VENTILATION AND CONSTRUCTION OF STABLES. 3 



words, of maintaining in their due proportion the proper constituents of 

 the air. But in a closed room or stable there are no means by which she 

 can carry on her restorative processes. Hence the need of ventilation. 

 It is absolutely necessary to maintain or restore the proper constituents 

 of the air, if we wish for health for ourselves or our horses. 



6. Natural facilities for ventilation. 



Fortunately the peculiar properties, or rather the state of the gases 

 which respectively constitute foul and pure air, afford great facilities for 

 ventilation. Heat causes all matters to expand, some more and some 

 less ; but gases under the influence of heat expand very rapidly, and to 

 a very great degree ; and as they expand, they of course become lighter. 



As a general rule, foul air in a stable is also heated air. It is only 

 necessary to breathe on the hand to feel that our breath is generally 

 warmer than the air. And besides the breath a certain amount of heat 

 is given off from the bodies of all living animals. Carbonic acid gas, 

 though at equal temperatures heavier, is nevertheless, when heated, as it 

 is when first given off from the lungs, lighter than pure air. 



7. Escape of foul air. 



The lightness of heated foul air at once affords the key for getting rid 

 of it. It is only necessary to provide the means of exit in the highest 

 part of the stable, and it will escape by its own inherent lightness. In 

 fact we may get quit of it without any trouble. 



But, on the other hand, supposing that the foul air has no means of 

 escape, what becomes of it? It has risen to the top of the stable, 

 because being heated it is lighter than the surrounding air. It will 

 escape if it can, but if we deny it the opportvmity of doing so, it must 

 remain in the stable. It then gradually cools, and as it cools descends 

 and becomes mingled with the air of the stable, and is in due course 

 again presented to the nostrils to be breathed. 



Although we cannot see this movement of foul air in a room or stable, 

 it may easily be shown by experiments with coloured gases. 



8. Hoio the place of the foul air is supplied. 



But supposing the foul air to have an exit above, how is its place, how 

 is the vacancy caused by its escape, to be supplied by fresh air? 



If there are no apertures except those above, it is clear that by the 

 continued ascent and escape of heated foul air a tendency to a vacuum 

 will be created in the stable. It is well known that the pressure of the 

 atmosphere is equal to 14 lbs. per square inch. When, then, even a 

 tendency to a vacuum has been created, the pressure of the air on the 

 outside is siifficient to overcome the upward current of heated air ; and 

 cold, fresh air will rush in at intervals to supply the vacancy. When the 

 vacancy is supplied, the upward current and escape of heated air will be 

 resumed until another tendencv to a vacuum is created, when a similar 



