22 A RESPIRATION CALORIMETER. 



inner walls of the pipe is filled with mercury which flows down from 

 above through the small holes o and o l . This column of mercury 

 is approximately 100 mm. long, and its pressure, increased by the 

 50 mm. pressure of the air current, tends to force the mercury against 

 the packing at the bottom and thus prevent the entrance of air. 

 The valve is constructed of a 2-inch T, which is galvanized on the 

 outside to fill possible blow-holes in the iron. Before galvanizing, 

 the ends of the T were plugged to prevent the zinc entering the inner 

 part and subsequently forming an amalgam. A reducer, r, is fitted in 

 the top, and a short 2-inch nipple inserted in the lower part. The 

 lower end of the nipple is covered with a cap, q. This cap was made 

 from a special casting, and is provided with a small pipe to which the 

 rubber tube m is attached. The ball and socket joint j minimizes 

 lateral motion and consequent destruction of the fiber gasket g. The 

 pipe b, which is screwed into the reducer r, has its lower end trued 

 and the edges slightly rounded to prevent cutting the gasket. As is 

 seen in figure 10, the connections from this pipe to both the blower 

 and the absorbers are made with ordinary steam fittings. All the 

 metal work of the valve is of iron or steel. 



When it is desired to open the valve, the reservoir / is lowered, and 

 by reason of the pitch of the under side of the cap q every particle of 

 mercury is drained out of the valve. The valve wheel is then turned 

 and the mechanical closure opened. There is then a free passage for 

 the air through the side tube, around the annular space, and up through 

 the tube b. When the valve is opened the only chances for a leak are 

 around the coupling d and through the stuffing-box n. The coupling 

 d is the same as is used at all other junctions of the absorbing system, 

 and when connected is always specially tested (see p. 32) to insure 

 against leak at this point. The tendency of the mercury is to press 

 out of the stuffing-box n ; consequently no leak has ever been found. 

 When the valve is closed one of the chances for leak is shifted from 

 the coupling d to the closure of the pipe b, for after removal of the 

 water-absorber attached at d the air in the annular space a a is at a 

 pressure of from 30 to 50 mm., while that in b is at atmospheric pres- 

 sure. Because of the mechanical closure on gasket g and the mercury 

 seal, no air can pass from a to b. 



It sometimes happens that the gasket g becomes worn or cut, or that 

 a particle of dust gets in between g and the pipe b, thereby preventing 

 a tight mechanical closure. Under these conditions, unless the column 

 of mercury above the level of g is sufficiently high, there may be a slight 

 leakage of gas down through the mercury into the inside of tube b. 

 This condition is, however, seldom present, and suitable tests for such 

 a leakage have been devised. 



