234 Dr Fyfe on (he Illuminating and Heating "Power of 



of 35. When the same flame was put under the boiler already 

 described, the same quantity of water was raised to 110, giving 

 a gain of ^^. With other burners the results were similar, 

 the heat communicated to the boiler being nearly double o'f 

 that acquired by the common pot. 



There is another circumstance of material consequence to be 

 attended to. When gas is burned, watery vapour is formed 

 by the union of the oxygen of the air with the hydrogen in the 

 gas. As long as this is kept warm by the products of com- 

 bustion, it is retained in the aeriform state, but if by any 

 means the products of combustion are cooled, then the watery 

 vapour is condensed, and gives forth its latent heat; and 

 hence the increased effect, when the boiler already described 

 was used, is not owing merely to the retention of the heat that 

 otherwise would have been lost by radiation, but also to the 

 products of combustion being so much cooled, as to cause the 

 condensation of part of the vapour generated. In using this 

 apparatus, the air from the tube passing through the water, 

 escaped at a temperature varying from 120 to 130, according 

 to the kind of burner and the quantity of gas used ; the more 

 rapidly the gas was burned, the higher was the temperature 

 of the air from the escape tube. It is evident then, that, even 

 in this way of applying the heat, much of it was lost ; and 

 hence it appeared, that, by transmitting this heated air and 

 steam also through the fluid, there would be a still farther in- 

 crease of temperature, provided the draught could be kept up, 

 so as to carry off the products of combustion. 



To put this to the test, I had another vessel adapted to the 

 boiler ; it was merely a tin trough capable of holding half a 

 gallon, through which there was passed a tube that fitted on 

 to the escape tube of the boiler. 



When the gas was consumed under the boiler in this way, 

 the boiler containing one gallon, and the other part of the ap- 

 paratus half a gallon, at 45, by the combustion of 1^ foot of 

 gas, the temperature of the water, when mixed, was 118. The 

 air, as it escaped from the tube, was 70, that of the atmo- 

 sphere of the room being 58. By adapting another vessel of 

 a similar nature to the preceding, and also containing half a 

 gallon of water, the temperature was still farther elevateds 



