THE CHEMISTRY OF CLEANING. loi 



THE CHEMISTRY OF CLEANING.* 



By Pkof. VIVIAN LEWES. 



AS a great city grows, and the agglomeration of struggling 

 liumanity increases, such questions as the disposal of sew- 

 age and other waste matter rise from comparative insignificance 

 into problems of almost insurmountable difficulty ; and while 

 we are able to put the burden of cleansing our towns upon the 

 urban authorities, the responsibility of keeping our homes and 

 bodies in a condition of at least sanitary cleanliness devolves 

 upon the individual, and a knowledge of the causes of dirt and 

 the methods by which it can be removed can not be regarded 

 as devoid of interest, or at any rate of utility. 



Observation shows that in our town houses only a very short 

 interval of time is needed to cause a considerable deposit of dust 

 upon any horizontal surface, while vertical surfaces and draper- 

 ies, especially if their surface be rough, also accumulate a per- 

 ceptible quantity, although of a lighter and more finely divided 

 kind. We also find that this dust is borne to its resting place by 

 the air which penetrates from the outer atmosphere, and that its 

 deposition is caused by the comparative condition of rest insured 

 to it by the absence of wind or violent currents. 



The presence of these air-borne particles of solid matter can be 

 made visible in any town by allowing a beam of sunlight or a ray 

 from an electric lantern to pass through the air of a darkened 

 toom. If the room be filled with air previously filtered by pass- 

 ing it through cotton wool, the beam of light is invisible until it 

 strikes the opposite wall; but if the air be unfiltered, the path of 

 the beam is mapped out by the suspended matter reflecting and 

 dispersing portions of it, and so becoming visible to the eye as 

 " the motes in the sunbeam." The heavier the nature of the par- 

 ticles the more quickly will they settle, with the result that the 

 dust on horizontal surfaces, such as the tops of sideboard, piano, 

 and mantel-board, may be expected to differ somewhat from the 

 lighter form, which has continued to float until contact with ver- 

 tical surfaces has brought it to rest. 



These particles of dust are composed of matters of the most 

 varied nature, and will be found, when collected, to consist partly 

 of mineral and partly of organic substances. 



The heavier portions of the dust are found to contain ground- 

 up siliceous matter, pulverized by traffic in the road ; small parti- 

 cles of salt carried inland by winds from the sea, together with 

 sulphate of soda, with other impurities of a local character. If a 



* Abridged from a lecture delivered at the London Institution. 



