102 THE POPULAR SCIENCE MONTHLY. 



sample of dust be collected and carefully ignited, the organic 

 matter will be burned away and any ammonium salts volatilized, 

 while the mineral portion will be unacted upon ; and in this way 

 it has been shown that more than one half of the suspended mat- 

 ters in the air are of organic origin, a large portion of this organic 

 matter consisting of germs which are capable of setting up fer- 

 mentation, disease, and decay. 



It is only within the last few years that the importance of the 

 work done by the solid particles of dust floating in the air has 

 been recognized, and it is to Pasteur that we owe the knowledge 

 that these germs set up the various processes of organic decay, 

 by which the waste matter derived from vegetable sources is once 

 again resolved into the water vapor and carbon dioxide used by 

 Nature as the foundation of all organic creations. It is the almost 

 imperceptible germs floating in the air which start this marvelous 

 natural action germs so minute that it requires the strongest 

 microscope to detect them, yet so potent that the whole balance 

 of life hangs on their existence. These facts show us that not 

 only has dust a most marvelous history, but that in it Nature has 

 disguised her most important factor for cleaning the face of the 

 earth from waste matter of both mineral and vegetable origin. 



The surface soil when mixed with water gives the mud which 

 dirties our boots, and forms clots on the train of our skirts ; but 

 this, as well as the dust which has settled in our living rooms, 

 and merely clings mechanically to the surfaces upon which it has 

 deposited, may be removed by such simple physical means as the 

 duster and brush. When dust has found its way into a fabric 

 such as a carpet, it requires considerable force to again dislodge 

 it, and this is applied by means of the broom ; but in vigorous 

 sweeping we find that the largest proportion of the dust is driven 

 up into the air, only to resettle once again on other surfaces, so 

 that although we can make the nuisance " move on," we do not 

 in this way remove it, and experience has taught our servants 

 that wet tea-leaves scattered on the carpet before sweej^ing lessen 

 this evil. In some cases, instead of using this method, it has been 

 argued that it must be the moisture which acts in preventing the 

 raising of the dust, and the carpet has been sprinkled with water. 

 This converts the dust into mud, which remains fixed in the 

 fabric while the sweeping is going on, but as soon as the water 

 has evaporated from it, again reasserts its right of rising as dust. 



When, however, wet tea-leaves, damp sawdust, or even moist- 

 ened sand is scattered over the surface to be swept, the dust when 

 dislodged adheres to the moistened substance and is removed. In 

 choosing moist bodies for this purpose, the only points to con- 

 sider are that they must have no staining action on the carpet, 

 must not be too wet, and must not be so finely grained as to 



