480 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



always be obtained from a given amount of evaporation, to an extent 

 wbich is only limited by practical circumstances, which restrain the appli- 

 cation of this expansive principle. 



" Since the cost of producing steam, as a mechanical agent, depends on the 

 quantity of fuel necessary to effect the evaporation of a given volume of 

 water, it follows that all the effect obtained by this principle of expansion 

 is so much power added to the steam without any expense. Its impor- 

 tance will be obvious in the economy of steam power." 



In reply to this theory of expansion, as extracted from these works, I 

 will say that the experience of engineers has never been able to realize the 

 enormous gain which is claimed for il. 



M. M. Regnault, in a set of experiments in regard to the nature and 

 properties of steam, which were autliorized by the French government, and 

 recorded in the London and Edinburgh Philosophical Magazine for August, 

 1854, says: 



" According to the views which I Iiave adopted regarding the generation 

 of power in machines mov«d by elastic fluids, the motive power pi'oduced 

 by the expansion of any elastic fluid is always in proportion to the loss of 

 heat undergone by this fluid in the part of the machine where the power is 

 produced. I have labored to bring together the experimental data by 

 which the theoretical motive power produced by a given elastic fluid 

 which undergoes a certain change of volume, might be calculated; unfor- 

 tunately these data are very numerous, and most of them can only be 

 determined by extremely delicate and difficult experiments." 



So that the statements of Mr. Bourne, before quoted, as to the notorious 

 value of expansion, was not discovered by Mr. Regnault in these his " deli- 

 cate and difScult experiments." 



We shall now endeavor to show why the engineers of the present day 

 do not obtain any of these economical results which are so positively 

 claimed for expansion by the various authors aforementioned, such as 

 Bourne, Lardner, etc. We will take the diagram which Mr. Bourne uses 

 to illustrate expansion, and show from it that the losses that occur in 

 the attempt to use steam expansively ai-e more than is compensated by any 

 gain thus obtained. In the first place the steam doubles its volume at 

 half the pressure. For instance, if we take boiler steam at eighty-five 

 pounds pressure, and expect to double its volume, we must add the atmos- 

 phere to it, which is fifteen pounds more; we then have a total pressure, 

 atmosphere and all, of 100 pounds. Now, if we let 100 pounds represent 

 the steam at the conmiencement of the stroke, and expand it four times, 

 twenty-five pounds total pressure will represent the force at the end of the 

 stroke when cutting off at one-quarter; now fifteen pounds have to be taken 

 off, this being the atmospheric pressure, from the whole length of the 

 stroke, and there are five pounds additional pressure to be subtracted, 

 being the amount of force required to run the engine, so that there are 

 twenty pounds to be deducted from the whole length of the stroke, and the 

 final pressure in the cylinder, instead of being twenty-five pounds, exerts 

 an effective force of only five pounds on the piston, at the end of the 

 stroke, showing that the twenty pounds deducted from the first fifty 

 s quares, as represented in the diagram, would consume only ten squares 



