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The Hippopotomus was a piece of agricultural equipment used to raise mud from a river bed. George Washington first learned of this device in a letter sent by Philadelphian Levi Hollingsworth, a merchant who speculated in land in Virginia. Hollingsworth was a member of the agriculture society in Philadelphia, an organization that also included Washington.

Hollingsworth wrote to Washington on August 24, 1785, after learning from "Mr Samuel Jackson of your Neighborhood" about "the desire your Excelency had of raising manure from the mud in the bed of the River Potomack for the purpose of manuring Land." The inventor, Mr. Donaldson, showed Jackson "his new invented Machine for Cleansing our Docks," which, when operated by one horse and three hands, was capable of raising sixty to eighty tons of mud per day.1

Hollingsworth described Donaldson as being "amongst men of the first abilities in point of invention" and attested to the fact that he had seen "his Hippopotomus often at work" and could "assure your Excelency of its great facility in raising mud or Sand from any depth of water." He also told Washington that Donaldson (who he labelled "the Ingenious Inventor") asked him to say that he was willing to send any information or models that might be desired to Mount Vernon.2

In his response to Hollingsworth on September 20, 1785, Washington noted that he had "long been convinced, that the bed of the Potomac before my door, contains an inexhaustable fund of manure; and, if I could adopt an easy, simple, and expeditious method of raising, and taking it to the Land, that it may be converted to useful purposes—Mr. Donaldson's Hippopotamus, far exceeds any thing I had conceived with respect to the first; but wether the manner of its working will answer my purposes or not, is the question." Washington requested some more specific information about the machine.3

Donaldson wrote back directly to Washington on October 1, 1785, answering the request for more information and offered to send a model. Donaldson also sent a description and engraving of the Hippopotomus from the May 1775 edition of the Pennsylvania Magazine: or, American Monthly Museum. Donaldson was thrilled at the thought of having such a prominent client.

George Washington was very interested in the device, thanking Donaldson for sending the illustration and other material, writing on October 16, 1785. Washington stated that he had "a high expectation of its answering very valuable purposes, if the mud, in the beds of our Rivers, is of that fertilizing nature which the appearance indicate; of which I mean to make a full experiment upon a small scale this fall." Washington further explained that "If the quantity of mud which shall be found necessary from this essay to dress land properly, when added to the expense of the Machine for raising it—bringing it to the Land,—cartage, &c &c does not come too high, I should certainly adopt the measure next year, and will then avail myself of the kind offer you have made me."4

Washington experimented that fall with enslaved workers taking mud from the Potomac for use on his fields at River Farm. He continued with those experiments, but there is no evidence of further correspondence with Donaldson.


Mary V. Thompson
Research Historian
George Washington's Mount Vernon



1. "Levi Hollingsworth to George Washington, 24 August 1785," Founders Online, National Archives,

2. Ibid.

3. "George Washington to Levi Hollingsworth, 20 September 1785," Founders Online, National Archives,

4. "George Washington to Arthur Donaldson, 16 October 1785,” Founders Online, National Archives,