PROBLEM 172 



197 



In order to assure accurate work on the respiratory products, the system of 

 ventilation is also a closed one. The vitiated air is drawn out by the pipe (H), 

 and then through a double row of vessels of sulphuric acid (/, J, J, J) to remove 

 water vapor, and vessels of soda lime (/, /, J, J) to remove CO2, to the electric 

 pump (K). From here it is returned through pipe (L) to (M), where any deficiency 

 in oxygen is noted and remedied from a tank of that gas before it is pumped 

 through the regulating pans (N, N) into the chamber. 



Method. — Using the diagram and explanation, try to explain 

 to your own and your teacher's satisfaction the working of the 

 Atwater calorimeter. 



Conclusion. — What is the practical value of the apparatus? 



Problem 172: To find the value of food as a tissue builder 

 compared with its cost. 



Method. — Use the tables on pages 198-201 ; make sure you 

 understand the various column headings. 



NOTE. — Foods may be considered cheap if they furnish more than .12 of a 

 pound of protein (the tissue builder) for 10 cents at present prices ; medium priced 



