572 KANSAS CITY REVIEW OF SCIENCE. 



of fixtures. A multitude of fixtures requires a large number of soil and waste 

 pipe-stacks, and the chance of leakage of sewer gas through defective joints in- 

 creases correspondingly. But be the house large or small, its drainage and 

 plumbing system should always be so arranged as entirely to exclude any possi- 

 bility of the escape of sewer gas. 



Sewer Gas. — I shall, first, briefly consider what is meant by the terrn 

 "sewer gas. This term, as Prof. W. Ripley Nichols has truly said, ^ is "an 

 unfortunate one, and gives rise to a quite widespread but very erroneous idea. 

 Many seem to suppose the ' sewer gas ' to be a distinct gaseous substance, which 

 is possessed of marked distinguishing characteristics, which fills the ordinary sewers 

 and connecting drains, and which, as a tangible something, finds its way through 

 any opening made by chance or by intention, and then, and only then, mixes 

 with the atmospheric air." 



Sewer gas is a mechanical mixture of a number of well known gases, having 

 their origin in the decomposition of animal or vegetable matter, with atmospheric 

 air. This mixture is continually varying, according to the more or less advanced 

 stage of putrefaction of the foul matters, which form a sediment and a slimy coat- 

 ing of the inner surfaces in drains and pipes. It is -also variable with the charac- 

 ter of this sediment or deposit, and with the physical conditions (moisture, heat, 

 etc.) under which the decomposition tikes place. 



The principal gases found in sewers and drains are oxygen, nitrogen, car- 

 bonic dioxide, carbonic oxide, ammonia, carbonate of ammonia, sulphide of am- 

 monium, sulphuretted hydrogen and marsh gas. 



The three first-named gases are the principal constituents of the atmosphere 

 surrounding the globe, and are found present in the following average propor- 

 tion, viz : 



20.9 vols, oxygen ] in 100 vols, of air, together with 2 to 5 vols, carbonic diox- 

 79.1 vols, nitrogen) ide in 10,000 vols, of air. 



According to R. Angus Smith the amount oi oxygen'x's,: 



In the average, 20.96 vols, in 100 vols, of air. 



In pure mountain air, 20.98 vols, in 100 vols, of air. 



At the sea shore, 20.999 vols, in 100 vols, of air. 



In streets of populous cities, 20.87 to 20.90 vols, in 100 vols, of air. 



The air in sewers and drains contains much less oxygen, as some of it com- 

 bines with the carbon of putrefying organic matter forming carbonic dioxide. 

 The amount of nitrogen in the air of sewers is little different from that in the at- 

 mosphere which we breathe; but the amount of carbonic dioxide present is greatly 

 increased. 



The lowest amount of oxygen in sewer air is recorded to be 17.4 vols, in 100 

 vols, of air; the amount of carbonic dioxide is in the average 2.3 vols, in 100 vols. 

 Sulphuretted hydrogen varies greatly, but the quantity is generally so small as not 



1 See Frcf. RipUy Nichols' Report upcn Chemical Ex:mination of the Air of the Berkeley S reet 

 S-vver, in Bo.tor, Mass., 1S78. 



