16 UNIV. OF N. H. AGR. EXPERIMENT STATION [Bulletin 240 



Pump for Aliquot Air Sample 



In addition to this system of collecting the carbon dioxide for weighing, 

 another and still simpler system for determining the oxygen deficit and the 

 carbon dioxide increase of chamber air is now being tried out on the large 

 respiration apparatus simultaneously with the absorber method. (See 

 Plates 2 and 5.) This consists simply of an air-tight pump which collects 

 an aliquot air sample for the period of the experiment. The pump is 

 actuated by an electro-magnet, which is timed by one of the meters that 

 record the amount of ventilation. The use of this pump eliminates all the 

 absorbers for carbon dioxide and water vapor and thus eliminates much 

 work in weighing. It involves of course several additional gas analyses, 

 but the amount of time and expense saved by this procedure promises a 

 great advance in method. If meters of sufficient size to take the whole 

 ventilating current are used, then the aliquoting of the air current may 

 also be dispensed with on the large chamber for cattle. On the small 

 chambers for sheep this method of measuring the total air is now followed 

 entirely. 



Operation of the Respiration Apparatus 



The technical object of a respiration experiment is, as has been stated, 

 to measure the amount of oxygen the animal absorbs and the amount of 

 carbon dioxide it eliminates during a given time, generally during 24 hours. 

 The period may, however, be shorter, provided it permits calculating the 

 true 24-hour equivalent. The measurement of the amount of oxygen 

 consumed and of carbon dioxide excreted by the animal during the period 

 of the experiment thus involves determination of the following conditions : 



1. Composition of chamber air at start. 



2. Volume of outdoor air entering chamber. 



3. Composition of outdoor air.^ 



4. Volume of air withdrawn from the chamber. 



5. Composition of chamber air at end. 



6. Composition of aliquot air sample.^ 



7. Chamber temperature, wet and dry bulb. 



8. Barometer pressure. 



Ventilation 



The volume of ventilation is measured by meters which record the 

 amount in liters, the air removed from the chamber being passed through 

 two meters set in tandem for this purpose. The object of using dupHcate 

 meters is to serve as a check, both on the accuracy of meters and of reading 

 the meters. The volume of in-going air must be proportional to the 

 amount withdrawn, as withdrawal would otherwise create a vacuum which is 

 impossible with the conditions supplied by the inside door. (See page 12.) 



Since the animal consumes oxygen and excretes carbon dioxide, the air 

 in the chamber is being altered as soon as the doors are closed. The com- 

 position of outdoor air is constant, that is, it contains 20 940 per cent of 

 oxygen and 0.030 per cent of carbon dioxide. If the ventilating motors 



1 As the percentage of oxygen and of carbon dioxide in outdoor air is constant these 

 determinations are made only to test efficiency of gas analysis apparatus itself. 



2 Necessary only when no absorbers are used. 





