448 
The Chairman, alluding to the opinion entertained by 
some, that the consumption of smoke was only a questionable 
benefit, as the increased generation of carbonic acid gas 
neutralised the apparent benefit, said he believed that there 
was as much carbonic acid gas evolved where the smoke was 
not consumed, as where it was. 
Mr. Ward made some observations with reference to the 
chemical process of combustion, and expressed his opinion 
that this apparatus was fully adapted to all the requirements 
of the case. As to carbonic acid gas, the public were under 
a complete mistake as to its being a deleterious gas. It was 
entirely neutral in its operations when pure, and from 20 to 
25 per cent, in the atmosphere might be breathed without 
injury ; but one per cent, of carbonic oxide would be extremely 
poisonous, and the latter was often confounded with the 
former. As to vegetation, carbonic acid gas was a benefit, 
but they did not find their vegetation improved by smoke 
from long chimneys, and the question arose as to whether the 
gas evolved was not carbonic oxide. He did not, however, 
apprehend much detriment from carbonic oxide, as its specific 
gravity was such that it would rise into the atmosphere rather 
than descend. 
The Chairman said that the injury to vegetation did not 
arise from carbonic acid or carbonic oxide, but from the 
sulphurous gases, which could not be got rid of. 
Mr. Ward expressed his dissent from this view, and said 
he believed the injury to the plants arose from the deposit of 
solid carbon, which stopped the pores of the leaves. As to 
the mechanical part of the question, he thought there was no 
danger from the bursting of the tubes, as tubes of locomotives 
were continually bursting without any material injury result- 
ing. He thought if there was any weakness, it was in the 
absence of sufficient stays in the fire box, according to the 
sections on the patentees' circular. 
