HiGGiNSON. — Sanitary Sewerage. 373 



Clark, though the latter adnntted a large proportion of rain- 

 fall. In explanation of the term, I may state that only the 

 house-sewage is admitted, the surface-water and ordinary 

 drainage being carried bv distinct drains into the natural 

 watercoui'ses, and so to the nearest river or sea, as the case 

 may be. By the adoption of the separate system we are 

 enabled to calculate almost exactly what quantity we have to 

 deal with, as the discharge wull closely correspond with the 

 amount of w^ater supplied to the population for domestic 

 purposes, and we are not called upon to provide for an un- 

 known quantity, which must be the case w^hen the rainfall is 

 admitted. 



The separate and hydro-pneumatic systems are in no 

 sense interdependent parts of one scheme, the only connec- 

 tion between them being that the cost of the introduction of 

 the "separate" system is very much reduced when com- 

 pressed air is made use of in ejectors. 



The application of compressed air as a transmitting medium 

 has been of late extensively adopted in a variety of ways. 

 There is nothing visionary or unpractical in urging its adop- 

 tion, for it has been indorsed with the approval of most prac- 

 tical men of our time. Where the burning of town-refuse in 

 a " destructor " furnace is carried out we have the power for 

 compressing the air free of expense. It is a motive-power 

 which, once produced, can be conveyed and divided amongst 

 any number of stations at va;rying distances with little loss. 

 It is open to question whether the use of air or water can be 

 most economically adopted for the transmission of power. 

 This has been much debated of late. Suffice it to say that 

 for the purpose of transmitting sewage by Shone's system 

 air is alone applicable. The loss from friction in the pipes is 

 much less for air than water, and its compression is now well 

 understood, rapid strides having of late been made in the per- 

 fection of the necessary machinery for the purpose. 



In properly designing sewers one of the chief objects to be 

 attained is that they shall be self-cleaning — that is, they shall 

 be laid at such inclination as will generate a velocity which 

 will prevent deposit. Where this is not the case they rapidly 

 fail to act, necessitating constant expenditure to free them 

 from obstructions, which is the source of the foul gas so de- 

 leterious to the occupants of houses with which they are con- 

 nected. 



Baldwin Latham states that "undoubtedly an open drain 

 is the least injurious form of sewer, provided stagnation is 

 avoided, and that in proportion as the sewers are enclosed the 

 danger to health is increased. The usual remedies are to trap, 

 ventilate, and flush the drains — measures which only succeed 

 in partially remedying a defect that should not exist." 



