488 



SCIENCE 



[N. S. Vol. XXXIII. No. 



ments, under the auspices of the Carnegie In- 

 stitution or the Eussell Sage Foundation, to 

 discover by direct experiment on a large scale, 

 the effect upon the health and comfort of 

 school children, of the three different systems 

 of ventilation: (A) Open windows, as recom- 

 mended by Doctors Thompson and Brennan, 



(B) the plenum system recommended by Dr. 

 Hill, with low temperature and high humidity, 



(C) the American plenum system with 70° 

 temperature and low humidity. 



For the carrying out of a portion of the re- 

 search, I suggest that experiments be made in 

 several rooms of a large grammar school, all 

 with the same window exposure and light, one 

 room being treated by direct radiation and all 

 ventilation obtained by open windows, and 

 others by the plenum system, with the volume, 

 temperature and humidity regulated at will. 

 Let the rooms be thoroughly aired, say from 



8 to 8.30 A.M., then when the children enter at 



9 A.M. have their condition noted by trained 

 specialists, with all the known pathologic and 

 psychopathic tests, including the use of instru- 

 ments for recording the pulse and the respira- 

 tion, " reaction time," etc., and let these tests 

 be repeated at noon. Tests should also be 

 made to determine relative mental fatigue, 

 lack of attention, etc. Statistics should be 

 collected to determine what relation, if any, 

 exists between the ventilating system or qual- 

 ity and quantity of ventilation in the schools 

 and the prevalence of adenoids, sore-throat, 

 headache, colds, etc. It may be found that 

 these troubles have relation to the environ- 

 ment of the child during the nineteen hours 

 that he is out of school rather than the five 

 hours that he is in school. 



Experiments should be made to find whether 

 the percentage of CO^ in the school room has 

 the relation to the child's health or mental 

 vigor that it has been commonly supposed to 

 have, and whether an air supply of 600 or 

 1,200 cubic feet per hour per pupil, instead of 

 1,800, produces any bad efl^ects. Bacterial ex- 

 amination of the air should be made at the 

 same time. 



Such a research as is suggested will take a 

 long time and will cost much money, but is 

 there any investigation now under way that is 



more worth the money, or that promises more 

 for the welfare of the race? 



William Kent 



To THE Editor of Science : I am writing in 

 the endeavor to clear up some of the elemen- 

 tary questions asked by Dr. Luther H. Gulick 

 in his letter " The Air "We Breathe," published 

 in Science of March 3. 



When air is completely saturated with water 

 vapor, the humidity in it is vapor, that is, a 

 gas at point of condensation. At other times 

 humidity is a gas, just as. much so as C0„, it 

 is in fact superheated steam in the air. A gas 

 just ready to condense to liquid is called vapor ; 

 thus, ordinary steam is a vapor, while super- 

 heated steam is a gas, obeying all the well- 

 known gas laws. Humidity is a vapor when- 

 ever the air is completely saturated, being then 

 the same as ordinary steam in the air; when, 

 as is usually the case, air is unsaturated, then 

 humidity is superheated steam in the air — a 

 gas. Heat added to vapor superheats it, that 

 is, raises its temperature. Heat taken from 

 vapor condenses some of the vapor to liquid 

 without altering the temperature. 



Liquids remain in the liquid state only by 

 virtue of external pressure exerted upon them, 

 and any liquid will quickly turn to gas if all 

 external pressure (which is usually that 

 exerted by the atmosphere) is removed; the 

 tendency for a liquid to gasify depends upon 

 the temperature and kind of liquid, and noth- 

 ing else. 



If a closed vessel containing water and air 

 is let stand at any temperature until condi- 

 tions have become constant the air will grad- 

 ually become saturated with water vapor, and 

 the amount of water vapor that will be thus 

 absorbed by a given volume of air will de- 

 pend only on the temperature of the air; it 

 would, moreover, practically be not only inde- 

 pendent of the pressure of the air, but would 

 be the same if another gas or even a vacuum 

 were substituted for the air; also the pressure 

 exerted by the water vapor filling the given 

 space at a given temperature would be the 

 same in all these instances. 



In a gas mixture the total pressure exerted 

 by the mixture upon the walls of a containing 



