THE SANITATION OF AIR 27 



beyond, or even as far as, making up the deficiency caused by heating, 

 since the human system is used to considerable changes without any 

 real discomfort. Indeed, dry air, if pure, is probably more beneficial 

 to normal adults than moist air. The principal reason why the demand 

 for moisture in heated rooms has arisen is the irritating effect of float- 

 ing dust which has been set in motion by the heating system, directly 

 or indirectly. In the worst form this may be noticed with hot-air 

 heating through floor registers, which invite all sorts of rubbish to fall 

 into the flue, only to be dried and sent up again, often directly into 

 one's nose. Radiators also, especially those with inaccessible surfaces, 

 will gather dust. When cold, it will lay there and molest no more 

 than that on furniture, but as soon as heat is turned on, the tiny drops 

 of moisture, which always cling to these solid particles, will evaporate. 

 Free of this weight, the dust is easily set in motion by the currents of 

 warm air rising from the radiator, as may often be seen by the tell-tale 

 shadows on the wall above. Heating apparatus thus contaminates the 

 air with dust and bacteria which otherwise would lay undisturbed and 

 out of harm's way. Moistening of the air will not prevent this to any 

 extent. It increases, in fact, another source of contamination, still too 

 common with modern heating systems — the dry distillation of the 

 organic matter on hot surfaces. This phenomenon has recently been 

 studied by the noted hygienists Professors Esmarch and Nussbaum, 

 who have independently reached the conclusion, that organic dust begins 

 to distil or singe when a radiator reaches a temperature of about 

 165° F., and that this process is rather encouraged by moisture, prob- 

 ably because the hygroscopic matter clings longer to the heated surfaces 

 and is therefore decomposed before it rises up in the air. To reduce' 

 the vitiating effect of heating apparatus, we must insist on the most 

 accessible and simple styles of radiators, on which any dust can readily 

 be seen and is apt to be removed, and on ample heating surfaces of 

 moderate temperature which will tend to avoid the decomposition of 

 organic matter. 



Overheating by itself must be considered as vitiating the air; at 

 least in so far as it makes it unfit, or less wholesome, according to some 

 noted hygienists who have thoroughly investigated its effect. It seems, 

 at any rate, to give the air a lifeless quality, which soon imparts itself 

 to the victim of our wasteful modes of heating. 



Apparatus for artificial moistening, which is now often installed 

 in connection with heating and ventilating systems, aside from the 

 liability of exceeding the desirable humidity, also gives opportunity for 

 contamination of the air supply. Unless the devices are designed on 

 sanitary principles and intelligently attended to, they are very liable to 

 become foul and malodorous, if not unhealthy. 



Like the heating of buildings, artificial cooling may also have un- 



