Processes in the Useful Arts. 333 



loaded, about four feet water, which difference of two feet and two inches, 

 when immersed will displace a body of water equal to 36 tons weight or 

 more. 



The bilge keels attached to the bottom of the boat, are for the purpose 

 of preventing, in some measure, its flat bottom from coming in too close 

 contact with the mud, when deeply laden, which otherwise might prevent 

 the boat from rising with the flood-tide, when grounded in such situa- 

 tions ; and these bilge keels being firmly united to the bottom of the 

 boat, serve to strengthen the whole of its frame. 



2. Method of condensing wood and giving it a closeness of grain for resist' 

 ing moisture, for the construction of furniture and other purposes. By 

 Mr James Falconer Astlie. 



This useful process, for which the inventor has taken out a patent, con- 

 sists in cutting the timber into planks with parallel surfaces. These planks 

 are passed between parallel iron or steel rollers with highly polished sur- 

 faces, which condense the wood by their pressure. The pressure thus ap- 

 plied must be at first small, and afterwards gradually increased, other- 

 wise the wood will be crushed or split. The best way of applying the 

 principle is to place several pairs of rollers behind each other, the distance 

 between each pair progressively diminishing. The sap or moisture will 

 thus be forced out of the pores of the wood, and the ends and sides of the 

 plank, and it will thus be rendered stronger, heavier, and harder, and 

 less pervious to moisture, than in its natural state. When used in furni- 

 ture, it is less liable to scratch, and does not shrink. Oak and mahogany 

 admit of much more compression than fir or other slight woods, and Hon- 

 duras mahogany may be rendered as hard and heavy as the best Spanish. 

 If one of the rollers is sufficiently bright, a finished polish will be left up- 

 on the surface. This plan is particularly useful in ship carpentry, for 

 making wooden bolts, trenails, and dowels of a compact quality. 



3. Discovery of a Fine Sand for Flint Glass at Alloa, superior to that from 

 Lynn Regis. By Robert Bald, Esq. F. R. S. E. Civil Engineer. 



At a late meeting of the Royal Society of Edinburgh, Mr Bald read an 

 account of a fine sand which he had found at Alloa, and which was superior 

 to the sand of Lynn Regis, so long used both in Scotland and England for 

 the manufacture of flint glass. 



This material occurs among the lower strata of the coal field of Alloa, in 

 the form of a whitish sandstone, which has been long worked for building, 

 and it can be so easily obtained that it may be delivered at Alloa for a shil- 

 ling a ton, whereas the Lynn Regis sand costs 20 shillings in Scotland 

 Upon examining this sandstone, Mr Bald found that it consisted of pure 

 crystals of silex held together with only a slight quantity of matter, from 

 which it could be easily separated by washing, and he immediately recom- 

 mended it as a substitute for the Norfolk sand. A specimen of flint 

 ^lass was accordingly made with it by Mr Marshall of the Alloa Grkw- 

 Wbrks, and we have no hesitation in saying that it is perfectly colourless, 



