EXPERIMENTAL STUDY OF HEAT LEAKAGE. 751 



type known as 'standard test gauge.' The gauge was calibrated at 

 the company's factory. 



The drop of pressure through the plug is measiu-ed directly on the 

 mercury manometer A G, Figs. 5 and 6. As is indicated in Fig. 6, 

 this manometer is so arranged that all joints are packed against water 

 rather than against mercury. The two vertical glass tubes ^i, h 

 (barometer tubing) extend to the bottom of the separate reservoirs 

 ri, r2. These reservoirs are each filled to about one-fourth of their 

 heights with 500 gms. of mercury. The remainder of the volume of 

 each contains water; the top reservoir rz, Fig. 6, together with the 

 space in the glass tubes above the mercury columns, also contains 

 water. As the figure shows, the reservoirs ri and ro are connected 

 respectively to the high and low sides of the plug by means of flexible 

 copper tubing, through the reservoirs Ri and Ri. The purpose of 

 these latter reservoirs is partly to provide a considerable mass of 

 comparatively cool water, all of which must pass tlirough a constricted 

 passage before any steam can escape, in the e^'ent of the bursting of a 

 glass manometer tube. The time required for blowing out this 

 reserve of water is sufficient to enable the experimenter to close the 

 necessary valves, thus preventing further damage to the manometer 

 or other apparatus near it by reason of the presence of hot steam or 

 hot water. The ' constricted passages ' referred to are at the bottom 

 of each of the reservoirs Ri and R^, where the diameter of the passage 

 is reduced to about 0.04 inch for a length of about 0.25 inch. These 

 constrictions also serve to damp oscillations of the mercury in the 

 manometer tubes. 



A further purpose of the reservoirs R\, R^ is to prevent variations in 

 the amount of water in the connections from the gauge to the plug 

 from affecting the registered pressure difference. Such variations 

 may be due to gradual and undetected condensation or to a sudden 

 change in the pressure difference, which would force the water down 

 in one connection and up in the other, or to other causes. Whatever 

 the origin of these variations, the portion of either connecting passage 

 first affected is that between the oil bath and the reservoirs Ri, Rz; 

 as this part is nearly level, the effect on the registered pressure differ- 

 ence of removing even a large part, or all, of the water in it, is slight. 

 If the change in the amount of water is great enough to extend beyond 

 this portion of the connection, the large area of cross-section of the 

 reservoirs Ri, R^ prevents even a large change in the volume of the 

 contained water from greatly affecting its level. It may be stated 

 that the connections between the plug and the differential gauge 



