PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 351 



heat used in superheating steam have done the work of 1,000 units used 

 upon water; heat goes four times farther on steam than on water. 



If waste heat is used for superheating the steam to *I12*^, we double our 

 power without increased cost for fuel; or, if the heat costs at the same rate 

 as when used in water, we double power at an additional outlay of 25 per 

 cent. I7i the first case, we realize a total gain of 50 per cent., and in 

 the second, of 37| per cent. But, unfortunately, it is not yet practicable 

 to use steam at a temperature so high as 712°; the materials we use about 

 our engines will not endure it; we can, however, practically use steam at 

 about 400°, and thus realize an economy as high as 25 per cent. 



Superheated steam is now much used in chemical operations, as a con- 

 venient means of heating, and to effect certain decompositions. Superheated 

 steam upon iron, at a red heat, gives its oxygen to the iron and its hydrogen 

 escapes; upon carbon, at a white heat, its oxygen unites with the carbon 

 to form carbonic oxyd and carbonic acid, and the hydrogen is set free; upon 

 metallic sulphides, the hydrogen unites with the sulphur to form sulphide 

 of hydrogen, and the oxygen with the metal ; upon oils, when the fat acid 

 is separated from the glycerine, &c., &c. 



Mr. Rowell. — I hold in my hand a table of the observations made at one 

 of the series of experiments which were tried at the Metropolitan mills in 

 this city, in 1860, to test the value of superheating steam and of working 

 steam expansively. These experiments were made under the direction of 

 B. F. Isherwood, now engineer-in-chief of the United States Navy, at a 

 cost of about $5,000, which was paid by Mr. George Hecker. They were 

 commenced on the 1st of February, and finished on the 1st of November. 

 An engine was constructed expressly for the purpose, and it was the first 

 time in the history of the steam engine, in which an engine was made for 

 the single purpose of testing questions in regard to its operation. The fuel 

 and water of condensation were carefully weighed, and the temperature 

 and pressure of the steam in all parts of the apparatus, as well as the 

 temperature of the room, the barometric pressure, the temperature of the 

 feed water, and, in short, all circumstances that could affect the result, were 

 carefully observed and recorded every hour. It was the most valuable, as 

 well as the most costly, series of experiments that have ever been made in 

 regard to the practical working of steam. 



The plan of superheating was to surround the cylinder with a steam 

 jacket, and then throttle the steam in the cylinder, so as to reduce its pres- 

 sure without diminishing its temperature. It was found that there was no 

 marked economy in superheating more than 5°. At this extent of super- 

 heating, the economy was 54 per cent.; that is to say, 46 pounds of coal, 

 with this method of superheating, did as much work as 100 pounds of coal, 

 with steam used in the ordinary way. 



Mr. Dibben. — I introduced this question with an idea that the facts 

 brought out would show that the prejudice against superheated steam is 

 not well founded, and the discussion has fully sustained my opinion. The 

 statement of Mr. Babcock shows that if a superheater is properly con- 

 structed, there is no burning out of the tubes, about which we have heard so 

 much, and the working of Ericsson's air engines proves conclusively that lubri- 

 cating materials will bear a temperature of 450° without being decomposed. 



