62 ANNUAL OF SCIENTIFIC DISCOVERY. jp 



mixed with the stoam, and which has been heated at the expense 

 of the fuel? It is tivident that it is useless lor power, and, as it 

 has no latent heat, it is very unavailable for heating or drying 

 purposes. It cannot act otherwise than as a " clog," causing 

 more friction in the sleam l)y its presence, inconveniencing the 

 operation of the engine, and tending to condense the steam with 

 which it is associated. Now, by superheating this wet, saturated 

 steam, it is converted into an elastic vapor, by the complete and 

 instantaneous vajjorization of its surplus moisture, Avhile its tem- 

 perature is raised sullicient to preserve it from premature con- 

 densation in passing to the cylinder, or to the heating or drying 

 coils. The volume and elasticity of the steam is thus increased 

 to a wonderful extent by a very moderate degi'ee of superheat- 

 ing, and its subsequent operation in the cylinder is highly satis- 

 factory. But another advantage in the system should not be 

 overlooked, and that is the expansion of the steam as a gas, by 

 the heat imparted to it after its surplus moisture has been evap- 

 orated. Although the greatest gain must ensue from the addition 

 of the first few degrees (say fifty) of heat, when the expansion of 

 the steam from its previous saturated condition is very great, yet 

 thehighest authorities agree, that, after it is thorougldy dried, the 

 steam follows tlie laws of gases, and its volume may be doubled 

 by the adilition of 4b0 degrees of heat. It is a fact proved by 

 most accurate experiments, that the higher the degree of super- 

 heating, the greater is the economy ; and if steam could l)e used 

 at a tem2>erature of 1,U0U degrees, its elliciency woukl be very 

 largely increased. Inasmuch as it is not practicable or conven- 

 ient with engines, as at present constructed, to use steam at such 

 extreme temperatures, we are unai)le to reahze the greatest econ- 

 omy of superiieating ; but, if ordinary steam of 50 pounds pr(!ssure, 

 at a temperature of 3U1 degrees, be superheated t(j 400, the addi- 

 tion of this 99 degrees of heat will augment its volume (or pres- 

 sure) more than 20 per cent., and will not rend(;r it at all injuri- 

 ous to the lul)rication or jiacking. Where this superheating is 

 effected by the waste products of combustion, the increase re- 

 ferred to is all clear gain ; but when acquired, as is frequently 

 done for convenience, at the expense of the fuel, a simjjle calcu- 

 lation shows that even then the economy from the expansion as a 

 gas is from 10 to 15 per cent., independent from that realized in 

 the vaporization of its surplus moisture, and which is as much 

 more. Saturated steam cannot part with any of its heat without 

 becoming condensed ; and this loss, by premature condensation, 

 is often a very large percentage of the total amount of steam 

 used. In every unit of the steam thus condensed, there are lost 

 1,000 units of heat, whicTi have been sui)plied by the fuel, but 

 have not been utilized. Superheated steam, imder the same cir- 

 cumstances, might lose all of its surplus heat, but would still exist 

 as steam. 



In England, where the practical advantages of superheated 

 steam are more thoroughly understood and generally acknowl- 

 edged, its employment is common, and is attended with the most 

 satisfactory and economical results. The steamers of the " Penin- 



