10 DECOMPOSITION 



DEADS. Waste on or in a mine. Rubbish. Mine-stuff too poor in ore to pay 

 for working. 



DEAD DIPPING. The process of producing an agreeable pale yellow dead 

 surface on ornamental brass work is so called. The brass work, after the final stamping 

 with its adhering black scale from the annealing oven, is placed in dilute nitric acid, 

 and left in it until the scale may be easily detached ; it is then taken out and washed 

 with water. Again it is plunged in dilute acid somewhat stronger than before, until 

 the surface is covered with minute bubbles, after which it is washed in a solution of 

 argol, and dried in hot sawdust. Dead dipping is also used in the manufacture of 

 the ornamental parts of stoves, especially such as are intended for drawing-rooms. 

 The brass portions of these are treated in the manner described, but the iron or 

 steel after being polished, or ornamented by engraving, is treated with dilute 

 sulphuric acid. 



DEAD OXXt. The oil which is obtained from the fractional distillation of coal- 

 tar, after the light oil or naphtha has passed over. See NAPHTHA. 



DEAD WEIiIiS. Wells which are made to carry off refuse waters. See ABTE- 

 SIAN WELLS, Negative. 



DSADXiY NIGHTSHADE. The Atropa belladonna. It owes its poisonous 

 character to the alkaloid called atropine. See ATROPINE ; BELLADONNA. 

 DEAL -WOOD. See PINES. 



DEBRIS. A term signifying wreck or waste. It has been adopted from the 

 French to express any accumulation of loose materials arising from the waste of rock. 

 It is also applied to drifted accumulations of all kinds. 



DECANTATION. (Eng. and Fr. ; Abgiessen, Ger.) The act of pouring 

 off the clear liquor from any sediment or deposit. It is much employed in the 

 chemical arts, and is frequently effected by means of a siphon, there being less risk 

 of disturbing the precipitate. 



DECARBONISATION. Articles made of cast iron, and, consequently brittle, 

 are decarbonised and rendered tough by being exposed to heat in contact with some 

 peroxide of iron, as the finely-divided hematite ore. Most of the iron articles used in 

 saddlery or harness making are now manufactured by this process. 



DECHENITE. A vanadate of lead, and perhaps also of zinc. It occurs in 

 Rhenish Bavaria, and is named after the German geologist Von Dechen. 



DECIXVIAIi. A tenth part. A Decimal Fraction is one whose denominator is 

 10 or some power of 10. It is not usual, however, to express this denominator, but a 

 period, called a decimal-point, is placed between the unit and the first fractional 

 number. Thus, 1*5 is the same as 1 + T 5 , or one and five-tenths ; in like manner 1*05 

 means one and five-hundredths ; 1'842 signifies one unit and eight-tenths, four- 

 hundredths, and two-thousandths of the unit ; and so on. 



DECIMAL COINAGE is a proposed system in which the unit is divided and subdivided 

 decimally. The coinage of the English florin was a step towards the decimal system ; 

 the value of the florin, or two-shilling piece, being one-tenth of the sovereign. The 

 metrical system of weights and measures is based on the decimal system ; the multipli- 

 cation and division of the unit always proceeding by some power of 10. See METRICAL 

 SYSTEM. 



DECXIiE. A name given by the paper-maker to a thin frame of wood fitting on 

 the shallow mould in which the paper-pulp is placed. 



DECOCTION. The process of boiling a liquid with some organic body, or the 

 liquid compound resulting from the process of boiling. 



DECOMPOSITION. (Eng. and Fr. ; Zersetzung, Ger.) The separation of 

 bodies from each other. The methods employed are almost innumerable, and usually 

 depend on the special reactions of the matters under examination. Wo shall consider 

 a few of the most striking cases in both the grand divisions of the science, viz. 

 inorganic and organic chemistry. In each instance wo shall, for the sake of conve- 

 nience, subdivide into the three classes of acids, alkalis, and neutral bodies. IV 

 however, to this, we must glance at some of the reactions of which chemist- 

 themselves in separating the elements. The decomposition of ordinary metallic salts, 

 with the view of making a qualitative analysis of a more or less complex mixture, is 

 a problem, in general, of extreme simplicity, and directions for the purpose arc to l>r 

 found in all the numerous works on qualitative analysis. The principle on which 

 the modern methods of qualitative analysis are foundeaisthe separation of the metal. i 

 in the first place into large groups by certain reagents, and then, by means of 

 to subdivide into smaller groups, in which the individual metals can bo determint d 

 by special tests. For the sake of simplicity, we shall only consider tho more, commonly 

 occurring metals. The general reagents, by which tho first subdivision is effected, 

 are hydrochloric acid, sulphuretted hydrogen, sulphide of ammonium, carbonate of 

 ammonia mixed with chloride of ammonium, and finally phosphate of soda. Tho 



