VI. C A T. O R I INI K T R I C MEASUREMENTS 185 



C. CALORIMETRIC METHODS 



An account of the development of calorimetric methods is found 

 in Saha's treatise {15). A thorough discussion of the present status 

 of the subject is found in a chapter by Sturtevant {16). 



1. Classification and Choice of Calorimeters 



Table II indicates how calorimeters may be classified according 

 to their major characteristics. 



The choice of a calorimetric method may have to be based on cri- 

 teria different from those used in Table II. The magnitude of ther- 

 mal effects may have to be considered. The measurement of a man's 

 rate of heat production requires macrocalorimetry. The study of the 

 heat of setting concrete even in giant dams, on the other hand, may 

 well be accomplished by microcalorimetric methods because the es- 

 sential conditions such as temperature, pressure, and chemical com- 

 position may be adequately reproducible on a small scale. Availabil- 

 ity and cost of equipment, skill, and time necessary for the measure- 

 ment may be other factors involved in the choice of the method. 



Heats of combustion of ordinary plant or animal materials may 

 be accomplished by rather well standardized methods and a number 

 of bomb calorimeters for this purpose are readily available and ade- 

 quately described in the catalogs of the supply houses for laboratory 

 equipment. Even without previous training in physics or chemistry, 

 normally intelligent people can be taught in a few weeks to operate 

 these instruments for satisfactory routine measurements, provided 

 the teacher and supervisor of these technicians has himself sufficient 

 basic knowledge. For such routine measurements by technicians 

 with limited training, a calorimeter jacket with high heat capacit}^ 

 and nearly constant temperature (see Sect. C7) is preferable to the 

 adjustable adiabatic jacket. The three rows of temperature figures 

 obtained mth the constant jacket in the preliminary, main, and after 

 period of the measurement can readily be checked, and irregularities 

 are easily detected, whereas errors in the operation of the adiabatic 

 jacket may be difficult to trace after the measurement is completed 

 (see the last paragraph in Section C7). 



For the measurement of heat exchange during photosynthesis or 

 for animal calorimetry no generally followed routine is established 

 and no standard equipment is available. Good training in physics 

 and rather well developed engineering ability are among the prerequi- 



