MERCIA 



MERCURY 



139 



90,000, and in 1873-74 erected, at a cost of 

 30,000, tlieir present school-house on the site of 

 the old gown boys' quarters of the Charterhouse. 

 Richard Mulcaster \v;is the first master of the 

 school, and among its scholars have been Edmund 

 Spenser, Bishop Andrewes, James Shirley, Arch- 

 bishop Juxon, Titus Gates, Lord Clive, Charles 

 Mathews, and Sir Henry Ellis. See the Rev. C. 

 J. Robinson's Register of the Scholars admitted to 

 M'-ri-hant Taylors', 1562-1874 (2 vols. 1882-83). 



Mercia, the great Anglian kingdom of central 

 England. The name, originally limited to the dis- 

 t rict around Tamworth and Lichfield and the Upper 

 Trent valley, refers to a ' march ' or frontier that 

 had to be defended against hostile Welshmen. 

 The first settlements were most probably made 

 in the second half of the 6th century, but Mercia 

 first rose into real importance, and indeed grew 

 into Middle England, under the vigorous rule of 

 Penda( 626-855). His nephew, Wulfhere (659-675), 

 pushed back the Northumbrians, and extended 

 the boundary southward to the Thames, and Ethel- 

 bald (716-755) spread his conquests round all the 

 neighbouring states. But the mightiest kings of 

 Mercia were Ofla (757-795) ami Cenwnlf (796-819), 

 and after tlieir time its power rapidly declined 

 before the invasions of the Danes on the one side, 

 and the spread of the West Saxon kingdom on the 

 other. At length it became one of the great 

 earldoms, and Elfgar, Leofric, Edwin, and Morcar 

 retained at least the shallow of past power. See 

 E N < 1 L A N D ( History ) ; also 1)1 ALECT. 



Mercury. See HKRMES, PLANETS. 

 Mercury, or QUICKSILVER (sym. Hg; atomic 



weight = 200; sp. gr. I3'6), one of the go-culled 

 noble metals, remarkable as lieiiig the only metal 

 that is tluiil at ordinary temperatures. It is of a 

 silvery white colour, with a striking metallic lustre. 

 When pure it runs in small spherical drops over 

 smooth surfaces ; but when not perfectly pure the 

 drops assume an elongated or tailed form, and often 

 leave a gray stain on the surface of glass or porce- 

 lain. Moreover, the pure metal, when shaken with 

 air, presents no change upon its surface: while if 

 impure it becomes covered with a gray film. It is 

 si j^lilty volatile at ordinary temperatures, and at 

 liiy F. it lioils, and forms a colourless vapour of 

 cp. gr. 6"976. Hence it is capable of being dis- 

 tilled ; and the fact of its lieing somewhat volatile 

 at ordinary temperatures helps to explain its per- 

 nicious effects upon those whose trades require 

 them to come much in contact with it as, for 

 example, the makers of barometers, looking-glasses, 

 >Vr. At a temperature of - 39 F. it freezes, when it 

 contract* considerably, and Incomes malleable. In 

 consequence of the uniform rate at which it expands 

 when heuted, from considerably below to above 

 SIX)', it is employed in the construction of the mer- 

 curial thermometer. 



All mercurial compounds are either volatilised or 

 decomposed by heat; and when heated with car- 

 Inmate of soda they y iehl metallic mercury. Native 

 or virgin quicksilver only occurs in small quantity, 

 illy in cavities of "mercurial ores. Of these 

 ores by far the most important is Cinnabar (q.v.). 

 There are two means of obtaining the metal from 

 the cinnabar : the ore may be burned in a furnace, 

 in which case the sulphur is given off as sulphurous 

 acid, and the mercury is collected in a condensing 

 chamber ; or the ore may be distilled with some 

 substance capable of combining with the sulphur 

 as, for example, with slaked lime or iron filings. 

