To Matthew Boulton
ALS: Assay Office, Birmingham
London, March 19. 1766
You will I trust excuse my so long omitting to answer your kind Letter per Mr. Garbet,4 when you consider the excessive Hurry and Anxiety I have been engag’d in with our American Affairs. I thank you for introducing me to the Acquaintance of that very sensible worthy Man, tho’ I could have but for a short Hour the Pleasure of his Company.
I know not which of the Valves to give the Preference to, nor whether it is best to introduce your Jet of Cold Water above or below. Experiments will best decide in such Cases.5 I would only repeat to you the Hint I gave of fixing your Grate in such a Manner as to burn all your Smoke. I think a great deal of Fuel will thus be sav’d, for two Reasons. One, that Smoke is Fuel, and is wasted where it escapes uninflam’d. The other, that it forms a sooty Crust on the Bottom of the Boiler, which Crust being not a good Conductor of Heat, and preventing Flame and hot Air coming into immediate Contact with the Vessel, lessens their Effect in giving Heat to the Water. All that is necessary, is, to make the Smoke of fresh Coals pass descending thro’ those that are already thoroughly ignited.6
I sent the Model last Week, with your Papers in it, which I hope got safe to hand.7
Please to make my Compliments acceptable to Mrs. Boulton, and present them likewise to our Friends Mr. and Mrs. Baskerville, and Mr. Small.8 With great Esteem, I am, Dear Sir, Your most obedient humble Servant
To Mr M: Boulton
Endorsed: Benjn: Franklin—19 March 1766.
4. For Boulton’s letter of Feb. 22, 1766, to which this is a reply, and some of the matters discussed here, see above, pp. 166–8.
5. At this point in the margin is a rough sketch of a rabbeted right-angle carpenter’s joint, which appears to have nothing to do with any topic discussed in this letter.
6. At some time between 1771 and 1773 BF completed development of his smoke-consuming stove on the principle indicated here, and he reported in the latter year that he had used it effectively during the previous winter. This letter shows that he had established the theoretical basis of his invention as early as 1766, though he had not yet worked out all the practical details.
7. The model of a steam engine Boulton had asked him to return.
8. John Baskerville, the famous type designer, and his wife, the former Sarah Ruston (above, IX, 257 n), and William Small, a naturalist (above, XI, 480), residents of Birmingham.