■86 Canceling the Figure tf a Bolltr for Steam-engines. 



9. The author affirms, that by the affiftance of phofphorus he has decompofed and fepa- 

 rated ths fulphuric, muriatic, and nitrous acids, fronn their bafes ; and that he has tranfmuted 

 the earths by means of phofphoric acid, fo as to obtain confiderable quantities of magnefia 

 from calcareous earth. And he declares, that by bis operations upon phofphorus he has ob- 

 tained procefles, by means of which he has efFcCted the frit of rubies *, the fufion of 

 emeralds, and vitrification of mercury. 



I 



IX. 



Letter of Enquiry reffcHing the proper Form of a Boiler for Sttam Engines, 



To Ms. NiCUOLSON. 



Sir, v-^ 17th April, 1799. 



AM about to erefl; a large fteam-«ng!ne, but am in doubt of the proper conftruition of 

 boilers. Thofe which I ufe at prefent, appear to me very improper for raifing the greateft 

 quantity of fleam with the leaft fuel. The form, however, has been in repute for 10 or 15 

 years paft. My boilers are 8 or 9 feet in height, 4 to 5 in breadth, and 9 feet in lengths 

 Through the middle lengthways is a flue of iron plates, as is the reft of the boiler, and the 

 water muft always cover this flue, confequently ftand 5 to 6 feet deep in the boiler. This flue, 

 with the flues on the outfide of the boiler running parallel to it, is faid to accelerate greatly 

 the producSion of fteam, and to have the fame effedt as a great fire-place below a broad 

 and fhallow boiler. But I have often obferved, that a flame pafling through any flue ia 

 which there are no obflrudions, to make the flame reverberate, communicates very little heat 

 to the fide in proportion to the fuel wafled. And, in my boilers, while the four fides of the 

 internal flue have been perfedlly entire, the end of the flue where it turns ofF has been burnt 

 through. If this internal flue communicates therefore little heat to the furrounding v/ater, 

 the greateft part of the fteam raifed, muft be from the loweft ftratum of water in contact 

 with the bottom of the boiler ; but by the conftruflion this ftratum has to overcome a column 

 of 5 or 6 feet of water. Hence I conclude, that the conftruflion of boilers to raife the 

 greateft quantity of fteam with the leaft fuel fhould be fliallow, and flues placed below, 

 with obftrudions to force the flame againft the bottom. Engineers objefl: to fuch a form 

 on account of the danger of burning the boiler, by inattention in the engine-keeper, in 

 not fupplying water enough always to cover the parts a£ted on by the fire, and the difficulty 

 of preferving a highly elaftic fteam. But furely it is eafy to proportion the fupply of 

 water to the evaporation, and a contrivance fimilar to a ball-cock in water-cifterns would 

 obviate the firft objedfion. By forming the crown of the boiler with a flat arch not 

 far removed from the furface of the water, I can difcover no reafon why fteam as elaftic 

 as in the prefent form of boilers may not be always at command. 



You will oblige many of your readers by giving your opinion on this fubjeft, fo interefling 

 to the arts. 



I am, &c. 



A. MINER. W. 



• // ophe la frite des rubis. An exprelllon wkich I do not underftand. — N. 



The 



