LBAD ZINC. ] 



CHEMISTRY. 



379 



the exceedingly soft nature of the water, owing to its 

 freedom from salts, would induce the solution of the 

 lead in the cisterns and pipes of the city. Whilst we 

 fully admit the prudence and good feeling of those who 

 raised the objections, we are equally glad to find that the 

 denizens of that city still nourish, and that the purity of 

 the water-supply has not been attended by any un- 

 toward danger. Numerous instances, however, have 

 occurred in which serious injury, and even fatal results, 

 have arisen from the water supplied to houses and 

 stables Laving become impregnated with lead ; and there 

 is no doubt that many families have been afflicted by disease 

 arising from this effect, which has not been discovered 

 at the time, but assigned to other sources fo> an origin. 



The combinations of lead are of considerable impor- 

 tance. An oxide is at once produced when lead is 

 heated to the melting point. Its surface gradually 

 becomes coated with a varied-coloured powder, through 

 the oxidation of the metal ; and thus red lead a pig- 

 ment in so much use is produced. The protoxide of 

 lead may be obtained by heating the carbonate of the 

 metal to redness. Massicot and litharge are oxides of 

 lead ; the latter being boiled with linseed oil, pro- 

 duces the drying-oil used by painters. When dilute 

 nitric acid is made to act on the ordinary red lead, a 

 portion only is dissolved, and a nitrate of lead is pro- 

 duced. There, however, remains an insoluble brown 

 powder at the bottom of the vessel, which resists the 

 action of the acid, and is the peroxide. The sulphate of 

 lead may be produced by adding sulphate of soda to the 

 acetate of the metal, both being in solution. It will fall 

 down as a white powder. The game result is obtained 

 by digesting galena (the sulphide) with nitric acid, by 

 which the sulphur is oxidised, and the sulphate, together 

 with some unchanged sulphur, are produced. The chlo- 

 ride is also a white powder, and may be obtained by 

 adding hydrochloric acid to the acetate of the metal 

 The acetate, or sugar of lead, which is employed in 

 medicine, and for other purposes, is a crystalline sub- 

 stance, procured by digesting litharge in vinegar. It has 

 a remarkably sweet taste ; and hence its name. A basic 

 acetate of lead exists, containing less acetic acid, and 

 more base tlian the former. The chromate of lead is pro- 

 duced on adding a solution of chromate of potass to one of 

 acetate of lead, when a yellow powder is precipitated, 

 forming the yellow chrome used by painters. The orange 

 chrome is formed when the yellow is boiled with lime. 



The most important salt of this metal is the carbonate 

 commonly known as wliite lead, and extensively used for 

 painting purposes. It is easily obtained by mixing solu- 

 tions of carbonate of soda with the acetate of lead ; but 

 for commercial purposes, a more economical plan is pur- 

 sued. Thin plates of lead are exposed to the action of 

 the fumes of spent tan, by means of which both acetic 

 and carbonic acids are afforded. Gradually, the external 

 surface becomes coated with a white powder, which is 

 the carbonate. As this is formed, it is scraped off ; and 

 the surface left is again exposed to undergo the same 

 process, until the entire plate is destroyed. It is found 

 in commerce, both in the dry state and ground with oil. 

 This manufacture is peculiarly dangerous to the health 

 of the work-persons ; and females are generally employed, 

 as being less liable to the evil effects than males. Of 

 late years, a compound of zinc has been substituted, to 

 some extent, for white lead in house-painting. 



There are other combinations of lead, such as the 

 iodide, cyanide, <fcc. ; which, however, are of minor im- 

 portance, and are little beyond the range of chemical 

 curiosities. If the tartrate of lead, produced by adding 

 cream of tartar to acetate of lead in solution, be dried 

 and introduced into -a tube, which must then be exposed 

 to a red heat and sealed, a finely divided form of lead 

 will be produced. If the tube be broken, and its con- 

 tents shaken out, they will catch fire, affording what is 

 called pyrophorus. 



ZINC. 

