thmposition forming a Sulslilutefor Portland Stone. 273 



Ex. 2. If the equation of the solid be (Jx* = (a;» + 

 y^+z')\ the density may be = f (x^ r + «'), and the 



XLIV. On a Composition forming a Substitute for Portland 

 Stone. By Mr. Charles W"ilson- of the Borouah of 

 Soutliwark*. ^ -' 



Siu,— -1 BEG leave to lay before the Society instituted for 

 the Encouragement of Arts, &c. a substitute for Portland- 

 stone chnniiey-pieces, made by me, and no other person, 

 at present, in this kingdom, and with such certificates of 

 their utility as I trust will prove satisfactory. 

 I am most respectfully, sir, 



Your very obedient servant, 



No. r>5, Worcester-Street, Queen-Street, Chart FS Wrr soisi 



Borough ofSouthwark, Jan. 28, 1812. CHARLES WILSON. 



^0 C. Taylor, M.D. Sec. 



iVir. Wilson's Process for Art if ciat Stone Ckirnney Pieces, 



_ Take two bushels of sharp drift sand, and one bushel of 

 sifted slacked quicklime, mix them up together with as 

 little water as possible, and beat them well up together for 

 half an hour, every morning for three or four successive 

 day?, but never wet them again after their first mixture. 



To two gallons of water, contained in a proper vessel, 

 add one pint of single size, made warm ; a quarter of a 

 pound of alum, in powder, is then to be dissolved in warm 

 water, and mixed with the above liquor. 



Take about a shovel full of the first composition, make 

 a hole in the middle of it, and put therein three quarters of 

 a pint of the mixture of alum and size, to which add three 

 or four pounds of coarse plaster of Paris; the whole is to 

 be well beaten aud mixed together rather stiff'; put this 

 mixture into the wooden moulds of your intended chimney- 

 J)iece, the sides, ends and tops of which moulds are made 

 of moveable pieces, previously oiled with the following 

 mixture. * 



Take one pint of the droppings of sweet oil, which costa 



• Fronri Trrimacliotn of the Society fur the EncouragemaU of Arts, Manw 



faclures, aiid Commerce, for 1812. The Society voted twentv-five guineai 



to Mr. Charles Wilion for this comniimication, and a model of such a 

 chimney-piece is preserved in the Society'* Rcpositdry. 



Vol.41. No. 180. y//>n7 1813.' S about 



