TESTS OF ACCURACY OF HEAT-MEASURING APPARATUS. 169 



are here recorded under the designation R. Occasional readings of S, 

 giving normal or standard deflections of the galvanometer, are here 

 given, and any additional observations of the assistant, particularly as 

 to the movements of the subject, are here briefly stated. 



The heat sheet therefore serves as a source of original data regarding 

 the gain or loss of heat through the walls, the maintenance of constant 

 temperature, the estimation of the heat brought away by the water cur- 

 rent, the body temperature, and the more important movements of the 

 subject. 



TESTS OF THE ACCURACY OF THE HE AT- MEASURING APPARATUS. 



For testing the accuracy of the calorimetric features of the apparatus 

 two special forms of test have been devised. In one a definite amount 

 of heat is generated inside the chamber by means of the passage of an 

 electric current through a known resistance. Knowing the strength of 

 current and the fall of potential, it is possible to calculate accurately 

 the quantity of heat thus developed and compare it with that brought 

 away by the water current. These tests are called electrical check 

 experiments. 



A second test is obtained by burning known weights of ethyl alcohol 

 inside the calorimeter and measuring the energy thus produced. From 

 the weight of the alcohol and the heat of combustion as determined by 

 the bomb calorimeter it is possible to compute the amount of heat which 

 theoretically should be developed and compare it with that brought 

 away by the water current. These are called alcohol check tests. 



ELECTRICAL CHECK TESTS. 



The development of a known amount of heat by means of the electric 

 current necessitates an accurate knowledge of four factors : First, the 

 strength of current; second, the fall of potential; third, the time in 

 seconds, and fourth, the factor for the conversion of electric units 

 to that of heat. Of these four factors we have to consider only those 

 of the strength of electric current, fall of potential, and the conversion 

 factor. The strength of the current in these experiments was deter- 

 mined by passing it through a milli-ammeter, which was especially 

 calibrated for us by the Weston Electrical Instrument Company, of 

 Newark, New Jersey, and guaranteed by them to give readings within 

 o.i per cent. In this instrument the maximum current that could be 

 measured was 1.5 amperes. The instrument has been compared from 

 time to time with a Kelvin balance with no noticeable variations in 

 accuracy. 



