Thomas Jefferson Papers

Enclosure: Description of a Steam Engine, 4 June 1800

Description of a Steam Engine

Description of mercurial engine

The figure represents an engine intended to work with very little friction. It must be observed that in order to simplify the drawg an ejection cock on the old principle is substituted for an air pump & condenser which however is to be preferred in practice—Nor can the enjection be made in the manner shewn in the drawing without a snifting valve for each side of the piston to carry off the air & water that would lodge above the mercury but as the object is only to shew the principle of the machine these are omitted

Mercury will rise by the ordinary pressure of the atmosphere if that pressure is taken from its upper surface, about 30 inches   If then a tube of sufficient length closed above was imersed in mercury to the depth of 30 inches, the quicksilver would stand at that hight on both sides of the tube: but if a vacuum was made within, It would then stand 30 inches higher within than without the tube as in the barometer. The mercury would then fall 15. inches without & rise as many within the tube or in other words would be 45 inches high within & 15 inches on the outside, in this case the tube might be raised 15 inches that is to the level of the external mercury before any air could pass into the tube. If this tube was covered by another, when a vacuum was made between them, the mercury would return to its original level [but if] the atmosphere is introduced into the inner tube, while the vacuum exists between the tubes, the position of the mercury would be reversed, & would stand 45 inches high between the tubes & only 15 in the inner one—The inner tube would then be pressed up with the whole weight of the atmosphere till it had risen so high as to let the air pass from one side to the other, so as to restore the equilibrium—

This principle being esstablished, a bare inspection of the drawing (which is a section of the engine) will explain the nature of the machine. a. Is a block of wood of not less than 48 inches high thro which the steam pipe & condensing pipe are passed, this is covered with a cylinder of sheet iron leaving a small space i & k of about ⅙ of an inch between the block & the iron cylinder which is to operate as a piston. To this the working rod is to be fixed, this passes thro a stuffing box on the top of the external cylinder (omitted in the drawing)—C is the outward cylinder which may also be made of sheet iron. The intermediate space is to be filled with mercury to the hight of 30 inches if not more then a 16 inch stroke is required—If, as will generally be the case, a greater stroke, is sought, the depth of the mercury must be proportionably greater, 63 inches will admit of a four foot stroke, because 15 inches will be transferred from one side of the cylinder to the other by the pressure of the steam.

It is evident that if the steam is let into the inner cylinder or rather, middle cylinder or piston, thro the steam cock G & It is condensed by the condensing pipe H. while steam is admitted above, or between the piston & outward cylinder, that the piston must descend with the whole pressure of the steam, when on the other hand it is condensed without or above & admitted below the piston, it must rise with equal force. As it rises & falls in a fluid, it will feel little friction, but that of the working rod (& even that may be taken off if considered of moment by the use of mercury applied as above)—& that of the rollers placed at the bottom of the piston to prevent its vacilating. The only loss of power in the engine is that which arises from the action of the steam upon the mercury in the downward stroke but this would be extreamly small in an engine of 30 inches neither this, nor the frictions would amount to more than ½℔upon an inch. If air pumps are used they must be formed as the engine is, so as to work with little friction.

The advantages that this engine has over Docr. Watts are. 1st. the little friction, whereas the most approved engines of 30 inches, as I judge from actual experiment, including that of the air pump exceed ⅓ of the whole power or 5 ℔upon a square inch—2d The impossibility of any part of the steams escaping from one, to the other side of the piston, an evil that the greatest care can hardly prevent in Docr Watts engine, after it has run three days. This operates a very considerable loss of power 3d The saving of the time & trouble expended in repacking the piston which must be very frequently repeated, once in 14 days at least, & must therefore require the constant attendance of an artist. 4th. The freedom from wear, An engine on this construction must last for ages.

Water, or oil, may be used where the object is to raise water from mines instead of mercury since by this means the whole machinery may be of wood & a stroke of 16 feet be obtained or any other required length. I have planed a variety of them, but thinking sufficient to shew the principle I will not trouble you with them—

  • a inner cylinder
  • b working rod
  • d. middle cylinder that serves as a piston
  • e. steam pipe to outward cylinder
  • c outward cylinder
  • f. condensing pipe to outward cylinder
  • g. Steam pipe to inner cylinder
  • H. condensing pipe—
  • i & k spaces between the cylinders Alled with mercury to a hight proportioned to the length of the stroke—

MS (DLC); entirely in Livingston’s hand; at head of text: “Cler Mont 5th. July 1800 by Robt. Livingston”; endorsed by TJ as received 31 July.

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