Belfast Monthly Magazine

Patent of Mr. John Penwarne of Pancras, near London, for a Method of Giving to Statuesand Other Ornamental Works in Plaister (Gypsum) an Appearance Nearly Resembling theFinest Statuary MarbleSource: The Belfast Monthly Magazine, Vol. 5, No. 24 (Jul. 31, 1810), pp. 55-56Published by: Belfast Monthly MagazineStable URL: http://www.jstor.org/stable/30072648 .

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1810.] Discoveriea and lttprovements in Arts, .Maanufactures, uc. 55

thirds of that used in common fire places for the same effect.

Fire places on this construction are fitted up for public inspection at Messrs. Oddy and Mitchells, Hol- born, corner of Fetter-lane, London.

Obserrations....This fire place pos- sesses advantages which render it wor- thy of public attention. The use of the sand bath in kitchens, has long been thought deseiv.ing of experi- ment by competent judges, and pro- bably would harve been introduced before this, had not the dominion of tho.e lower regionis rested on per- sons rena eakably jealous of interference, and singularly tenacious of old customs with all thmeir rights and appurtenances. It ii probable however that time may soften their rigour in this re- spect, when t-hey perceive how the sand bath preserves the brilliancy of their sauce-pans unimpaired, removes all danger of burning the butter, and saves all that labour of polishing copper and tin, to which they have such a just abhorrence. In short, by the. proper use of the sand bath the business of cookery may be rendered so neat, cleanly, and free from all exposure to inordinate heat, that the most delicate ladies would find nothing to distress their susceptible nervesin performing them, but on the contrary might experience such amusement as would be a considerable resource from the ennui that consumes them, and against which they are at pre- sent otliged to employ so many mi- serable expedients.

On the sand bath, glass and china vessels may be used tor boiling with- out any danger, by which some opera. tions of cookery may be performed with peculiar advantage; baking also may be periormted on the sand bath wito great convenience, by merely placiig the article to be baked on a. dish at,a proper depth, and covering it over close with an earthen vessel. A few trials would soon show the proper way of managing the heat; and the only cautions necessary would be to avoid making prodigious fires, and not to spill greasy liquors on the sand on account of the bad smell which they would ogsation,

Patent of Mr. John Penwarne ef Pancras, ntuar London, fir a AMethod oJ giving to Statues and other Orna- mental

.Wforks in Plazster (Gypsum)

an appearance nearly resembling the finest Statuary Marble, Mr. t'enwarne tius describes his

method of improving gypsum casts. " The principle of my invention is to imprepgnate the plaister cast with alum ; in order to eflict which I pursue (ite

fotlowing process as being the easiest and best adapted for the purpose. A solution of wlum in water is prepared ini a proportion of about one pound of alum to every three pints of water (but is it not

neces. sary to observe the exact propor- tiouis, as a greater. or less quantity of alum will answer the intended purpose). '[lfe liquor is inade to boil sufticientlv to dissolve the quantity of alum 'put into it. The plaister cast, previously dried, and properly finish- ed or cleared offt, is then immersed in this solution, and suftfered to remain therein tronm fifteen minutes to half an hour ; it is then taken out and sus. pended over the vessel containing the solution ; and having been suf. lered to cool for two or three mi- nutes, according to the size and bulk of the figure, some of the so- lution is dipped up and thrown over it, or applied to it by means of a spnnge or linen cloth, and which is continued till the aium forms a fine cr'ystaiization over its surface of a du'e degree of thickness ; then it is sufficiiently dolne it is set by to dry, and when it is periectly so it myv be brought to a degree ofsmoothness, or polish, by means of sand-paper, or glass paper, and finished by beilg rubbed with a fine linen cloth slightly moistened with clean water. As most vessels of metal, except those of tin or lead, are flab!e to impart a stain to the liquor, I make use of wooden vats, which are con- veniently heated by steam introduced through a leaden pipe from a boiler."

