700 POPULAR SCIENCE MONTHLY. 



of the larger size an expansion ratio in the turbines of one hundred- 

 fold and upward is attained before the steam passes to the exhaust 

 pipe and condenser. 



The loss of power present in engines of the piston class, due to 

 cylinder condensation arising from the variation of steam pressure 

 in the cylinder, is not present in the steam turbine, as the steam 

 pressure remains constant at each turbine ring and each part of the 

 cylinder and barrel, and the numerous tests of steam consumption 

 that have been made have shown that compound steam turbine 

 engines of moderate sizes when working with a condenser are com- 

 parable in steam consumption per effective horse power with the 

 best compound or triple condensing steam engines of the piston 

 type. They have been constructed in sizes up to about one thou- 

 sand horse power for driving alternators and dynamos, and several 

 sets of about two thousand horse power are nearing completion. 



The application of the compound steam turbine to the propul- 

 sion of vessels is a subject of considerable general interest, in view 

 of the possible and probable general adoption of this class of engine 

 in fast vessels. 



In the turbine is found an engine of extremely light weight, 

 with a perfectly uniform turning moment, and very economical in 

 steam in proportion to the power developed, and, further, it can be 

 perfectly balanced so that no perceptible vibration is imparted to 

 the ship. The problem of proportioning the engine to the screw 

 propellers and to the ship to be driven has been the subject of 

 costly experiments extending over several years, with the result 

 that a satisfactory solution has been found, giving very economical 

 results in regard to pounds of steam consumed in the engines per 

 effective horse power developed in propelling the vessel, results 

 which are equal or superior to those so far obtained with triple- 

 expansion engines of ordinary type in torpedo boats or torpedo- 

 boat destroyers. The arrangement adopted may be best described 

 by saying that instead of placing, as usual, one engine to drive one 

 screw shaft, the turbine engine is divided into two, three, or some- 

 times more separate turbines, each driving a separate screw shaft, 

 the steam passing successively through these turbines; thus when 

 there are three turbines driving three shafts, the steam from the 

 boiler passes through the high-pressure turbine, thence through 

 the intermediate, and lastly through the low, and thence to the 

 condenser. 



As to the propellers, these approach closely to the usual form. 

 It has, however, been found best to place two propellers of approxi- 

 mately the same pitch on each shaft at some considerable distance 

 apart, so that the after one shall not be seriously affected by the 



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