THE POPULAE EDUCATOR. 



are given for proficiency in various subjects, among which 

 classics, mathematics, Hebrew, theology, law, and poetry are 

 included. They are competed for by the best men of all years, 

 and their value to the successful candidate consists as much in 

 the distinction which they confer as in the pecuniary emolument 

 which they bring 



We have thus endeavoured to give our readers some slight 

 sketch of the University and of its internal dealings with its 

 own members. We shall consider in another article the local 

 examinations which it holds, both for youths and young women, 

 in various parts of the country. 



LESSONS IN CHEMISTRY. XX Y. 



METALS PROPER confnucd. 



LEAD continued. 



DRY air has no action on lead ; but if moisture be present, the 

 bright surface of the metal is soon tarnished by a closely-adher- 

 ing film of oxide. Lead, on account of its pliability, is much 

 used for water-pipes and cisterns ; but it should never be used 

 for storing rain-water, for this is pure water containing air, and 

 in such water the oxide of lead is soluble, rendering the liquid 

 poisonous. Well-waters, containing nitrates and chlorides, act 

 on lead, forming soluble salts, therefore they should not be 

 brought in contact with it ; but hard waters have little or no 

 action on the metal, for a thin deposit of sulphate or carbonate 

 is formed on its surface, preserving it from further attack 

 However, water charged with carbonic acid gas is capable of 

 dissolving the lead carbonate to a dangerous extent. 



Lead is used in several alloys : shot is composed of lead, which 

 is alloyed with a little arsenic, to render it hard and more easily 

 granulated. The other important alloys have been mentioned. 

 There are three other oxides of lead. 



Plumbic oxide, or litharye (PbO), is a yellow powder formed 

 when lead is heated in a current of air. It is soluble in caustic, 

 potash, or soda ; and if the solution be allowed to stand, car- 

 bonic acid is gradually absorbed from the air, the alkali rendered 

 a carbonate, and the lead oxide deposited in transparent dode- 

 cahedral crystals. Litharge is capable of fusion, and then com- 

 bines with glass, etc., forming fusible plumbic silicates. It is 

 largely used as a flux, and for glazing earthenware. A solution 

 of it in lime-water is prepared for a hair-dye. The lime par- 

 tially decomposes the hair, when the lead with the sulphur in 

 the air forms lead sulphide, staining the hair black. 



Peroxide of Lead, or Plumbic Dioxide (PbO,), is a brown 

 powder obtained by digesting red-lead in nitric acid. It can 

 be decomposed by a high heat, becoming litharge, and giving 

 off oxygen. With sulphuric acid a sulphate is formed, and 

 oxygen comes off ; with hydrochloric acid chlorine is evolved, 

 and a plumbic chloride is made. 



Minium or Red Lead (PbO,Pb0 2 ) is a compound of the other 

 two oxides ; it is obtained by heating plumbic oxide or massicot, 

 but not sufficiently to fuse it into litharge ; it absorbs oxygen, 

 and becomes bright red. Its chief use is in the manufacture of 

 flint glass ; it is also employed to colour inferior sealing-wax 

 and in paper-staining. At a high temperature it parts with 

 some of its oxygen and becomes litharge. 



Plumbic Carbonate, or Wliite Lead (PbO,C0 2 ), is the well- 

 known paint ; it may be obtained in a state of purity by pre- 

 cipitation from a solution of a plumbic salt by an alkaline car- 

 bonate. To procure it in large quantities, sheets of lead are 

 exposed to the simultaneous action of acetic acid and carbonic 

 acid. This is effected by placing the sheets rolled into coils in 

 earthenware pots, at the bottom of which is some crude vinegar 

 (acetic acid) ; these pots are packed in manure, from the fer- 

 mentation of which the carbonic acid is supplied. The acetic 

 acid, volatilised by the heat of the fermentation, attacks the 

 metal oxidised by the air, forming acetate of lead (sugar of 

 lead). The carbonic acid gradually displaces the acetic acid 

 from its combination, and thus the plumbic carbonate is formed. 

 Lead Sulphide (PbS). Galena has been noticed as the chief 

 ore of lead. Artificially, this compound may be produced by 

 passing a current of sulphuretted hydrogen through a solution 

 of a lead salt. Dilute nitric acid causes this compound to 

 deposit its sulphur ; but if the acid be strong, both the lead and 

 the sulphur are oxidised, forming a lead sulphate. 



