272 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1912. 



profited by the substitution of turbines for piston engines in the 

 construction of marine engines provided with superheating. The 

 use of superheating is here made possible by the suppression of the 

 lubricatmg oil which, when mixed -with the steam, after passing 

 through the boUer is apt to decompose m the superheater and cause 

 trouble. Precautions are necessary that the superheater is not 

 burned up when its supply of steam decreases too much or ceases. 

 To avoid this, Yarrow pro\aded a way of diverting by a damper more 

 or less of the hot gas from the lire. This damper is cooled by a current 

 of air passing constantly between its faces to prevent their deforma- 

 tion. An economy of 10 to 12 per cent was thus obtained with a 

 superheating of 50° to 65°. 



The celebrated electrician, Tesla, has invented a steam turbine 

 wliich seems to possess the greatest possible simphcity. It consists 

 of a series of disks fastened to the same shaft and inclosed within a 

 common casing. The steam, admitted tangentially into the casing, 

 after describing spirals in contact mth eaoli of the disks, escapes 

 through a central opening. The friction thus produced suffices to give 

 a very rapid rotation. With disks 457 milfimeters in diameter and 

 25 in number and steam at 9 Idlograms, experiments made at New 

 York developed a speed of 9,000 turns per minute and a horsepower 

 of 200. The steam consumption, as might have been expected, was 

 unfortunately very great. It reached 17 Idlograms of steam per 

 horsepower. The inventor hopes to get greater economy through 

 the use of condensation. But it is doubtful whether the driving of 

 the disks by friction of the steam, wliich is the main point of tliis 

 invention, will ever give good results as to steam consumption. Ilis 

 system has the advantage of allowing easy reversal. Two jets, enter- 

 ing in opposite directions, are all that is necessary, employing one for 

 the forward, the other for backward motion. 



An attempt was made with the same turbine to use gas burning 

 under pressure after ha-sdng been mixed with sufficient water to render 

 the temperature harmless. The results were not stated. 



II. GAS AND PETROLEUM ENGINES. 



The gas engine, despite the conveniences in its use, did not reach its 

 full development the day that cheaper gases were substituted for the 

 more expensive illuminating gas. 



The most common process of producing tlxis cheaper gas consists in 

 passing a current of air over a column of the combustible, raised to a 

 red heat over some 70 centimeters; the combustible part of the gas 

 thus obtained is an oxide of carbon. In place of dry air, moist air is 

 often injected. The water dissociates, furnisliing hydrogen wliich 

 combines with the carbon and oxygen, wliile the water at the same 

 time lowers the temperature of the apparatus. Tliis gas producer is 



