100 CHEMISTRY. 



see by the arrangement of the tubes that the air which is 

 breathed in must come through the vessel at the left hand, 

 while that which is breathed out must pass out through the 

 other. In this latter, of course, will be seen the milky ap- 

 pearance. The reaction in these experiments is thus ex- 

 pressed : 

 Lime-water, Carbonic anhydride, Calcium carbonate, Water, 



CaH 3 O 3 + CO a CaC0 3 + H 2 O. 



126. Ventilation. The importance of free ventilation in 

 our apartments, and especially in lecture - rooms, public 

 halls, churches, etc., results from this production of carbon- 

 ic anhydride in our respiration. Wherever breathing is 

 going on there will be an accumulation of this gas, unless 

 there be suitable facilities for its diffusion in the atmos- 

 phere. Where there are only a few persons in a room, the 

 escape of this gas and the introduction of fresh air are ef- 

 fected sufficiently by means of the crevices here and there, 

 together with the occasional opening of the doors, and a 

 thorough ventilation once a day by opening the windows. 

 But when many are gathered together, other means are re- 

 quired. It costs something to have good air in thronged 

 places of concourse, not merely from the apparatus required, 

 but from the additional fuel necessary to maintain warmth 

 with the afflux of cold air from without. But it must be re- 

 membered that good air is a valuable commodity. The bad 

 influence of imperfect ventilation upon the health is not ap- 

 preciated because it is so gradual. Multitudes are constant- 

 ly undermining their health by sleeping in small chambers 

 with no proper means of ventilation, and occasionally tak- 

 ing an extra dose of the poison into their lungs in crowded 

 assemblies. While the community are struck with horror 

 at the sudden destruction of a few lives in such a case as 

 that of the Black Hole of Calcutta, the slow and constant 

 destruction of multitudes by the gradual introduction of 