Plumbic Chloride (PbCl 2 ) is precipitated from a solution of 

 the nitrate by the addition of sodium chloride. It combines 



with lead oxide in several proportions ; with 7 molecules of tho 

 oxide it forms Turner's yellow ,- with one molecule a white paint 

 is produced, which is prepared by Bell of Newcastle. Cassel's 

 yellow is still more basic. 



Iodide of Lead (PbI 2 ) falls as a beautiful yellow precipitate 

 when an iodide is added to a lead solution. 



The other salts of lead afford nothing of peculiar interest. 

 The oxalate is the most insoluble, and therefore its precipitate 

 offers a good test for the presence of the metal. 



Besides the characteristics of these salts, already mentioned, 

 lead may be reduced with ease on charcoal ; thus its presence is 

 by no means difficult to ascertain. 



The Noble Metals have already been defined to be those which 

 are capable of being reduced from their oxides by heat. They 

 are nine in number : Mercury, silver, platinum, gold, palladium, 

 rhodium, ruthenium, osmium, and iridium. 



MERCURY OR QUICKSILVER. 



SYMBOL, Hg COMBINING WEIGHT, 200 SPECIFIC GRAVITY, 13-59 

 DENSITY OP VAPOUR, 100.* 



Occasionally mercury is found native, disseminated in small 

 globules through the rock. Its chief ore is cinnabar (mercuric 

 sulphide). The extraction of the metal is simple, and is effected 

 either by heating tho ore in retorts, burning off the sulphur, and 

 distilling the mercury ; or by mixing the ore with some body 

 like quicklime, with which the sulphur combines, the metal as 

 before distilling off. 



Cinnabar is mined in many parts of the world : Almaden, in 

 Spain, and Idria, in Carniola, are the most important European 

 mines. 



The metal is imported into England in iron bottles. With most 

 metals it forms amalgams ; but the film of oxide, ever present 

 on the surface of iron, prevents the amalgamation of that metal. 

 At 40 it becomes a solid, crystallising in octahedra ; at 350 

 it boils ; but at all temperatures it seems to give off vapour. 

 In the Torricellian vacuum, the space above the mercurial 

 column in a barometer, globules of mercury may often be found 

 condensed on the tube. 



Hydrochloric acid has no action upon it; with sulphuric acid a 

 sulphate is formed, sulphurous acid coming off. The action with 

 nitric acid is violent, nitrous acid gas being copiously evolved ; 

 when triturated with sulphur or iodine, it will unite with them. 



Its action on the human frame is serious, producing saliva- 

 tion ; and the workmen are subject to " mercurial palsy," a 

 peculiar form of nervous debility. 



Black Mercurous Oxide (Hg 2 O) and the Red Mercuric Oxide 

 (HgO) are tho only oxides. The former is obtained by tho 

 action of potash on mercuric nitrate or on calomel. It is a dark- 

 grey powder, and when heated is decomposed into metallic 

 mercury and 



Red Mercuric Oxide. This oxide may be prepared by heating 

 the metal in the air to a temperature of 300" ; but this process 

 is slow, and the one generally adopted is the decomposition of 

 mercuric nitrate by cautiously heating. In a state of fine sub- 

 division it is yellow ; such is the case when it is precipitated by 

 potash from a solution of the nitrate. 



The sulphides correspond to the oxides. 



Mercurous Sulphide (Hg 2 S) is a black powder, and may be 

 procured by the action of sulphuretted hydrogen, or a mercurous 

 salt. 



Mercuric Sulphide (HgS) is the ore cinnabar, or vermilion. 

 It is prepared artificially by heating together sulphur and 6 

 times its weight of mercury ; the black mass thus formed IB 

 placed in tall earthen pots, the lower parts of which are red- 

 hot. The top is then closed, and after thirty-two hours the vessel 

 is opened ; the sublimation being complete, the vermilion is 

 found deposited on the upper parts of the vessel. 



Mercurous Chloride, or Calomel (Hg 2 Cl 2 ), is usually prepared by 

 triturating 17 parts of corrosive sublimate, moistened with 13 

 parts of mercury, and then subliming. It is a white powder 

 decomposed by the alkalies, but insoluble in water. It is 

 largely used in medicine. 



Mercuric Chloride, or Corrosive Sublimate (HgCl 2 ), is formed 

 when mercury burns in chlorine, or when mercuric oxide is dis- 

 solved hi hydrochloric acid ; it is usually prepared by subliming a 



The density of its vapour is 100, being an exception to the rule. 



