[D8805AEU], Letter from Charles Edward Emery to Thomas Alva Edison, July 20th, 1888


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[D8805AEU], Letter from Charles Edward Emery to Thomas Alva Edison, July 20th, 1888

Editor's Notes

"I have realized every little while that I owed you a letter and the reason of it is that in your last you put so hard a one that I did not think I could do any better than I had with the question. As you may have forgotten what you wrote (it being in pencil,) I enclose a copy of the letter and in response would say I have carefully examined my discussion of the subject and I feel that I went as far as it was possible to go with our known information as to the 'specific heat of a fluid its coefficient of expansion by heat and the pressures due to such expansion,' which I stated in my letter of September 5th were essential in a preliminary examination of the problem, yet I can not guess what would be the results with the tremndous pressures you speak of. We certainly could do better than at lower pressures as my letter shows a progressive gain from the pressure of 250 to that of 950 pounds discussed, but I rather suspect we would be beaten in the end much in the same way people have been that have tried to use the vapor of some other fluid than that of water. It takes less heat to vaporize such fluids but they do proportionally less work it seems to me that if we did control water at such enormous pressures at 20,000 to 30,000 pounds per square inch and its specific head did 'diminish enormously' it would have that much less heat to do work with merely by expansion of the fluid though of course more if allowed to flash into steam which takes a different type of apparatus and is not what we were investigating as I take it. Repeating by paraphrasing your last sentence, 'if water could not expand at all its temperature would rise almost as quickly as iron and with very little latent heat' yet because the temperature did raise with very little latent br internal heat there would be very little to do the work with, and as you compared it to iron, you will note in my letter that I make the calculations in relation to iron and get a still lower efficiency than with water, so I really think my first conclusions, to the effect that the most economical thermal engine will not be found in the direction of handling dense materials but on the contrary in the other direction something like you have gone into in your pyromagnetic motor. Independent of the above mechanical considerations which of course have nothing to do with the scientific side of the question arise such as the difficulties of handling fluids at such enormous pressures they being with our present knowledge prohibitory. I am Consulting Engineer of the Pneumatic Dynamite Gun Company and with the best talents they could get, the attempts to practically handle 2500 pounds air pressure with the materials and workmanship available in present shops were so great that they reduced their pressure to 1000 pounds. With dense fluids like water in hydraulic presses, of course higher pressures are carried, but between you and I, is not life a little too short for us to attempt to go so far outside of the beaten track [unclear] to accomplish a result. As a clincher, think again of the force of an explosion supposing a little steam forms with water heated hot enough to maintain a pressure of 20,000 or 30,000 pounds per square inch. ### I admire your pluck and stick-to-itaveness and so hope to hear from you again." Very truly yours, Chas. E. Emery




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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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