The Air of Sewers. 



501 



As it was frozen to the collar C, and therefore unable to expand 

 upwards, since both collars were fixed to a frame, the cylindrical part 

 of the ice bulged outwards, as in the usual case of a long column 

 under compression. When the specimen was subsequently exposed 

 to tension, the effect of the latter was to straighten it, so that in a 

 few days it no longer bulged out. The straightening of the central 

 line of the ice cylinder thus gave rise to greater extensions than were 

 due simply to the extension of a straight bar of ice with an equal dis- 

 tance in all azimuths between the rings. 



"The Air of Sewers." By Professor Thomas Carnelley, 

 D.Sc., and J. S. Haldane, M.A., M.B., University College, 

 Dundee. Communicated by Sir H. ROSCOE, F.R.S. Re- 

 ceived May 21.— Read June 16, 1887. 



Owing to the complaints which had been made of bad smells in the 

 House of Commons, a Select Committee was appointed in the sprin g 

 of 1886 to inquire into the ventilation of the House. In consequence 

 of the experience we had gained in the course of an extensive exami- 

 nation of the air of houses and schools in Dundee (see ' Phil. Trans.,' 

 vol. 178 (1887), B, p. 61), we were instructed by the Committee to 

 make a series of analyses of the air in the sewers under the Houses 

 of Parliament, and to report thereon (see ' Second Report of the 

 Committee,' Appendix). Since then we have examined the air in 

 a considerable number of sewers in Dundee. 



Our object was, in the first place, to obtain a general idea of the 

 amount of some of the more important impurities present in sewer 

 air. But we have also endeavoured to throw some light on their 

 sources, and on the conditions affecting their dissemination. With 

 this view we found it desirable to supplement our observations in the 

 sewers by a certain number of laboratory experiments. 



In spite of the great amount of discussion which has taken place 

 in connexion with real and supposed danger from sewer air, there 

 have hitherto been but few analyses published of the air of sewers of 

 modern construction. 



The first and most complete set of analyses was that made by 

 Dr. Letheby in 1857-58 ('Report to the City of London Commissioners 

 of Sewers,' 1858). He examined the air of thirteen sewers in the 

 City of London. The following are the means of his analyses : — 



vol. XLII. 



