AND SURFACE CONDENSER. 337 



cold air sides was 565 Ibs. per minute, about one-thirteenth part 

 of the condensing of cold water sides. We never wanted to get 

 the steam above 60 Ibs. to the inch. I have no doubt but that 

 copper pipes of -g.ji\(\. of an inch thick, clean and small, would 

 do considerably more, because the hot water that came out of 

 the boiler from the condensed steam was but 170 degrees, and 

 the external sides the same heat when the steam was 15 Ibs. 

 above the atmosphere in the condensing boiler. This boiler 

 was 4 feet 6 inches diameter, and I think that towards the 

 external sides of the boiler there was a colder atmosphere, if I 

 may call it so, than what it was in the middle of this large 

 condensing boiler, because I found by trying a small tin tube, 

 that it would condense 1500 Ibs. for each foot of cold air sides. 



" However, as it is, it will do exceedingly well for portable 

 purposes. 



" The duty, I doubt not, will be, both for water and air sides 

 condensing, at least 50 per cent, above our Cornish engines, 

 which will be above four times what is now done with ships' 

 engines, especially when you take into consideration their 

 getting steam from salt water, and letting out so much water 

 from the boiler to prevent the salt from accumulating in the 

 boiler, which will make 30 per cent, more in its favour. 



" If strong boilers to stand 200 Ibs. to the inch are made 

 with small tubes, I have no doubt but that the duty would be 

 considerably more, and my engines will not be one-quarter part 

 of the weight, price, or space of others ; and when every advan- 

 tage is taken it will be 1000 per cent, superior in saving of coal 

 to those now at work on board. This engine works well, and 

 returns the steam very regularly every stroke into the boiler. 



" I am extremely sorry you were not present to see these 

 experiments. Please make your remarks on these statements, 

 with any further information you may judge useful. 



" I shall now make drawings agreeable to my experiments 

 for actual performance on board ships. In hope of hearing 

 from you soon, 



" I remain, Sir, 



" Your very humble servant, 



" KICHD. TREVITHICK." 



