1877.] 



Solid and Liquid Particles in Sewer Gases. 



543 



rare as that of London still offers sufficient resistance to the subsidence 

 of minute suspended particles to prevent them from falling more rapidly 

 than one inch per minute, the globular flasks in which the experiments 

 were made being only about 8 inches in diameter. Such particles could 

 not therefore be left behind by an ascending current of the slightly rare- 

 fied air produced by an increase of temperature to 100° C* 



In addition to these aqueous and other volatile particles which dis- 

 appear by a gentle heat, there are also others which consist partly of 

 organic and partly of mineral matters. But the organic seem greatly to 

 preponderate in the air of towns, because such air becomes ajy^arently 

 perfectly clear after it has been ignited. 



The processes of fermentation, putrefaction, and decay afford abundant 

 evidence that zymotic and other liviiig germs are present amongst the 

 organic portion of the suspended matters ; whilst many analyses of rain- 

 water, made by myself and others, show that the salts of sea-water are 

 amongst the mineral constituents floating in the atmosphere. 



Of the zymotic matters, those which produce disease in man are ob- 

 viously of the greatest importance; and it was chiefly ^dth the object of 

 ascertaining the conditions under which these poisons become suspended 

 in the air that I undertook the experiments, the results of which I have 

 now the honour to communicate to the Eoyal Society. 



The outbreak of Asiatic cholera in Southampton in the year 1866 was 

 traced by the late Professor Parkes, P.E.S., to the dispersion of infected 

 sewage through the air. The sewage became infected by the intestinal 

 discharges from some cholera patients who landed from the Peninsular 

 and Oriental Company's steamship ' Poonah.' 



In this case the dispersion was produced by the pumping of the infected 

 sewage and its discharge, in a frothy condition, down an open channel 

 8 or 9 feet long. The effluvium disengaged from this seething stream 

 was described as overpowering, and was bitterly complained of by the 

 inhabitants of the adjacent clean and airy houses, amongst whom a viru- 

 lent epidemic of Asiatic cholera broke out a few days after the sewage 

 received the infected dejections. Nevertheless the discharge of the frothy 

 liquid was kept up day and night for about a fortuight, and 107 persons 

 perished. At length a closed iron pipe was substituted for the open con- 

 duit : from that day the number of cholera cases diminished, and within 

 a week of the protection of the conduit the epidemic was virtually over. 



* When this paper was read, Professor Stokes called my attention to the fact that 

 the time of subsidence of solid particles in a gas depends upon the viscosity, and not 

 upon the specific gravity, of the gas. The viscosity of gases is directly as their times of 

 transpiration, and is increased when they are expanded by heat. The time of transpira- 

 tion of hydrogen is nearly half that of air, and hence suspended matters ought to sub- 

 side twice as quickly in hydrogen as in air. The slight excess of viscosity of the 

 hj'drogen used in these experiments was doubtless due to the almost unavoidable 

 admixture of traces of air, for Graham found the transpiration time of hydrogen to be 

 greatly prolonged by admixture with oxygen. — Feb. 17, 1877. 



