| Description | London March 29th 1775
Dear Sir
Yours of yesterday received, I expected better performance from the Engine-The vacuum gage I have always intended but was hindered from applying it because In former expts: I had one & could not get the [mercury ] prevented from jumping into the Cylinder & spoiling every thing; Now that we have an Iron Cylr-I think it may be ventured in the following manner. It must not be applied to the condenser but to the Cylr: by making two branches to the cock that lets the air out of the Cylr: each of wch: must have a cock, one to lett out water and air as usual & the other to communicate with the gage pipe during condensation only, thus [Here follow sketches of the arrangement, in plan and section]. Between the cock & the glass tube must be an Iron pipe with two hollow balls as in the section all sodered with hard solder, these Balls are by way of traps to catch [mercury] in its road to the cock the top of the Glass tube should be contracted [Here is a sketch of the tube] and it should be at least 36 in long
A Brass piston should be tryed consisting of 8 segments standing about 2 inches higher than the fixed ring they should be made of strong plate brass well hamd: and fixed in by the Iron weights, with paper pap the whole should be covered with paper pap about one inch higher than the edge of the Brass. Such a piston should not have in going down by steam above 150lbs of friction & will have very little returning. The power of the engine is 4218lbs
when the steam is 6 inches. The Coln. of [water ] is 3268
The Friction going down is 150
Do coming up 50
To give motion to beam 100
To give motion to [water] 200
Plug frame & condenser 50
Total 3818
remains defective condensation 400 = to 2lbs upon the inch nearly.
My mind runs perpetualy upon condensers with cooling streams your water is too hot at present, however untill I come up the Leaden plugs, & I shall tell you all I have been able to divine about them go on with the . . . engine & get it set to work, A pair of new pumps may be made to the big condenser to take a twelve or 15 inch stroke if we shall find that necessary, for I suspect a logement of Air to be one thing for the condenser does not need to be colder than 100º to come within 1/30 vacuum
Plus valet centies inunctio [mercurii] quam omnes calces ejus diabolicæ; et curatio accelerat; sed magna est Sitis, "A bottle of your Small beer if you please sir" Anoint your piston with Black lead & Hogs lard Adieu
The Rusn: Ambr goes in seven days at furtt:
[The following note was added by Boulton in pencil:] Plus ye decent of Condensing [water] Gage pipe Cok must be shut when ye piston ascends
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