THE CALORIMETER. 47 



than does the metallic surface of the copper. The chief value of the deter- 

 mination of the water vaporized inside of the chamher during an experi- 

 ment lies, however, not in a study of the vaporization of water as such, but 

 in the fact that a certain amount of heat is required to vaporize the water 

 and obviously an accurate measure of the heat production must involve a 

 measure of the amount of water vaporized. So far as the measurement of 

 heat is concerned, it is immaterial whether the water is vaporized from the 

 lungs or skin of the subject or the clothing, bedding, or walls of the cham- 

 ber; since for every gram of water vaporized inside of the chamber, from 

 whatever source, 0.586 calorie of heat must have been absorbed. 



The apparatus as perfected is very sensitive. The sojourn in the chamber 

 is not uncomfortable; as a matter of fact, in an experiment made during 

 January, 1909, the subject remained inside of the chamber for 30 hours. 

 With male patients no difficulty is experienced in collecting the urine. No 

 provision is made for defecation, and hence it is our custom in long experi- 

 ments to empty the lower bowel with an enema and thus defer as long as 

 possible the necessity for defecation. With none of the experiments thus 

 far made have we experienced any difficulty in having to remove the patient 

 because of necessity to defecate in the cramped quarters. It is highly prob- 

 able that, with the majority of sick patients, experiments will not extend 

 for more than 8 or 10 hours, and consequently the apparatus as designed 

 should furnish most satisfactory results. 



In testing the apparatus by the electrical-check method, it has been found 

 to be extremely accurate. When the test has been made with burning alco- 

 hol, as described beyond, it has been found that the large amount of mois- 

 ture apparently retained by the white enamel paint on the walls vitiates 

 the determination of water for several hours after the experiment begins, 

 and only after several hours of continuous ventilating is the moisture con- 

 tent of the air brought down to a low enough point to establish equilibrium 

 between the moisture condensed on the surface and the moisture in the air 

 and thus have the measured amount of moisture in the sulphuric acid 

 vessels equal the amount of moisture formed by the burning of alcohol. 

 Hence in practically all of the alcohol-check experiments, especially of 

 short duration, with this calorimeter, the values for water are invariably 

 somewhat too high. A comparison of the alcohol-check experiments made 

 with the bed and chair calorimeters gives an interesting light upon the 

 power of paint to absorb moisture and emphasizes again the necessity of 

 avoiding the use of material of a hygroscopic nature in the interior of an 

 apparatus in which accurate moisture determinations from the body are to 

 be made. 



The details of the bed calorimeter are better shown in fig. 4. The open- 

 ing at the front is here removed and the wooden track upon which the 

 frame, supporting the cot, slides is clearly shown. The tension equalizer 



