79 



pressure was varied by the use of the upper valve, throttling- the up- 

 stream section. In this way up-stream pressures of from 40 pounds per 

 square inch down by 5 five pounds per square inch steps to the lower 

 limit were effected. The apparatus discharged into a weighing tank and 

 the discharge was weighed. The temperature of the water was taken 

 every minute because this temperature varied greatly throughout the tests, 

 due to the fact that the standpipe tank was connected to the condenser 

 of a Corliss engine. (With respect to the effect of the temperature on the 

 results, it may be said that when the temperature of the discharge rose 

 above the 100° F., the tail pressure gauge showed a very unsteady pres- 

 sure, the needle vibrating with a range of as much as one-half pound. 

 The disc was no doubt at this time subject to vibrations, which, when 

 the temperature of the water rose to 110° F., were of such frequency as 

 to cause a musical note. Under the latter condition the needle was too 

 sluggish to respond and remained at a fixed position. The movement is 

 probably connected with alternate periods of vaporization and condensa- 

 tion of the AA'ater on tlie upper side of the disc.) 



Results. — The following combinations of nozzle and disc wei'e used: 

 One-eighth-inch nozzle, 1-inch disc; i/8-i"t'li nozzle, li/4-inch disc; %-irich 

 nozzle, 2-inch disc; 3-ltJ-inch nozzle, 1-inch disc; 3-16-inch nozzle, 1%-inch 

 disc; 3-16-inch nozzle, 2-inch disc; Vrincli nozzle, 1-inch disc; 14-inch noz- 

 zle, IJ/Mnch disc; i/4-inch nozzle, 2-inch disc. 



Of these, the i4"i"<'li nozzle gave successful results; the 14-inch nozzle, 

 with the 2-inch disc, gave the best results. These are shown in Fig. 4. 

 In working the head pressure down toward the tail pressure the former 

 would approach a critical point at which the difference of pressure became 

 so slight that the regulating effect ceased and both head and tail gauges 

 suddenly moved to the same reading. The disc at this period, no doubt, 

 dropped away from the .let. That is a certain diffei-ence of pressures is 

 needed to enable the apparatus to work. This difference of pressure be- 

 came greater as the tail pressure was increased, as is shown in Fig. 4. 



In experiments with the other orifices mentioned the lines shown in 

 Fig. 4 became straight lines inclined to the horizontal. The hump in Fig. 4 

 was characterized by an unsteady head pressure. 



One disc was bevelled so as to give a constant area of passageway to 

 the expanding ring of water, that is, it was dished with the deepest 

 part next to the nozzle. This disc preserved a constant difference of pres- 

 sure between the head and tail pressures. 



