1877.] Solid and Liquid Particles in Seiver Gases. 545 



open ends over the top o£ the paper tube. The tin tube was nearly ho- 

 rizontal but slightly inclined upwards from the paper tube, so as to cause 

 a gentle draught of air to pass through it when it was slightly heated 

 externally near its lower extremity. A Bunsen flame placed at the end 

 of this tube furthest away from the effervescing liquid showed that the 

 suspended particles of solution of lithic chloride were not perceptibly less 

 numerous than at the mouth of the paper tube ; neither were they much 

 diminished at the further end of the tin tube when the height of the paper 

 tube was increased to 9| feet. There can, I think, be little doubt that 

 these particles, which had thus been carried aloug by a gentle current of 

 air for a distance of 21 feet, would be similarly conveyed to very much 

 greater distances. 



Li some of my earlier experiments I had noticed that the suspended 

 particles in a current of air were diminished in number, or sometimes alto- 

 gether removed, when the current had to pass a right-angled bend in a 

 tube ; and it therefore appeared to be not unlikely that a stratum of small 

 fragments of charcoal M'ould arrest them. This surmise, however, did 

 not prove to be correct ; for the particles of lithic chloride solution sus- 

 pended in air, when the latter was moving very slowly, passed easily 

 through a stratum 2 inches thick, composed of fragments of charcoal 

 varying in size from | to 1 cubic inch ; and even when the thickness of 

 the stratum was increased to 5 inches, the particles still came through 

 although in greatly diminished numbers. 



The following conclusions as to the behaviour of flowing sewage may 

 be drawn from these experiments : — 



1. The moderate agitation of a liquid does not cause the suspension of 

 liquid particles capable of transport by the circumambient air ; and there- 

 fore the flow of fresh sewage through a properly constructed sewer is 

 not likely to be attended by the suspension of zymotic matters in the air 

 of the sewer. 



2. The breaking of minute gas-bubbles on the surface of a liquid con- 

 sequent upon the generation of gas within the body of the liquid is a 

 potent cause of the suspension of transportable liquid particles in the sur- 

 rounding air ; and therefore when, through the stagnation of sewage or 

 constructive defects which allow of the retention of excrementitious 

 matters for several days in the sewer, putrefaction sets in and causes the 

 generation of gases, the suspension of zymotic matters in the air of the 

 sewer is extremely likely to occur. 



3. It is therefore of the greatest importance to the health of towns, 

 villages, and even isolated houses, that foul liquids should pass freely and 

 quickly through sewers and drain-pipes, so as to secure their discharge 

 from the sewerage system before putrefaction sets in. 



