158 A RESPIRATION CALORIMETER. 



changes taking place in the water content of the body be stated accu- 

 rately. It is evident further that inasmuch as it is impossible to dis- 

 tinguish between water in the body of the subject and the water on the 

 bedclothes, it is useless to weigh the bedclothes any more accurately 

 than the weight of the man's body can be obtained, and also useless to 

 provide for the weighing of the bedclothes if the man's body can not 

 be weighed. 



In the earlier experiments we endeavored to weigh the subject by 

 means of a platform balance ; but though the balance was extremely 

 sensitive when standing on the laboratory floor, it was found that when 

 placed inside of the calorimeter chamber the inequalities of the floor 

 surface were such as to make accurate weighing practically impos- 

 sible, though probably the error was not greater than 100 to 200 grams 

 under the most favorable circumstances. 



Description of weighing apparatus. In considering any method for 

 weighing the subject inside the chamber, it was seen that, to be of 

 any value, the weights should be accurate to at least within 5 grams, 

 since 5 grams would correspond to the weight of about 3 liters of oxygen. 

 Furthermore, the weighings must be carried out fairly rapidly, and what- 

 ever apparatus was used must be capable of sustaining a weight equal 

 to that of the body of the subject. It was, moreover, deemed highly 

 important to devise a method by which all of the weighings could, if 

 possible, be made outside of the respiration chamber, where the weights 

 could be properly checked by a second observer. 



The space between the ceiling of the laboratory and the top of the 

 calorimeter is small, but it was possible, by going to the floor above 

 and cutting through the ceiling, to arrange a platform balance imme- 

 diately over the center of the top of the chamber. A hole was then cut 

 straight down through both top panels of the calorimeter and through 

 the double wall of the metal chamber, and through this an apparatus 

 was arranged for suspending objects within the chamber from the plat- 

 form scale. The arrangement of the apparatus is shown in figure 46. 



A copper shoulder, threaded on the inside, was securely soldered to the 

 copper wall of the chamber. A long fiber tube was screwed into this 

 wall and thus gave an opening in the wall through which could pass 

 vertically a cord or rod on which the object to be weighed could be 

 suspended. To make the opening continuous to the upper side of the 

 ceiling of the calorimeter laboratory, the fiber tube was lengthened out 

 by screwing a brass tube to its end. This gave a straight opening, 30 mm. 

 in diameter, from the floor above down into the calorimeter chamber. 

 It was well adjusted in a vertical position and thus permitted the suspen- 

 sion of a weight by a rod without having the rod touch the sides of the 

 tube. 



