GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 69 



ber can be measured by this method within 70 cubic centimeters. Even 

 in experiments of but an hour's duration, where the amount of oxygen 

 admitted from the cylinder is but 25 to 30 grams, it can be seen that the 

 error in the weighing of the oxygen is much less than 1 per cent. 



The earlier forms of cylinders used were provided with valves which 

 required some special control and a rubber bag was attached to provide 

 for any sudden rush of gas. The construction of the valve and valve-stem 

 was unfortunately such that the well-known reduction valves could not 

 be attached without leakage under the high pressure of 120 atmospheres. 

 With the type of cylinder at present in use, such leakage does not occur and 

 therefore we simply attach to the oxygen cylinder a reduction-valve which 

 reduces the pressure from 120 atmospheres to about 2 or 3 pounds to the 

 square inch. The cylinder, together with the reduction valve, is suspended 

 on one arm of the balance. The equipment of the arrangement is shown 

 in fig. 31. (See also fig. 5, page 4.) The cylinder is supported by a 

 clamp K hung from the balance arm, and the reduction-valve A is shown 

 at the top. The counterpoise S consists of a piece of 7-inch pipe, with 

 caps at each end. At a convenient height a wooden shelf with slightly 

 raised rim is attached. 



In spite of the rigid construction of this balance, it would be detrimental 

 to allow this enormous weight to remain on the knife-edges permanently, so 

 provision is made for raising the cylinders on a small elevator arrangement 

 which consists of small boxes of wood, T, into which telescope other boxes, 

 T'. A lever handle, E, when pressed forward, raises T' by means of a 

 roller bearing U, and when the handle is raised the total weight of the 

 cylinders is supported on the platforms. 



The balance is attached to an upright I-beam which is anchored to the 

 floor and ceiling of the calorimeter laboratory. Two large turnbuckle eye- 

 bolts give still greater rigidity at the bottom. The whole apparatus is 

 inclosed in a glass case, shown in fig. 5. 



AUTOMATIC CONTROL OF OXYGEN SUPPLY. 



The use of the reduction-valve has made the automatic control of the 

 oxygen supply much simpler than in the apparatus formerly used. The 

 details of the connections somewhat schematically outlined are given in 

 fig. 32, in which D is the oxygen cylinder, K the supporting band, A the 

 reduction-valve, and J the tension-equalizer attached to one of the calo- 

 rimeters. Having reduced the pressure to about 2 pounds by means of 

 the reduction-valve, the supply of oxygen can be shut off by putting a 

 pinch-cock on a rubber pipe leading from the reduction-valve to the calo- 

 rimeters. Instead of using the ordinary screw pinch-cock, this connection 

 is closed by a spring clamp. The spring E draws on the rod which is con- 

 nected at L and pinches the rubber tube tightly. The tension at E can be 



