BENDING WOOD. 33 



cover the planks with fome fubftance that is a bad conductor 

 of heat, to confine the heat that is difengaged from the fleam 

 within. 



Each boiler having a communication with the interior of the 

 bt)x, by means of a pipe, the fteam is diftributed to each ftage 

 by the tubes bb b, Fig. 3. The vapour arifing from the boil- 

 ing water penetrates the timber with moifture> heats it, in- 

 creafes its elafticity, and renders it fit to be bent. 



Steamers require little care, and little expenfe, but they This procefs Is 

 cannot be ufed for timber of any great thicknefs, fince they no/expenfivc 8 " 

 cannot impart a emperature higher than that of boiling water, but it is not hot 

 and this is not fufficient to give large pieces the degree of pli- *™J J for u & 

 ablenefs neceflary for bending them. 



This lownefs of temperature gave rife to the invention of 3 d - By wetfcnd» 

 the fand-ftove, which is formed of four ftone or brick walls, defcribed. 

 In the middle are two furnaces, with which feveral circular 

 flues communicate, for conveying the heat, the heated air, 

 and the fmoke, to a chimney rifing from each end. On thefe 

 flues are plates of caft iron, which form the bottom of the ca- 

 vity in which the fand is placed ; the flame and fmoke circu- 

 lating in the flues heat thefe plates, and thefe plates heat the 

 fand. This is an imitation of thofe fand-baths which have been 

 long employed in many chemical procefles and in feveral ma- 

 nufactories. 



As the fand may be heated to a temperature above that of 

 boiling water, it can communicate a greater heat to the tim- 

 ber; but were there nothing but fand and timber in the ftove, 

 all the gafefiable fubftances in the limber might be expelled 

 by the heat, and the timber charred. 



To prevent this, one or two boilers filled with water are Steam mu ft be 

 placed in the middle of the ftove. The water converted into ufed wit hthe 

 fteam by boiling penetrates the fand with moifture ; this im- ' 



parts moifture to the timber; and thus the heat that pervades 

 the timber expels from it no more moifture than is replaced by 

 the fand, to that all the proper fubftances of the timber are 

 preferved. 



We will not venture to affirm however, that no portion of and the timber 

 the component parts of the wood is evaporated in this opera- J^yy injured, 

 tion, and that confequently it undergoes no alteration; but 

 with the precaution of taking out the wood to bend it asfoon 

 as it is fufficiently heated and penetrated with moifture, the 

 injury is imperceptible. 



Vol. XII.— -September, 1805, D The 