 The mercury as imported is usually almost chemi- 

 cally pure. If the presence of other metals is sus- 

 pected, it may be pressed through leather, redis- 

 tilled, and then digested for a few days in dilute 

 eold nitric acid, which exerts little action on the 



mercury if more oxidisable metals are present ; or 

 better, in a solution of mercuric nitrate, which de- 

 posits mercury and takes up the more oxidisable 

 metals. The mercury, after being washed with 

 water, is chemically pure. 



Mercury is first spoken of by Theophrastus (3d 

 century B.C. ) ; the name hydrart/i/ros ( whence comes 

 the symbol Hg) dates from Dioscorides. Greeks 

 and Phoenicians procured cinnabar from Almadeu 

 in Spain. After the discovery of the New World, 

 the mercury of Peru was famous. California now 

 produces the great bulk of the mercury of com- 

 merce, and most of it comes from the New Almaden 

 mine. The total produce of California was 60,851 

 flasks (of 76J lb. each) in 1881; in 1888 it had 

 sunk to 33,250 flasks (value 1,413,125). 



There are two oxides of mercury, the black sub- 

 oxide, HgjO, and the red oxide, HgO. Both of 

 these lose all their oxygen when heated, and form 

 salts with acids. The black svboxide, although a 

 powerful base, is very unstable when isolated, being 

 readily converted by gentle warmth, or even by 

 mere exposure to light, into red oxide and the 

 metal : Hg,,O = HgO + Hg. The most important 

 of its salts is the nitrate, Hfe(NO.), + 2Aq, from 

 whose watery solution ammonia throws down a 

 black precipitate known in pharmacy as Mercvriiut 

 soliibitis Hahtiemanni, from its discoverer, and con- 

 sisting essentially of the black suboxide with some 

 ammonia and nitric acid, which are apparently in 

 combination. Of the red oxide the most important 

 salts are the nitrate, Hg( N-O 3 ), + 8 Aq ; the sul- 

 phate, HgSOj, which is employed in the manufac- 

 ture of corrosive sublimate ; and the basic sulphate, 

 HgSO 4 ,2HgO, which is of a yellow colour, and is 

 known as Turjieth Mineral. 



The haloid salts of mercury correspond in their 

 composition to the oxides. Of the most important 

 of these the chlorides there are the subcliloride, 

 HgjCI., well known as Calomel (q.v.), and the 

 chloride, HgCl 2 , or corrosive sublimate. 



The chloride, HgCl 2 , when crystallised from a 

 watery solution occurs in long white glistening 

 prisms ; but when obtained \ry sublimation it 

 occurs in white transparent heavy masses, which 

 have a crystalline fracture, and chink with a 

 peculiar metallic sound against the sides of the 

 Ixittle in which they are contained. This salt 

 melts at 509^ F., and volatilises unchanged at about 

 570". It has an acrid metallic taste. It is sol- 

 uble in sixteen parts of cold, and in less than three 

 parts of boiling water, and dissolves very freely in 

 alcohol and in ether. Corrosive sublimate enters 

 into combination with the alkaline chlorides, form- 

 ing numerous distinct compounds. (A double 

 chloride of ammonium and mercury, represented 

 by the formula CHjNCl.HgCU v Aq, has been long 

 known as sal alttnibruth.) It combines with oxide 

 of mercury in various proportions, forming a class 

 of compounds of great interest in theoretical 

 chemistry, termed oxycltloridcs of mercury. On 

 adding a solution of corrosive sublimate to a solu- 

 tion of ammonia in excess, a compound, which 

 from its physical characters is termed white preci- 

 pitate, is thrown down, the composition of which 

 is HgN 2 H 6 Cl 2 . Chloride of mercury coagulates 

 albumen, and combines with the albuminous 

 tissues generally, forming sparingly soluble com- 

 pounds. Hence, in cases of poisoning with the 

 salt, the white of raw eggs is the best antidote ; 

 and for the same reason corrosive sublimate is a 

 powerful antiseptic, and is employed to preserve 

 anatomical preparations. 



Amongst the most important tests for this sub- 

 stance, which is not unfrequently used as a poison, 

 may be mentioned ( 1 ) iodide of potassium, which, 

 when added to a crystal or to a watery solution of 

 chloride of mercury, gives rise to the formation of 



