The actual component parts, however, of any gases in a sewer must vary considerably with its conditions and locality, &c., in the same manner as they would in any public building or room, and it is impossible to tell, without costly experiments, what gases may be prevalent in any particular portion of a sewer. But whatever may be the analysis of this foul air, there can be but little doubt that it contains organic matter floating about in it as solids, and that it is excessively injurious and even dangerous to breathe, and that it should be caught and destroyed or rendered innocuous, and not be permitted to pass into and contaminate and poison the air we breathe.
Some engineers are of opinion that this foul air always finds its way to the upper portions of the sewerage system, but my investigations into this subject have led me to believe that no rule of this kind can be laid down, for with quick velocities of flow, in some sewers, the gases are carried by friction in the direction of the flow of the sewage, and do not ascend as has been imagined.
Whatever system of ventilation of the main sewers in any town may be adopted, it is imperative that the house drains connected with them should be properly trapped and ventilated, and this is in my judgment of even greater importance than the ventilation of the main sewers. On this point I have given more explanations in the chapter upon “[House Drainage].”
In conclusion, let me refer my readers to a most exhaustive discussion, and very valuable information contained in the chapter entitled “Ventilation of Sewers and Drains” in Mr. Baldwin Latham’s ‘Sanitary Engineering,’ in which may be found almost everything that is at present known upon this important subject.
[193] If there is any truth in the “germ theory” of disease, how dangerous must be the practice of open sewer ventilation, a waft of foul air from a sewer carrying with it a germ, and the unsuspecting passer-by is inoculated just as surely as if he had handled or been near the excrements of the diseased person whose evacuations have been passed into the public sewer.
[194] The important city of Bristol has no system of sewer ventilation, and yet the death rate of the city, which is by no means specially healthily situated, has not been abnormally high up to this year (1883).
[195] For further information upon my system for the annihilation of sewer gases, I must refer my readers to a pamphlet written by myself in 1880, entitled ‘Sewer Ventilation, or a New and Improved System for the disposal of the Noxious Gases generated in Sewers and Drains,’ and also to a paper I read on this subject at the meeting of the Sanitary Institute of Great Britain, held in Exeter in the year 1881.