192 ON THE EFFECTS PRODUCED ON TKEES AND SHEUBS 



"ird, Atmospheric pollution by smoke, aud other noxious 

 vapours or gaseous discharges, -s^'hereby the pure natural air is 

 vitiated, aud rendered injurious to the respiratory organs of 

 vegetable life, and an artiticial atmosphere, as it were, by long 

 continuance of constant smoke exhalations, is created, inimical to 

 growth of plants, from its containing in excess large amounts of 

 sulphurous and acid vapours. 



Sometimes the effects so produced are individually sufficient 

 to constitute a serious sanitary objection to tlie continuance of 

 the works which cause them; but in many instances, where the 

 intelligent practical application of chemical science and engineer- 

 ing has been called in to aid in mitigating or entirely removing 

 the evils complained of, success has been achieved, wdthout 

 injuriously interfering with the industrial pursuits of those 

 engaged in the particular manufacture ; and it is to be hoped 

 that in many other cases, where no remedial measures have as 

 yet been attempted, — manufacturers will yet see it to be their 

 duty, — while carrying on advantageously to themselves their 

 commercial euterprizes, — to use every effort which science and 

 experience may discover or suggest, to mitigate evils inseparably 

 connected with their processes, but which are capable of ame- 

 lioration in the interests of the amenities of nature and their 

 neighbourhood generally. 



With the clamant evils of river pollution, the government, 

 last session, endeavoured (unfortunately without success) to 

 grapple, but the subject is so important, that once fairly roused, 

 as it has been, it will probably again form matter for legislation, 

 until successfully settled; and in that way an immense source 

 of destruction to vegetable life %vill be put an end to. With the 

 gaseous vapours and smoke discharges from large public works 

 polluting the air for miles around, the question is a more difficult 

 one, and a problem of greater intricacy, and it is with the effects 

 produced by this species of destruction to trees and shrubs that 

 w^e have in this paper more particularly to deal at present. 



Without specifying in detail the various noxious chemical 

 ingredients discharged from large public works, and which differ 

 in the degree and extent of injury which they create, according 

 to the nature of their chemical composition, and vary accord- 

 ing to the special description of work or process whence they 

 emanate, it may be generally stated that the primary and chief 

 destruction to vegetation in the neighbourhood of such works, 

 or large towns, is caused by the sraohc discharges from them, 

 arising from the combustion of coal in furnaces, and by the gases 

 and vapours that are produced during metallurgical processes af 

 the chemical arts and manufactures. Vegetable life, in general, 

 is very susceptible of impurities existing in the air around it, 

 and even slight modifications in the proportions of its constituent 



