[163] The ashes are mixed with chaff, chopped straw, refuse hay, grass cuttings, dry street sweepings, wool and hair, shoddy, &c., and a small percentage of sulphate of iron or lime. [164] Professor Tyndall, in his beautiful experiments, has proved that dusty air is alive with the germs of the bacteria of putrefaction, whilst the pure fresh air which he gathered on a mountain peak in the Alps is innocent of such germs, and is absolutely powerless to produce any organisms. [165] Dry dust will absorb about ten times its bulk of water, thus swelling considerably and producing the greasy mud so often seen after rain. [166] In Boston, U.S.A., the macadamised roads are not swept at all, as it is considered that by sweeping off the sand and detritus their durability is much lessened, but their gutters are cleansed as required, and rubbish picked up. (_Vide_ ‘Minutes of Proceedings Institution of Civil Engineers,’ vol. lxiii. p. 368.) [167] In Regent Street, London, in November 1881, I saw four loads of mud removed from about 1000 square yards of surface, it being then almost new wood pavement. [168] See note under “Other Obstructions and Nuisances,” p. 155, 8th edition, Glen’s ‘Law of Public Health and Local Government.’ [169] _Vide_ ‘Report to the Streets Committee of the Honourable the Commissioners of Sewers of the City of London on Melting Snow by Clarke’s Apparatus,’ by William Haywood, Engineer and Surveyor to the Commission, 1881, p. 9. [170] With regard to the removal of snow from the footpaths, it is highly desirable that this should be effected by the occupiers of the premises adjacent to the street, as otherwise it adds immensely to the work of the local authority. The following interesting remarks by the superintendent of the scavenging department of Liverpool will be no doubt read with great interest: “The only way to compass the removal of snow from the footwalks of the principal thoroughfares within a comparatively short time, is by sprinkling them with salt, such as is commonly used for agricultural purposes. It is certain that, unaided by the salt, a sufficient number of men cannot be procured for the emergency of clearing snow from the footways of the most important thoroughfares. It has been stated by medical authorities that the application of salt to snow is detrimental to the health of people who have to walk through the ‘slush’ produced by the mixture, and that the excessive cooling of the air surrounding the places where the application has been made is injurious to delicate persons. It therefore seems that the application of salt to snow should not be undertaken during the day time, but should be commenced not before 11 p.m., nor continued after 6 a.m., and that only such an area of footwalks should be so treated on any one night as the available staff of men can clear by an early hour the following morning.