472 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



glass, is employed to form it into cakes, which are compressed 

 and dried at a gentle heat. Special apparatus has been de- 

 vised for its combustion. 5 (7, xxxix., 311. 



CONDENSATION OP STEAM BY COLD SURFACES. 



An investigation by Reynolds, Professor of Engineering in 

 Owen's College, Manchester, on the condensation of a mixt- 

 ure of air and steam upon cold surfaces, has important prac- 

 tical bearings in the management of the steam-engine. His 

 objects were to ascertain if there is a great difference in the 

 rates of condensation of pure steam and a mixture of steam 

 and air; and, again, to ascertain if the effect of the mixed air 

 on the condensation increases as the proportion of air to 

 steam increases. The rate of condensation of pure steam is 

 so great, when it impinges upon a cold surface, that it is prac- 

 tically impossible to measure it ; wherefore indirect methods 

 of investigation were necessary. The conclusions drawn 

 from his experiments are as follows : First, that a small quan- 

 tity of air in steam does very much retard its condensation 

 upon a cold surface ; that, in fact, there is no limit to the rate 

 at which pure steam will condense, except the power of the 

 surface to carry off the heat. Second, that the rate of con- 

 densation diminishes rapidly, and nearly uniformly, as the air 

 that is present increases in a proportion of from two to ten 

 per cent, of the steam, and then less and less rapidly until 30 

 per cent, is reached, after which the rate of condensation re- 

 mains nearly constant. Third, that, in consequence of this ef- 

 fect of air, the necessary area of surface of a condenser for a 

 steam-engine increases very rapidly with the quantity of air 

 allowed to be present within it. Fourth, that by mixing air 

 with the steam before it is used the condensation at the sur- 

 face of the cylinder may be greatly diminished, and conse- 

 quently the efficiency of the engine increased. Fifth, that 

 the maximum effect, or nearly so, will be obtained when the 

 pressure of the air is one tenth that of the steam. Proc. Roy. 1 

 ^oc, 1873, 280. 



SIMPLEST STEAM-MOTOR. 



The solution of the problem how to utilize the expansive 

 force of steam in the simplest manner, so as to produce a con- 

 tinuous rotary motion, is furnished by an invention of Pro- 



