748 TRUEBLOOD. 



pipes are in parallel ; in fact, for a considerable area of the (p, T) plane, 

 either velocity is so small, for the highest flow rates used, that the 

 steam could be considered at rest so far as any temperature effect 

 of its kinetic energy is concerned. By altering the connections of the 

 superheater so that the groups of pipes are placed in series instead 

 of in parallel, tests of the effect of different velocities in the super- 

 heater and in the plug case may be made. 



In the operation of the apparatus, it has been customary to bring 

 the steam to a temperature exceeding the high side working tempera- 

 ture by from fi\e to fifteen degrees C, or e\'en more, before it enters 

 the secondary superheater. This superheater thus really acts as a 

 cooler. The chief purpose of this method of operation is to avoid the 

 possibility of the introduction of moisture into the steam by condensa- 

 tion in the short length of heavily lagged pipe connecting the primary 

 superheater {Si, Fig. 5; S, Fig. 6) with the secondary superheater. 

 (The lagging on this pipe is shown in Fig. 6, but is omitted in Fig. 5). 

 A well (ir. Fig. 5) for a mercury thermometer is provided at the 

 entrance of the secondary superheater, to facilitate this regulation of 

 temperature. 



As a further precaution against moisture, the steam passes through 

 a strainer (contained in the chamber M, Figs. 5 and 6) just before 

 entering the secondary superheater, and through another strainer 

 (chamber m, Figs. 5 and 6) just after entering it. These strainers 

 are both of alundum and are, in fact, nothing but small editions of 

 the plug in which the throttling takes place. By omitting either or 

 both, tests of the need for them and of their efficacy may be made. 

 Some remarks and conclusions, from experimental results, on the 

 utility of such strainers will be found in section IV, 2 g, which deals 

 with the data derived from the type U plug case. 



The stirring devices are indicated at P, P, P, p, p, Fig. 5. The 

 three larger four-bladed propellers, P, P, P provide the main circula- 

 tion, which is across the lower four pipes of the superheater, under 

 and around the plug case, and back across the upper four pipes of the 

 superheater. Axial circulation is provided by the two smaller four- 

 bladed propellers p, p. 



2. Boiler, Primary Superheater and Condenser. 



The steam is generated in an 18 inch Stanley automobile boiler 

 {B, Figs. 5 and 6), designed to operate at from 500 to 600 pounds per 

 square inch and tested to 1800 pounds per square inch by hydraulic 



