Thomas Jefferson Papers

To Thomas Jefferson from Joseph Leacock, 2[3] November 1792

From Joseph Leacock

Philada. Novr. 25th. [i.e. 23] 1792.


My being at the Pot ash works of Richd. Johns (on business) when Mr. Jefferson came there, to make some Enquiery respecting the manufactury of Pot and pearl-ash, (and, Expressing an intention of beginning the business in the forests of Virginia, where he purposed having the timber Cut down and burnt in the open air,) I considered it my duty to speak a few words on the occasion, having once been Engaged in that undertaking. I informed you sir, that it did not answer the Expected End. I had an Amazing quantity of wood prepared and piled up in large heaps and set fire to, and Expected to have a plentiful harvest of ashes to hale to the works, and was much disappointed. The rapidity of the fire was so excessive as to raise the ashes as they formed, and the wind wafted them away. I am told the Russians burn their wood in Kilns, built under the Knolls of hills, into which the wood is Easily rolled, and, where ‘tis consumed to advantage, but the construction of these kilns, I am unacquainted with, therefore must leave it to be Explained by some person who may have seen it. Probably I may be able to find out such a person, and should you Express a wish of that sort, I will then do it chearfully. With respect to making good Pot and Pearl-ash, be assured it is but a simple thing, in which care is the Essential matter. The Lye must be Clear, or it will not be good after all the trouble, and the Lye ought to be strong, ere it is Evaporated into black salts, in order that less time may be required, and, consequently, less wood, and less Expence. The process of making these salts into Pot ash, is very simple, many artists1 melt them Easily in open kettles, I have been inform’d, but my kittle was always covered with sheet Iron, and I think Richard Johns has improved on it. His fire is so intensely hot as to burn out all the black vegetable oil, which, when left in, is the Cause of the sulphurious smell found in some ill manufactured pot-ash, which is unfit for the bleaching of Linnen. Should Mr. Jefferson incline to make Pearl-ash, it will be necessary to have an ovan for scorching the black salts, as the artist terms it, that is, to burn out the blackness of the salts, with a moderate fire made with dry oak, which is the best of wood for the purpose, and after the scorching is completed, it is then to be put into the kettle with a quantity of water sufficient to imbibe the alkalis2 and set to boil, after which put all the disolved part into a Clean tub to settle for some days, when the white Lyes are to be returned into the kettle, to be Evaporated into white Pearl ash, and carefully stirred, till Evry Lump on breaking, is found to be thoroughly white, and this is the whole art of making Pearl ash in Kettles. This new mode of boiling the scorched salts and putting the solution into the tub to settle, is productive of another good End, i.e. that of leaving all the Neutral-salts, adhering to the side and bottom of the tub, therefore this is pure Pearl-ash, and is of more value (if duely Estimated,) than what has not gone throug this process. Should Mr. Jefferson require further information, I would advise him to apply to Mr. Johns, who is competent to it,3 and makes as good Pot and Pearl-ash, as any I have ever seen. I am sir, your sincere well wisher & huml. servt.

Joseph Leacock

NB. Should any blackness rise on Evavorating the white Lyes in the kettle, care must be taken to skim it off instantly, Ere it settles down again. These black skimings are not to be thrown away, but to be put into tubs among fresh ashes to Extract the alkali.

I can see no reason why those Kilns may not be made on low grounds, in the form of a Cellar walled up, into which the wood may be Easily rolled and burnt, probably it may be necessary to dig a flue below the bottom as an aid hole, to kindle, and keep the fire lively. With respect to Pearl-ash ovans, I must inform you there are several sorts in use. The original ovan, which is a very good one, has two fire places within the arch, one on Each side the door. I need not describe the particular construction of this complete ovan, as their are draughts of it in this City more accurately deleniated than I can describe with my pen. Their is another kind, which I think Equally good, and less trouble in making, and that at Mr. Johns’s is similar to it, but, was I in want of an Ovan for the purpose of scorching the black salts, in order to make them into Pearl-ash in Kettles, as mentioned above, the ovan should be built seperate, from any connection with the kettles. I directed Colonel Anderson of Maryland, to build such an Ovan, haveing the fire behind, to play through a wide, but narrow Apperture over the bottom to the front, with a Chimney to carry the smoke off, just within the door through the Crown of the arch. This ovan has succeeded admirably well he informs me, and says the arch is very low, not more than 14 or 16 Inches high.

Colonel Anderson is daily Expected in this City, and should Mr. Jefferson desire to talk with him on the subject, and will be pleased to intimate it to me, I will inform him. Was my knowledge more Extensive, I would chearfully communicate it.

The burning of Leached ashes with Expectation of gaining more alkali, is but a poor affair. There is in this City a german book, wrote by a Pot-ash maker, in which he gives the result of many Experiments made on such ashes with a view to ascertain wether ‘twas worth the trouble and Expence, and concluded it to be a dirty4 unproffitable business5 and not worth following.

It will be in my power to procure you the perusal of this book, should you desire it sir.

RC (DLC); dateline underneath signature; at foot of recto: “please turn over” (see note 3 below); endorsed by TJ as received 23 Nov. 1792 and so recorded in SJL. Leacock must have misdated the letter, as TJ received it on 23 Nov. 1792 and responded the next day.

1Word interlined.

2Preceding five words interlined.

3After signing and dating the letter, Leacock added the remainder of this sentence, and the paragraph beginning with “NB.,” opposite his signature. He wrote the additions that follow on the verso.

4Preceding two words interlined.

5Word interlined.

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