult. 

 The rate of condensation of pure steam is so great that it is prac- 

 tically impossible to measure it ; and to institute a comparison be- 

 tween this and the condensation of a mixture of steam and air is 

 like comparing the infinite with the finite. It is practically impos- 

 sible to keep any surface cold when an unlimited supply of pure 

 steam is condensed upon it, so that under such circumstances the 

 quantity of pure steam condensed is limited by the power of the 

 surface to carry off the heat. The best method of obtaining a 

 quantitative result seems to be by introducing sufficient cold water 

 into a flask of steam to condense it all, and ascertain whether this 

 condensation is effected suddenly or slowly. 



6. The presence of hot water in the flask with the steam very 

 much assists in ascertaining the rapidity of condensation. When 

 there is no hot water in the flask, the condensation by the injected 

 water is only a question of time ; the gauge will come to the same 

 point whether the condensation is quick or slow, the only differ- 

 ence being in the speed at which it will rise — a difference not easy 

 to appreciate, especially when the motion is quick. But if hot 

 water is present, then as the steam in the flask is condensed it is 

 replaced by fresh steam from the water, and the interval between 

 the condensation and the consequent ebullition is the only time 



