REVIEW OF FEED- WATER TESTS. 263 



2. The siphon type of condenser, in which the water is sup- 

 plied by gravity, and no air-pump is required. 



3. The siphon condenser, in which the water is supplied by 

 an independent pump. 



4. The jet condenser, with air-pump driven by an indepen- 

 dent engine or other motor. 



In all of these, with the exception of the second, the expen- 

 diture of power or the consumption of steam must be charged 

 against the saving due to condensing. Those that use steam 

 can be arranged to utilize a portion of that steam in cases 

 where the exhaust from the independent engine or pump is 

 carried through a feed-water heater, and the heat returned to 

 the boiler. In test No. 15, which was provided with a jet 

 condenser and direct-connected air-pump, the amount of power 

 used by the air-pump was found to be 1.8% of the working 

 power of the engine. In Engine No. 57, which was pro- 

 vided with a siphon condenser supplied with water by an 

 independent pump, the quantity of steam used by the pump, 

 when exhausting into the condenser, was 6.7% of the total 

 consumption of steam by the- engine. In Engine No. 19, 

 which was provided with a jet condenser operated by an in- 

 dependent steam-driven air-pump, the consumption of steam 

 by the pump when exhausting into the air was 13% of the 

 total quantity used by the engine. In Engine No. 20, which 

 was fitted with a similar condenser, the quantity of steam 

 used by the air-pump when exhausting into the condenser 

 was over 13% of the total quantity. When an independent 

 steam-driven air-pump is used, and the heat of the exhaust 

 steam is returned to the boilers so far as possible by heating 

 the feed-water, it is probable that from one-half to two-thirds 

 of the steam is saved ; and in a case where the air-pump uses 

 12% of the entire quantity, the actual loss of coal due 

 to the air-pump would be not over 4 or 5%. From these 

 considerations it appears that in cases where an air-pump 

 or other condenser pump is required, the percentage to be 

 charged to the condenser on this account is, in the best in- 

 stances, about 2% ; and in cases where the exhaust steam 



