exhaust chamber might appear at first thought to be a great loss of kinetic energy, but, as has been previously stated, the static energy in the steam as it enters the nozzles is converted into kinetic energy by its passage through the divergent nozzles, and the result is a greatly increased 'volume of steam leaving the nozzles at a tremendous velocity, but at a greatly reduced

pressure practically exhaust pressure-impinging against the buckets of the turbine wheel and thus causing it to revolve.

Efficiency tests of the De Laval turbine show a high economy in steam consumption, as, for instance, a test made by Messrs. Dean and Main of Boston, Mass., on a 300 H. P. turbine, using saturated steam at about 200 lbs. pressure per sq. in. and developing 333 Brake

H. P., showed a steam consumption of 15.17 lbs. per B. H. P., and the same machine, when supplied with superheated steam and carrying a load of 352 B. H. P., consumed but 13.94 lbs. per B. H. P. These results compare most favorably with those of the highest type of reciprocating engines.

Fig. 150 shows a cross section of a 300 H. P. De Laval wheel, showing the design necessary for withstanding the high centrifugal stress to which these wheels are subjected. All De Laval wheels are tested to withstand the centrifugal stress of twice their normal velocity without showing signs of fatigue.

The following table gives the sizes and weights of some of these turbines, together with revolutions per minute of the turbine shaft and the main shaft.

DISPOSAL OF THE EXHAUST STEAM OF STEAM TURBINES

Advantages of exhausting into a condenser-Possible to maintain higher vacuum in condenser of a turbine than with reciprocating engine-Surface condensers-Bulkley injector condenser -Steam turbine condensing apparatus at St. Louis Exposition, 1904-Dry air pump-Gain in economy from high vacuumCost of operating auxiliaries-Necessity of excluding all air from condensing system-Ways in which air may be entrained-Comparative efficiency of turbines and reciprocating engines Percentage of saving per each inch increase in vacuum above 25 inches-Advantages of superheating the steam-Outlook for future of steam turbines.

As in the case of the reciprocating engine, the highest efficiency in the operation of the steam turbine is obtained by allowing the exhaust steam to pass into a condenser, and experience has demonstrated that it is possible to maintain a higher vacuum in the condenser of a turbine than in that of a reciprocating engine. This is due, no doubt, to the fact that in the turbine the steam is expanded down to a much lower pressure than is possible with the reciprocating engine.

The condensing apparatus used in connection with steam turbines may consist of any one of the modern improved systems, and as no cylinder oil is used within the cylinder of the turbine, the water of condensation may be returned to the boilers as feed water. If the condensing water is foul or contains matter that would be injurious to the boilers, a surface condenser should be used. If the water of condensation is not to be used

in the boilers, the jet system may be employed. Another type of condenser that is being successfully used with steam turbines is the Bulkley injector condenser.

Among the steam turbines that were on exhibition at the St. Louis exposition in 1904 the WestinghouseParsons and the General Electric Curtis turbines were each equipped with Worthington surface condensers, fitted with improved auxiliary apparatus consisting of dry vacuum pumps, either horizontal of the well-known Worthington type, or rotative motor-driven, a hot well pump, and a pump for disposing of the condensed steam from the exhaust system. The two latter pumps were of the Worthington centrifugal type. The Hamilton-Holzwarth turbine was equipped with a Smith-Vaile surface condenser, fitted with a duplex double-acting air pump, a compound condensing circulating pump, and a rotative dry vacuum pump, motor-driven. The vacuum maintained was high, 28 to 28.5 in.

As an instance of the great gain in economy effected by the use of the condenser in connection with the steam turbine, a 750 K. W. Westinghouse-Parsons turbine, using steam of 150 lbs. pressure not superheated and exhausting into a vacuum of 28 in., showed a steam consumption of 13.77 lbs. per B. H. P. per hour, while the same machine operating non-condensing consumed 28.26 lbs. of steam per B. H. P. hour. Practically the same percentage in economy effected by condensing the exhaust applies to the other types of steam turbines.

With reference to the relative cost of operating the several auxiliaries necessary to a complete condensing outfit, the highest authorities on the subject place the

power consumption of these auxiliaries at from 2 to 7 per cent of the total turbine output of power. A portion of this is regained by the use of an open heater for the feed water, into which the exhaust steam from the auxiliaries may pass, thus heating the feed water and returning a part of the heat to the boilers.

A prime requisite to the maintenance of high vacuum, with the resultant economy in the operation of the condensing apparatus, is that all entrained air must be excluded from the condenser. There are various ways in which it is possible for air to find its way into the condensing system. For instance, there may be an improperly packed gland, or there may be slight leaks in the piping, or the air may be introduced with the condensing water. This air should be removed before it reaches the condenser, and it may be accomplished by means of the "dry" air pump.

This dry air pump is different from the ordinary air pump that is used in connection with most condensing systems. The dry air pump handles no water, the cylinder being lubricated with oil in the same manner as the steam cylinder. The clearances also are made. as small as possible. These pumps are built either in one or two stages.

A barometric or a jet condenser may be used, or a surface condenser. The latter type lessens the danger of entrained air, besides rendering it possible to return the condensed steam, which is pure distilled water, to the boilers along with the feed water, a thing very much to be desired in localities where the water used for feeding the boilers is impregnated with carbonate of lime or other scale-forming ingredients.

In comparing the efficiency of the reciprocating engine and the steam turbine it is not to be inferred