MERCURY MANOMETER 



37 



Fig. 6. Mercury manometer and signal magnet. The arrangement of the tubing 

 (M) connecting the pressure bottle (R) and the arterial cannula (and washout, P, U, 

 V, W) to the manometer is also shown. The pressure bottle should be (adjustably) 

 suspended about four or live feet above the taole by means of a small rope (T) passing 

 through a pulley (S) on the ceiling. A. pointer of signal magnet B, which can be 

 made of a Harvard signal magnet. The rod of the signal magnet has been cut off and 

 bent to pass down (adjustably) into the hole bored in the upper end of the manometer 

 board (H) at K. C. writing point of D, the aluminum wire (No. 18) attached to the 

 manometer plunger E, to the lower end of which the float F, is attached. The inner 

 diameter of the glass tube TV, should be slightly greater than one-fourth inch and the float 

 is made (one inch long) from a one-fourth inch polished hard rubber rod. The lower 

 end of the float is bored out with a 3/16 inch drill to float (full of air) on the surface 

 of the mercury G. Polished drill rod steel (1/32 inch in diameter) is used for the 

 plunger which is driven into a small drill hole in the upper part of the float. /, sup- 

 porting rod of the manometer. /, glass T-tube connected by rubber tubing ( Y) to the 

 right limb of the U-tube. L, adjustable brass (or iron) wire ( ! s inch) from which a 

 thread (Z) supports a small weight to hold the writing point on the drum. O, O, 

 wires running to the signal magnet base line marker (B) from X, X, binding posts 

 which receive electric impulses from the time clock. It is better but more difficult and 

 expensive for the U-tube to have a side outlet blown on the right hand limb in place 

 of the T-tube here shown. The left hand limb of the U-tube should be twelve inches 

 long. A little oil is placed around the float. The U-tube and T-tube are attached to 

 th board by copper wires passed through holes and twisted together behind the board. 



