VENTILATION 87 



Let us suppose on entering the stable the air smells close ; 

 from the table the amount of respiratory vitiation present 

 would be about -6708 per 1,000 volumes of air, therefore 



^8 = '-''- 



As the observed ratio is expressed per 1,000 volumes 

 the answer must represent the number of thousands of 

 volumes ; in the above example, each horse was supplied 

 with 4,460 cubic feet of fresh air per hour, instead of 15,000 

 cubic feet. 



Estimation of Carbonic Acid. — If possible the examination 

 by the senses should be supplemented by the determination 

 of carbonic acid in the building. The process is a very 

 simple one and depends upon the power lime or baryta 

 water has of absorbing carbonic acid. The alkalinity of 

 either of these is first ascertained by a solution of acid of 

 known strength ; after absorbing carbonic acid the baryta 

 or lime water loses a certain amount of its alkalinity, and 

 the amount of this loss is determined by again treating 

 with the standard acid solution ; the loss represents the 

 carbonic acid absorbed. 



As the process is conducted in a jar of known capacity, 

 it is simple to calculate the amount for every 1,000 volumes 

 of air in the building. 



This process, known as Pettenkofer's, requires some 

 training in volumetric analysis, the difficulties attached 

 to it may be overcome by the employment of Angus Smith's 

 test, which is a rough method but capable of yielding fairly 

 accurate results, and is worked on the principle of the 

 turbidity produced in lime water by the presence of carbonic 

 acid. 



Into a certain number of bottles of known capacity half 

 an ounce of clear lime water is introduced, the air in the 

 bottle is shaken with the lime water, beginning with the 

 small bottles and gradually working up to the larger ones. 

 That bottle in which the first visible turbidity appears is 

 the one accepted as representing the amount of carbonic 

 acid present. 



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