 DUKINO the last few years, the metal zinc has been 



applied to so many useful purposes, as to have superseded 

 lead to a very large extent. It is produced from two 

 kinds of ores, known as calamine and blende ; the former 

 being a carbonate, and the latter a sulphide of the metal. 

 As is usual with most metallic ores, those of zinc are first 

 roasted. By this the oxide is produced ; and the reduc- 

 tion of the metal is efl'ected by heating with pulverised 

 coke. Being volatile, it distils over from the crucible 

 in which it is reduced ; these being placed in a peculiarly 

 constructed furnace. It is afterwards cast into flat 

 plates, and sold in that form as ' ' spelter, " in commerce. 

 If one of these plates be broken, a beautiful crystalline 

 appearance is presented. The facets, however, soon be- 

 come oxidised, and lose their brilliancy. Zinc can be 

 readily rolled out into sheets ; but for that purpose it 

 must be heated to 300 Fah., because both above and 

 below that temperature the metal is brittle, and may 

 even be pulverised. 



Zinc may be drawn into a wire, which, however, has 

 no great amount of tenacity. It is manufactured into 

 nails, and has been extensively employed for coating 

 iron instead of tin. This process is termed, most er- 

 roneously, "galvanising," for no voltaic current has 

 anything to do with the process. The effect of covering 

 iron with zinc is simply that of enclosing a readily oxi- 

 disable metal within one having less attraction for oxygen, 

 and thus of protecting the interior plate from the action 

 of air and moisture. The tenacity of the iron plate is 

 diminished ; and nails over-" galvanised" become so rot- 

 ten as to be easily broken by the fingers, even when they 

 are of considerable substance. Whilst referring to the 

 properties of lead, and its application to domestic pur- 

 poses, we stated that considerable danger exists when it 

 is employed to line water-cisterns for domestic use. Of 

 late, zinc has been advantageously employed for that 

 purpose. Its surface only becomes superficially coated 

 with oxide, which is insoluble in water, in all ordinary 

 cases ; and hence no danger can arise from its use. Zinc 

 is largely employed in the construction of voltaic batteries ; 

 and wag most ingeniously proposed to be attached to the 

 copper sheatliiug of vessels, so as to prevent the cor- 

 rosive action of gea-water on them. The plan failed 

 through a aecondary result taking place ; for shells of 

 molluscs, <tc., attached themselves to the copper, and so 

 impeded the speed of the vessel. 



Zinc, in combination with copper, produces -/rass : it 

 forms alloys with other metals ; aud so its uses have been 

 greatly extended. 



Zinc, like iron, is a very combustible metal ; for in the 

 form of thin shavings it will burn with ease, affording a 

 beautiful blue flame. If zinc be melted in a ladle, and, 

 when red-hot, a portion be cast into the fire, the same 

 result will be produced. A ladle may be filled with melted 

 zinc, and small portions of nitre or chlorate of potass 

 being cast on the surface, a splendid combustion results. 

 A jet of oxygen directed on shavings of zinc which have 

 been previously ignited, affords a beautiful spectacle. 

 The combustion of zinc, as poles of the voltaic battery, 

 produces a blue light fringed with red. 



From the above experiments a white powder is always 

 produced, which is the oxide of the metal. A hydrate 

 of the oxide is obtained by adding a solution of potass 

 to one of sulphate of zinc. The oxide has been exten- 

 sively employed as a substitute for white lead ; and it is 

 to this substance we referred in our remarks on the car- 

 bonate of lead. 



Chloride of zinc is obtained by dissolving the metal in 

 hydrochloric acid. This compound has been recom- 

 mended as an excellent disinfectant ; and its value in 

 this respect has been well tested by the medical boards 

 of health throughout the kingdom. A small quantity of 

 I the solution Is to be sprinkled over any offensive object ; 

 or in applying it in hospitals, <kc. , towels wetted with it 

 may be hung in different parts of the wards or rooms. 

 A remarkable instance of its efficacy came under our 

 notice some years ago (18411). A metal manufacturer in 

 the neighbourhood ot London, employing a large number 

 of hands, was in the habit of using chloride of zinc for 

 soldering purposes ; and considerable quantities of thu 



