XI NO. 



7. 1 NT. 



with exoew of sulphuretted hydrogen, again altering, and precipitating 

 the boiled filtrate with carbonate of soda. The washed and ignited 

 oarbunate must then be distilled in a porcelain retort with charcoal 

 from lump sugar. 



X.iuc U a bluish-white crystalline and hard metal, brittle at 400 

 I'.ilir. malleable and ductile between 300* and 200, but again some- 

 what brittle at ordinary temperature* 1 . It molts at 773*, and boils at 

 a bright red beat estimated by Deville at 1904. In contact with air 

 the vapour burns with a magnificent greenish-blue flame, forming 

 copiou* white flocculi of protoxide. At ordinary temperatures zinc 

 gradually oxidises in a moist atmosphere, but the superficial film of 

 oxide preserves the remaining metal for a long time unchanged. It 

 readily dissolves in dilute mineral acids, mid in concentrated solutions 

 of potash and soda. It also combines v.iih chlorine, iodino, and 

 bromine at ordinary temperatures. The equivalent of zinc is 327, 

 and its specific gravity 6*8 to 7'1. 



The following are the principal compounds of zinc : 

 Oxide ur Protoxide of /.inc (XnO), Zinr-ichile. This is the oxide 

 which exists in the native carbonate. It may be prepared in various 

 modes : first, by merely igniting the metal in contact with air; in this 

 rase combustion takes place readily, and a light white compound is 

 formed, which was called l>y the old chemists by the various names 

 of niftil albttm, lanajiltildsopliica, p<tmptoli.c, find jtowci'g of zinc. 



Oxide of zinc may also be procured by dissolving the metal in a 

 dilute acid, either the sulphuric, nitric, or hydrochloric, and decom- 

 posing the solution by a carbonated fixed alkali ; carbonate of ' zinc is 

 first precipitated, but this, when heated, loses its carbonic acid, and 

 the oxide is obtained as a yellowish powder. 



In the manufacture of brass an impure oxide of zinc condenses in 

 the flues of the furnaces and is sold under the name of tulty. 



The properties of oxide of zinc ore, that it is inodorous, insipid, 

 insoluble in water, and infusible by heat; it combines readily with 

 acids, and also with the alkalies ammonia, potash, and soda. So that 

 when it is precipitated by them, they redissolve it if added in excess. 

 It U the basis of all the oxisalts of zinc. 



Peroxide of Zinc, probably a binoxide (ZnO, ?), is obtained by taking 

 gelatinous hydrate of zinc, and pouring upon it an aqueous solution of 

 binoxide of hydrogen (oxygenated water), containing about eight times 

 its volume <.{ oxygen gas, and shaking the mixture thoroughly ; the 

 peroxide of zinc resulting from this operation is white, inodorous, 

 insipid, and decomposes spontaneously when kept moist or when 

 heated. It is also decomposed by acids, which dissolve protoxide of 

 zinc and reproduce binoxide of hydrogen. 



Cliliiridc of Zinc (ZnCl) may be formed by the direct action and 

 combination of these elements. When zinc filings are thrown into 

 chlorine gas, heat and light are evolved, owing to their combination ; 

 it is more readily prepared by dissolving oxide, or still better metallic 

 zinc, in hydrochloric acid, and evaporating to dry ness; or by heating 

 the metal in ft tube through which dry hydrochloric acid gas is 

 transmitted. 



The properties of chloride of zinc are, that it is colourless, has a 

 very styptic taste, is readily soluble in water, and crystallises from it 

 with difficulty; it is very volatile at a reel heat. It was formerly 

 called butter of zinc. 



Uromidc of Zinc (ZnBr) is formed by passing bromine in vapour 

 over zinc heated to redness ; or it may be obtained in solution by 

 agitating a mixture of these elements and water : the solution is 

 colourless, and when evaporated till a pellicle is formed, it becomes a 

 crystalline mass on cooling. 



This bromide has a sweetish, astringent taste, and is very deli- 

 quescent ; it becomes dry when heated, and fuses at a red heat. 



Iodide of Ziuc (Znl) is readily obtained by heating iodine and zinc 

 together in water ; the solution, when perfect, is colourless, and is to 

 be evajmrated in a retort, and when the water is entirely separated, 

 the iodide of zinc fuses and volatilises in fine prismatic crystals, liy 

 exposure to the air this iodide it decomposed, the metnl being oxidised, 

 and the iodine set free. 



Sulphide of Zinc (ZnS). This compound, which exists plentifully in 

 nature, is obtained artificially with considerable difficulty, and by the 

 direct action of its elements is perhaps scarcely possible ; but when 

 oxide of zinc is heated with sulphur in excess, a yellow brown 

 sulphuret of the metal is obtained ; when also sulphuret of potassium 

 is added to a solution of a salt of zinc, a white hydrate of the sulphide 

 of zinc is precipitated. 



PhotfJiide of Zinc is procured by strongly heating in a retort a 

 mixture of six parts of oxide of zinc, six parts of phosphoric acid, and 

 one part of powdered charcoal ; a sublimed mass is obtained, which is 

 of a silvery-white colour, metallic lustre, and vitreous fracture. Its 

 composition has not been determined. 



Selenide of Zinc. If the va|x>ur of selenium be passed over zinc 

 heated to redness, the man takes fire and explodes, and the exterior 

 of the vessel is covered with a lemon-yellow powdery substance, which 

 is ielenide of zinc ; this is partially soluble in nitric acid with the 

 evolution of nitric oxide; and a red powder is deposited, which U 

 however finally dissolved. 



We (hall now briefly describe some of the oxisalts of zinc, 01 t'..u*e 

 consisting of acids combined with oxide of zinc. 