Casts managed in this manner possess the beautiful whiteness and transpar- ency of white marble, at the same timne scarcely yielding to it iti hardness, and (for the purposes of interior de- coration) almost equal to it in dura- bility. They are not affectedj by

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56 Discoveries and Improvements in Arts, Manufactures, r4c. [July,

the moisture of the dampest apart- ments ; and 4te even less liable to soil than mat ble, and ate as easily cleaned. By means of this ivenuton exact copies of the works of ancient Lnd mouern sculptois anay be ob- taitied, at a price not much exceeding that of plaister.

On the Muriate of Tin, by Mr. E B3e ard, Ex-projessor oj Chemistry at the Mledzcal School (f c/lompel- tier. Annales de Chemze, v. 68, p.78. 'i he solution of tn by imuratnl acid

as directed by various authors, and as piactlsed b3 Baume, is effected by pourmg on one pait of

tit metal, ji a state of extemne division, four paits of common mut tatic acid, and assiaitng the chemical action by the heat ot a sand bath.

' he water

sesving as a vehicle, to the acid is decomposed ; the oxIgen oxides the metal, which then combines with the acid ; while the hydrogen is evolved in the state of gas, carrying with it some particles of the metal employed, winch tender it very twrtd. But the action a slow, and the dissolution is imperfectl) etiected. ( have obsei red, that a vety large portion of the acid is completely lost by evaporation, and that it you would dissolve the whole of the metal, you must not only add fresh acid, to supply the place of what is thus wasted, but keep up the action by artitcial heat lor set etal days. M. Berard, the author of this paper, tried to effect this operation in the cold, and two months were in-

sdifzuient Bayen and Chailand, in

their experiments on tin, employed as much as six months.

Mi. Chaptal assists the chemical action between mutatic acid and tin, by placing the metal, when lie prepaies the acid, im the jars of Woulfe's apparatus in which is the water to absorb the .vapours. I he neat that is evolved has an excellent

etiect, and the action becomes ve ry btisk towards the end of the process. But this ingemous device leaves some- thing still to be desired, as the acid dissolves only a fouitt of its weight of tin, aind the solution requies to be finished by other means.

The solution of tin is better ef- fected by admitting into a large ie

ceiver, in which theie is a sufficient quantity of the nmetal in a state of

divislGIt, the vapours of muriatic acid

evolved from a mixture of powdeied mrot ate of soda and sulphutic acid diluted to 40Q of the areometer for acids. In proceeding thus by simple distillation, tie vapouts of mniiiatic acid ate jpretty easily condensed anti combined with the tin.

it the vapours of oximuhnatic acid be received Ito a vessel containing tin anoi common

muIltxtic acid, the solution is efected completely, and in a slott t me. 'Ihe acid at 201 will take up a third of its weight of tin

The author tried various mixtures of muitatic and mitric acid, contain- ing flim a sixth to a tenth of the latter. I hey all acted on tln with extreme violence and heat, and the coijtents of the ves&el 'were thrown out with violence, one palt of nimtc acid, or aquafortis of the shops, at 350 of Baume's areometer, and twelve paits of common muriatic acid at 20Q form a mixture well adapted to the solution of tin, which it ettects very well, and min a little time.

'Iflss mixture takes up about a third of its weight of tin, and the solCtion is carried to 450,

Jle author attempted to combine the alteinate action of muriatic acid, and of atmosphe ic air on tin divided into small grains for the puipose of dissolving it, with complete success, With this view he filed a large wide mouthed glass bottle wi th finely granu- lated tin, coveted the

,ntcal will mu tatic acid at 20, left this to act on it for a few hours, and then pouted oft the acid into another vessel ; when it was found to have tisen to 25g. 1hlie tin soon began to giow black fi om the contact of the at. mnosphete, absoltbed oxigen from it and cloii was evolved, rendeting the metal very hot. A lghted candie put into the bottle was quickly extin- guished. As soon as the bottle be- gan to grow cool, the acid was e:- tunned into it, winch acted with flesh force, and in a little tunime got to 359. He pouted it off again, to let, the air act on the tin, and then returned it into the bottle afresh, and thus continued proceeding alternately till

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