162 DUCTILITY 



to establish a state of more easy oxidation in the oils, so that they assume readily the 

 conditions of a resin. 



DRY ROT. This kind of decay in wood is ascribed to the attacks of fungi, 

 especially to Polyporus hybridus and Thelephora putcana. There is no doubt that, 

 by the formation of fungus, rot or decay may be commence 1, and continued to a 

 certain extent ; but there are numerous cases whore rot is due to an entirely different 

 cause a spontaneous decomposition. 



Dry rot differs but little in the causes producing it, or in the result, from WET 

 ROT. They are both alike the effect of the conversion of the carbon of wood into 

 carbonic acid, and its hydrogen into water. The process is again the same as that 

 by which wood is converted into humus, and into brown-coal. Mayer gives the 

 analysis of oak wood, and of humus produced from it, as follows : 



Oak wood. Humus. 



Carbon 52-53 48'32 



Hydrogen . .... 6'27 4-57 



Oxygen 42'20 36'58 



In this change, 773 per cent, of carbonic acid and 2'8 per cent, of carburctted 

 hydrogen are disengaged. 



The examination of the decay of wood, and its conversion into the brown powder 

 (humus) which marks rottenness, shows that the change is almost entirely dependent 

 on the absorption of oxygen. The decrease in the volume of wood during its decay is 

 difficult to account for, unless we suppose, which is probable, that as much escapes in 

 the form of carburetted hydrogen as there does of carbonic acid and water. 



Hollow trees are sometimes met with, whose wood is entirely decayed away, 

 nothing being left but the bark, and a quantity of pulverulent wood, which is altogether 

 disproportionate to the hollow space. In most cases, likewise, the cavity extends so 

 far below the lateral opening in the trunk that wo cannot suppose the decayed wood 

 to have been washed away by rain, at least, not during the last stages of the change. 

 It is, therefore, very desirable that continued careful observations should be made 

 with regard to this point. On the other hand, the slight loss of substance by the 

 wood during the first stages of its decomposition, explains why the alteration of 

 wooden piles under water appears to have taken place without any diminution of 

 volume. If, indeed, besides this, inorganic substances for instance, silica should bo 

 introduced into the place of the organic constituents separated, it would not be 

 difficult to account for the increased firmness and density presented by wood which 

 has remained for some time under water. It has been seen that the conversion of 

 ligneous fibre into a pulverulent substance, and into humus, admits of adequate ex- 

 planation by means of the three cases mentioned above, and, what is especially 

 important, that it may be supposed to take place independently of external oxygen. 

 The formation of carbonic acid is, then, during the first stages of the decomposition, 

 either extremely small or altogether wanting. The change commences with the 

 separation of oxygen and hydrogen in the form of water, and the separation of 

 oxygen and carbon, as carbonic acid, does not commence until a later period. It is, 

 likewise, probable, that at a still later period carbon and hydrogen are separated in 

 the form of carburetted hydrogen. 



The remedy for dry rot is the use of such substances as will, when penetrating the 

 wood, combine with its albuminous matter, and solidify it. Hence corrosive subli- 

 mate, sulphate cf copper, and arsenic acid have been*found to be excellent preserva- 

 tives. Where they can be applied, nitric acid and sulphuric acid are very advan- 

 tageous, especially whore the growth of fungi is the cause of rot, or when vegetation 

 has followed the decomposition, as it not unfrequently docs. See WOOD PRESERVING. 



DUALIZE. A sawdust gunpowder impregnated with nitroglycerine. It re- 

 sembles dynamite in most respects, but is not equal to it. See DYNAMITE ; EXPLO- 

 SIVE COMPOUNDS. 



BUCK. (Duk, a cloth, Swedish ; Tuck, Ger.) A coarse cloth, a light sort of 

 canvas. It is used for common articles of apparel, for small sails, and the like. 



DUCTILITY (StrcckbarJcdt, Gcr.) is the property of being drawn out in length 

 without breaking, possessed in a pre-eminent degree by gold and silver, as also l>y 

 many other metals, by glass in the liquid state, and by many semifluid, resinous, and 

 gummy substances. The spider and the silkworm exhibit the, finest natural exercise 

 of ductility upon the peculiar viscid secretions from which they spin their threads. 

 When a body can bo readily extended in all directions under the hammer, it is si id 

 to be malleable, and when into fillets under the rolling press, it is said to bo laminable. 



There appears to be therefore a real difference between ductility and malleability ; 

 for the metals which draw into the finest wire are not thoso which afford the thinnest 

 leaves under tho hammer or in the rolling press. Of this fact iron affords a good 



