PROBLEM 172 



197 



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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 (ff), 

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

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

 pump (if). From here it is returned through pipe (i) to (JW), where any deficiency 

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

 through the regulating pans (A^", AO 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 



