580 JOHN E. MURLIN 



I was 2.1 amperes. The fall of potential across the terminals of the heat- 

 ing coil was 5.79 volts and the time for each period was 3500 seconds. 

 The heat is given by the product E. I. t X 0.2393 == 10,470. This is 

 expressed in small calories and is equal to 10.47 large calories. The fol- 

 lowing is a tabulation of this experiment. 



TABLE 10 



The advantage of this sort of a check experiment is that the measure- 

 ments can be made very accurately, rapidly and in short periods. It is 

 customary in making such checks to place the resistance coil in the calo- 

 rimeter and make the connections. The current is then passed through the 

 coil and simultaneously the water is started flowing through the heat ab- 

 sorbing system and the whole calorimeter is adjusted in temperature 

 equilibrium. As soon as possible when the temperature of the air 

 and walls is constant and the thermal junction system in equilib- 

 rium, the exact time is noted, and the water current is deflected into the 

 water meter. At the end of thq first hour, the usual length of a period, 

 the water current is deflected from the meter, the water weighed and the 

 average temperature difference of the water is obtained by averaging the 

 results of all the temperature readings during the hour. Usually during 

 an experiment of this nature records of the water temperature are made 

 every four minutes. Occasionally, when the fluctuations are somewhat 

 greater than usual, records are made every two minutes. Tests with the 

 chair calorimeter of the Nutrition Laboratory made in January, 1909, 

 show between the heat developed inside the apparatus in the electric coil 

 and the heat as measured by the water current with corrections a discrep- 

 ancy of about 0.5 per cent (Benedict and Carpenter (a.))- A series of 

 electric checks made upon the Sage calorimeter by the same method shows 

 a total error for the entire series of less than 0.4 per cent (Riche and Sod- 

 er strom). 



Another method of checking the heat measuring capacity of the calo- 

 rimeter is known as the "alcohol check." In this method alcohol is burned 

 inside the apparatus by means of a small alcohol lamp, the rate of flow 

 of the alcohol being made as nearly constant as possible and the amount 

 consumed in a period of observation being carefully recorded upon a finely 

 graduated burette or by weighing. In planning such a test to ascertain the 

 magnitude of the errors which are likely to occur in using the apparatus 

 with subjects of known size it is of importance to provide that the amount 

 of alcohol consumed per hour shall be enough to dissipate approximately 