Nitrate of /.u.r i/nnXOj I OHO;. This salt is readily obtained by 



the action of the acid upon the oxide of the metal, or upon the meta'. 

 itself ; in the hitter case nitric or nitrous oxide U produced according 

 to the degree of concentration of the acid. 



The solution of nitrate of zinc U colourless, and by due evaporation 

 it jields colourless crystals, which are deliquescent; very soluble in 

 water and in alcohol : they are decomposed by ignited charcoal, and 

 impart to it a greenish-blue flame. 



Hullihntr ,,f /.in,: (ZnOSO s + 7HO). This, which is the salt of zinc 

 most extensively employed both in medicine and the arts, may be 

 prepared by dissolving the oxide of the metal in dilute sulphuric acid ; 

 but it is always procured by acting on the metal it-elf, which i- 

 oxidised by the decomposition of water, with the oxygen of hi Ji it 

 combines and evolves the hydrogen. The solution is colonrle > 

 by evaporation readily yields crystals, which are usually small, ami tin- 

 primary form of which is a right rhombic prism. Sulphate of zinc 

 has a disagreeable metallic taste ; it is not altered by exposure to the 

 air, but if moderately heated loses its water of crystallisation, and 

 when subjected to a high temperature is entirely decomposed, the acid 

 being expelled, the oxide only remaining. This salt is very soluble in 

 water at 60, and much more so in boiling water. There is an impure 

 sulphate of zinc used in the arts, under the name of vhite ritrinl ; it is 

 a colourless granular mass, obtained by the oxidisement of the native 

 sulphide of zinc or blende. 



Carbonate of Zinc (2 ZuOCO, + 3ZnO HO). Metallic zinc and 

 hydrated oxide of zinc are both dissolved by an aqueous solution of 

 carbonic acid ; but the nature of the carbonate formed, when the 

 excess of carbonic acid is expelled by spontaneous evaporation, has not 

 been ascertained. When an alkaline carbonate is added to a solution 

 of a salt of zinc, a white precipitate is obtained, which is the above 

 compound of carbonate and hydrate of zinc, and not a simple 

 carbonate. 



Acetate of Zinc (ZnOC,H 3 0,+ 3HO) is prepared by dissolving either 

 the metal or its oxide in the acid, or by decomposing sulphate of zine 

 by acetate of lead. The solution is colourless, and yields thin rhombic 

 plates, which are not deliquescent, but are very soluble in water. It ia 

 occasionally employed in medicine. 



Characters of the Salts of Zinc. They are usually soluble in water, 

 colourless, have an unpleasant metallic taste ; the alkalies ammonia, 

 potash, and soda decompose them, precipitating a colourless hydrate, 

 which is soluble in excess of these precipitant*. The alkaline car- 

 bonates also decompose the salts of zinc, but the carbonate of ammonia 

 only, when added in excess, redissolves the carbonate thrown down in 

 any notable quantity. Hydrosulphuric acid decomposes neutral, hut- 

 not acid or alkaline solutions of zinc; the precipitate obtained is a 

 hydrated sulphide of zinc. Tincture of galls gives no precipitate, and 

 ferrocyanide of potassium a white one with the salts of zinc. 



Alloys of Zinc. Potassium and sodium form with zinc brittle alloys, 

 decomposable by exposure to air and moisture. With copper it com- 

 bines to form brass, and with iron it yields a very hard alloy, which is 

 very energetically acted upon by sulphuric acid. If plates of hot ir.ni 

 be dipped into melted zinc, they acquire the appearance of tin-plate, 

 and the iron is prevented from rusting. Such coated iron is termed 

 galvanised iron. 



Sheet-zinc is now largely employed for covering buildings. Plates 

 of this metal are also used in the construction of voltaic batteries. 



ZIXC, Midical Properties of. In the purely metallic state, zinc pro- 

 duces no effect on the human system, but its combination with oxygen, 

 forming oxide or flowers of zinc, is sufficient to invest, it with consider- 

 able power over various organs, both those with which it comes into 

 direct contact and some remote ones, especially the nervous centres. Its 

 local action is that of an irritant, astringent, and desiccative, while its 

 remote action is that of a tonic and antispasmodic. The emetic pro- 

 perties of the oxide are less than those of the sulphate or acetate, unless 

 it meets with acids in the stomach. In this way it is rarely employed. 

 It is for its remote effects that oxide of zinc is valued. While it has 

 the properties common to all the metallic antispasmodics, it is dis- 

 tinguished by its power of restraining inordinate action of the nervous 

 system; being calming and soothing. The brain and the function 

 of sensation appear to feel lees of its influence than the spinal cord. 

 Hence the nerves of motion, and the functions of the circulation and 

 respiration, are chiefly acted upon ; it produces its effects speedily, but 

 they quickly disappear when given in such doses as can be safely 

 administered. The long-con tinned use of it seems to produce a dryne&s 

 and induration of the frame, which, if carried to excess, is dangerous, 

 but the lesser degree of which is in all probability the source of the 

 utility of this medicine, by diminishing the mobility of the system ; 

 irregularities in the circulation, and sudden congestions of blood, being 

 the immediate causes of attacks of epilepsy and hysteria, the diseases 

 which are most benefited by oxide of zinc. This desiccating property 

 renders it the most potent means yet discovered of checking the col- 

 liquative perspirations of consumptive persons. (See ' Clinical Lectures 

 on Pulmonary Consumption,' by Theophilus Thompson, M.D., p. 194.) 

 For use in this way, and even for use as an ointment, it requires to be 

 prepared in a state of far greater purity than it is met with when pre- 

 pared for use in the arts. Above all, it must be free from admixture 

 with sulphate of zinc. 



In spasmodic affections of the chest, such as asthma, angina pectoris, 

 and palpitation of the chest, when these do not proceed from organic 





