VENTILATION 57 



it here as bearing out the necessity for a large supply of 

 pure air. 



CUBIC SPACE. 



Great stress has been laid on the importance of a large 

 cubic space, as in the minds of some people there is an idea 

 that by having a larger air space there is less necessity for 

 ventilation. A large cubic space is a most desirable condi- 

 tion but not for the reason just mentioned. 



The larger the air space the smaller the number of times 

 per hour the air of that space has to be changed, and hence 

 the less chance of draught. An example will explain the 

 position. If two stables be taken, one of 600 feet the other 

 of 1,500 feet contents, each of these must supply exactly the 

 same amount of fresh air per hour to the occupant, viz. 

 15,000 cubic feet. But the air in the 600 feet stable will 

 require to be changed a little more than twenty-five times 

 an hour, whereas in the stable of 1,500 feet the air need 

 only be changed ten times per hour. 



Cubic space does not render ventilation less necessary, 

 the stable of 1,500 feet without ventilation will become just 

 as foul as the one of 600 feet, only it will take about double 

 the time in the large stable to render the air as impure 

 as in the small one. Once the air impurities are the 

 same they both, irrespective of the difference in their 

 capacity, must supply exactly the same amount of air ; in 

 other words, the value of cubic space soon vanishes unless 

 regular ventilation is established. 



The table on the next page, calculated from de Chaumont's 

 equation, will enable this point to be understood. 



The objection against small cubic space, as stated above, 

 is that the air requires changing a large number of times in 

 the hour to supply the amount necessary. It therefore has 

 the drawback that such a stable would be draughty if 

 properly ventilated ; also, if the conditions which bring 

 about natural ventilation become suspended or interfered 

 with, the air contents of a small stable become more rapidly 

 impure than those of a large one. 



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