84 Report of Judges on Portable Steam- Engines at Cardiff. 
diately above tlie bars burns it, and forms carbonic acid ; but this 
carbonic acid, in passing up through the layer of fuel above, 
dissolves, as it were, that fuel, and takes out of it an equivalent 
of carbon, so as to bring this carbonic acid back to the state of 
carbonic oxide, a highly combustible gas. But if this carbonic, 
oxide cannot obtain air above the fire, it goes away unconsumed ; 
and when it is considered that a pound of carbon, which would 
evolve 14,000 units of heat, if it were all turned inlo carbonic 
acid, will only evolve 4000 units of heat if the carbonic oxide 
stage alone be reached, it will be seen how necessary it is to 
effect the perfect combustion of the fuel. On the other hand, 
if, with the view of ensuring this, an excess of air be admitted 
through the fire, that air has to be heated from the temperatures 
of the atmosphere to that at which it enters the chimney, and 
this heat is all so much waste. These considerations show the 
great importance of having the most perfect regularity of fire. 
During the trials, this regularity is obtained by the employment 
of men who exhibit the highest skill and diligence in attending 
to the firing. In order to preserve uniformity, they fire from. 
. thirty to forty-five times in the hour, but clearly in practice no 
man could so attend to a fire ; he would be worn out with the 
labour, and even if he could endure the toil, the user of the 
engine could not afford that a man's time should be exclusively 
occupied in this way ; and thus, however high the results may 
be that are developed by a boiler on trial, these results must fall 
off in actual work. But if agricultural engineers would turn 
their attention to devising some simple kind of mechanical firing, 
by which uniformity of distribution should be ensured, it is 
believed that the most beneficial results would follow, and that 
in the practical use of the engine, a very high evaporative duty 
would be at all times maintained, while the engine-driver would, 
be left at liberty to attend to other work. 
In concluding this Report, the Judges are happy to be again 
able to thank all the Exhibitors for the cheerful manner in 
which they attended to the Judges' wishes ; and they have also 
to thank the Stewards for their courteous and valuable aid and 
assistance. 
(Signed) F. J. Bramwell, 37, Great George Street, Westminster. 
W. Menelaus, Duiolais. 
