THE STEAM-ENGINE. 151 



by formulae shows how you may vary the proportion accord- 

 ing to the amount and to the temperature of the water pumped 

 past the cooling surfaces. 



The before-mentioned condensers, whether injection or 

 surface, require a large amount of water, but there is another 

 kind of condenser not much used, but which should be a 

 great deal more used than it is, for the purpose of surface 

 condensing, a condenser by means of which you can, wher- 

 ever you have sufficient water to feed a boiler, efficiently 

 condense the steam of the engine. This condenser consists 

 of a number of rows of horizontal tubes connected at the 

 ends to vertical stand-pipes. Over the topmost of these rows 

 there are troughs, perforated, into which the condensing water 

 is pumped, and from which it trickles over the surface of the 

 condenser and thereby condenses the steam, there being 

 evaporated from the outside of the condenser in the form of 

 mist or reek almost exactly the same weight of water as 

 was used for the feed. The condensing water that is not 

 evaporated is collected at the bottom and is repumped in a 

 warm state on to the top of the condenser, and by that 

 apparatus it is, as I have said, perfectly practicable to main- 

 tain a very excellent vacuum of some twenty-four or twenty- 

 six inches by an expenditure of no more water than that 

 which of necessity must be expended in the feed of a non- 

 condensing engine. 



Besides that we have had condensation effected by means 

 of the air. A good many years ago a gentleman of the name 

 of Craddock invented an air condenser which consisted of 

 a cage placed on the roof of the engine-house and joined 

 by a stuffing-box to the eduction-pipe. This case was caused 

 to revolve in the air, and the contact of the air with the 

 surface effected condensation. I have not the particulars, 

 and I do not think the vacuum obtained was very good, 

 but nevertheless there was a vacuum obtained, and the con- 

 denser was put to work at the London works, Birmingham, 

 then the property of Messrs. Fox, Henderson, and Co. 

 Then for the purpose of bringing the steam back into water 

 to be used over again we have the air condenser of Hancock, 

 who, in his engines, had the condenser made on the same plan 

 as his boiler, through the condenser the air was blown, and 

 that air afterwards fed the fire. 



There are very many benefits attending the use of surface 



