782 HARDENING 



posed of equally long hairs. Tho perfection of tlio pencil depends upon this equality j 

 the tapering point being produced simply by the attenuation of the tips. 



A pinch of one of these parcels is then taken, of a thickness corresponding to the 

 intended size of the pencil ; it is set in a little tin pan, with its tips undermost, and 

 is shaken by striking the pan on the table as before. Tho root end of the hairs being 

 tied by the fisherman's or seaman's knot, with a fine thread, it is taken out of the pan, 

 and then hooped with stronger thread or twine ; the knots being drawn very tight by 

 means of two little sticks. The distance from the tips at which these ligatures are 

 placed is of course relative to the nature of the hair, and the desired length of the 

 pencil. Tho base of the pencil must bo trimmed flat with a pair of scissors. 



Nothing nowremains to bo done but to mount the pencils in quill or tin-plate tubes, 

 as above described. The quills are those of swans, geese, ducks, lapwings, pigeons, 

 or larks, according to the size of the pencil. They are steeped during twenty-four 

 hours in water, to swell and soften them, and to prevent the chance of their splitting 

 when the hair-brush is pressed into them. The brush of hair is introduced by its lips 

 into the large end of the cut quill, having previously drawn them to a point wit h the 

 lips, when it is pushed forwards with a wire of the same diameter, till it comes out at 

 the other and narrower end of the quill. 



The smaller the pencils, the finer ought the hairs to be. In this respect the manu- 

 facture reqiiires much delicacy of tact and experience. 



HAIiIOTIS. The sea ear-shell. A genus of molluscous animals belonging to the 

 class Gasteropoda. These shells, possessing a fine nacre, are extensively used in the 

 ornamentation of papier-mache articles, and mother-of-pearl ornaments. 



HALITE. A mineralogical name for rock-salt. 



HAXil.EFZ.INT A. An old Swedish name still retained for certain felstones. 

 See FELSPATHIC ROCKS. 



HAIiIiQYSZTE. An earthy hydrated silicate of alumina, closely related to clay. 



HAZiOGEN, is a term employed by Berzelius to designate those substances which 

 form compounds of a saline nature by their union with metals ; such are chlorine, 

 iodine, bromine, fluorine, and cyanogen ; the salts thus formed being called haloid 

 salts, from their resemblance to common salt (NaCl), (&Vs, sea salt, and e5f8os, form). 

 Since the discovery of the compound halogen, Cyanogen, some chemists have been led 

 to view all salts as under the type of haloid salts ; assuming in the different acids 

 certain compound halogens, as in sulphuric acid the halogen (SO 4 ), in nitric acid the 

 halogen (NO ), &c. ; which in combination with hydrogen form the acids ; the different 

 salts being formed by the displacement of the hydrogen by the metal, as follows : 

 sulphuric acid (HSO 4 ), sulphate of potash (KSO 4 ) ; nitric acid (HNO 6 ), nitrate of 

 soda (NaNO 6 ), &c. H.K.B. 



HAIiOZBS. Salts formed by combination of a metal with a radical, or halogen. 

 Modern ideas on the constitution of salts have greatly tended to weaken the old dis- 

 tinction between haloid salts and oxysalts. 



HAZ.OTRZCHZTE. A hydrous sulphate of alumina and sesquioxide of iron. 

 See ALUM, FEATHEB. 



HANDSPIKE. A strong wooden bar, used as a lever to move the windlass and 

 capstan in heaving the anchor, or raising any heavy weights aboard ship. Tho handle 

 is round, smooth, and somewhat taper. The other end is squared to fit the holes in 

 the head of the capstan or the barrel of the windlass. 



HANGZNG-WAXiZi. In mining, the upper wall of an inclined vein ; the rock 

 which hangs over the lode. 



HARDENING. The processes by which metals are rendered harder than they 

 are when they first leave the hands of the workman. 



Some metals are hardened by hammering or rolling ; but care is required not to 

 carry this too far, as brittleness may be induced. Sudden cooling is had recourse to 

 with some metals. Pure hammered iron appears after annealing to bo equally soft, 

 whether suddenly or slowly cooled ; some of the impure kinds of malleable iron harden 

 by immersion. Steel, however receives by sudden cooling that extreme degree of 

 hardness combined with tenacity, which places it so incalculably beyond every other 

 material for the manufacture of cutting-tools. 



In hardening and tempering steel there are three things to bo considered, namely, 

 the means of heating the objects to redness, the means of cooling the same, and the 

 means of applying the heat for tempering, or ' letting them down.' 



Steel pens are hardened by being heated in largo quantities in iron trays within a 

 furnace, and then plunged into a oily mixture ; generally they are likewise tempered 

 in oil, or a composition, the boiling-point of which is the same as the t< mprratuiv 

 suited to ' letting them down.' 



Saws and springs are hardened in various compositions of oil, suet, wax, and other 

 ingredients, 'which however lose their hardening property after a few weeks' constant 



