66 HUMAN PHYSIOLOGY CHAP. 



it tightly with the hand and shake thoroughly. If the limewater 

 turns milky the ventilation needs immediate attention. If the lime- 

 water is not changed at all, the amount of carbon dioxid in the air 

 is comparatively small. 



60. Method of Ventilation. If the room is heated 

 with a hot-air furnace, the entrance of fresh air will take 



Wcare of itself. The pure air from out- 

 side enters the furnace jacket, where it 

 is warmed, and then it passes up into 

 the room. Care must be taken to keep 

 the foul-air flues open, so as to per : 

 /\_ mit the bad air to escape. This is one 



of the most satisfactory means of heat- 

 ing and ventilating at the same time. 



If the room is Jieated with a stove, 

 you must provide for a similar circula- 

 tion through the room. Fresh air must 

 come in from outside, pass through the 

 room, and escape as fast as it becomes 

 >&W0 unfit for breathing. How can this be 

 done ? Open windows are dangerous, 



FIG. 31. Window . . ., . .. . 



ventilation f r jt 1S impossible to avoid drafts in 



(Zuppke). some part of the room in very cold 



weather. A simple method, if the room is large, is to 

 fit a board tightly under the lower sash of every win- 

 dow. It should be as wide as the window and just high 

 enough to permit good circulation between the two 

 sashes, as shown in the figure above. 



Another method is to lower the upper sash and pro- 

 vide some means for throwing the fresh air upward as 



