ONS IN rilKMISTRY. 



147 



IB mixed with powdered charcoal, and made into a panto with 

 oil or starch ; thu mass is subdivided into pelleta ; these are placed 

 in a tuli.- i.t [ii.n-i-hun, \vhi-h is heated in a charcoal furnace, 

 and a cum at i ohlorino ia passed through it. The aluminum 

 riilnriil" ndeusoa in a cool receiver. The chemical action is 

 \proBsed 



Al.O. + 3C + 6C1 = A1.C1. + 3CO. 



Aluminum Sulpliate (A1,3SO 4 ) is made for the use of the 

 <ly.-r in luru'i' 'iiuuitities in the north of England. Clay, which 

 has been roasted, is acted upon by half its weight of sulphuric 

 :i.-i.!. At \Vhitby, however, this addition of acid in unnecessary. 

 Tin- alum schist contains iron pyrites and in the slow roasting 

 Home of the sulphur of this compound becomes sulphuric acid. 

 Water i* iuMuil, and the clear liquid is drawn off; the iron it 

 i* precipitated as Prussian blue by sodium ferro- 

 On evaporation, tlu'n flexible scales of the salt are 

 obtained. 



Alimis are double salts formed by aluminum sulphates and an 

 alkaline sulphate ; thus common alum is Al a K s 4SO 4 + 24H 2 O, 

 ih:it i*, it is a compound of A1 2 3SO 4 and K 4 SO t (potassium sul- 

 phate) with twenty-four molecules of water of crystallisation, 

 tt is found native in volcanic neighbourhoods, where the sul- 

 phuric acid from the volcano has combined with the potash and 

 alumina in lava to produce it. At the Whitby Alum Works 

 the iron is not precipitated as Prussian blue. In the roasting it 

 becomes green vitriol (sulphate of iron). To the clear liquid, 

 which contains aluminum sulphate and iron sulphate, a solution 

 of potassium chloride is added. The iron sulphate now becomes 

 iron chloride, and the potassium sulphate with the aluminum 

 sulphate form alum. This is separated by crystallisation, and 

 sent to market. 



Soda Alum, or Ammonia Alum, may be made by using the 

 salts of those alkalies, instead of the potassium salt, in the above 

 process. 



The sesquioxides of iron, chrome, and manganese are capable of 

 taking the place of alumina, with its compounds ; hence they are 

 said to be isomorphous with alumina. When they do this in 

 alum, iron alum., chrome alum, or manganese alum is produced. 

 Clay is aluminum silicate, and is the result of the decomposition 

 of felspar, one of the constituents of the primary rocks. When 

 clay is got directly from the felspar, it is called kaolin, or 

 porcelain clay. 



Clay, when it absorbs water, becomes soft and plastic, offering 

 the best of mediums by which the tender rootlets of plants can 

 take up the potash, ammonia, etc., necessary for their growth. 

 The clay used for making bricks must have a largo proportion 

 of silica in its composition. 



The following table will at once show the difference of the 

 various clays : 



Alumina enters into the composition of numerous minerals. 



The zeolites contain their water of crystallisation, and there- 

 fore swell up before the blow-pipe hence their name. Analcime, 

 natrolite, and stilbite are examples of this class. Granite, basalt, 

 garnet, mica, and lazulite ore familiar aluminous minerals. 



GLASS, PORCELAIN, ETC. 



Glass is a compound of silicates of the alkalies and of the 

 alkaline earths ; its properties are too well known to require 

 description. There are various kinds of glasses which have 

 certain distinctive properties duo to their composition which 

 render them valuable for specific purposes. 



Window glass consists of silicates of soda and lime. Soda pro- 

 duces a more fusible glass than potash; and lime, increases its 

 lustre and hardness. One of the best manufactories of plate glass 

 is at St. Gobain, in France, where these ingredients are used : 



300 parti of white mind (iliea), 100 of carbonate of soda, 

 43 of slaked lime, and 300 of eu.Uet, or broken glass, of the 

 same kind. These ingredient* are placed in a conical crucible 

 and melted. The crucible in allowed to stand some time in 

 a high temperature, in order that any impurities may settle 

 to the bottom. The fused glass is then poured oat on a table 

 of cast iron, and the thickness ia regulated by ledge* of the 

 same metal. The liquid glass is made to cover this table 

 rapidly by a heavy roller passing over it. 



As ia the case with nil glass, the plate is next annealed, 

 that is, it is allowed to cool very slowly in an oven whose 

 temperature is gradually diminished during a fortnight. If 

 glass be cooled at all suddenly, it becomes so brittle as to be 

 useless. The grinding and polishing of the plate ia effected by 

 causing one plate of glass to move upon the surface of anoth<: 

 by machinery, the grinding materials being fine sand and water. 

 When a smooth surface is thus obtained, the plate is polished, 

 first by fine emery and then by peroxide of iron. 



Bohemian glass is a silicate of potash and lime, and on account 

 of its infusibility is used in the laboratory. 



Bottle glass, the colour of which is immaterial, is composed of 

 100 parts of sand, 80 of soaper's waste, 80 of gas lime, 5 of 

 clay, and 3 of rock salt. 



Flint glass has these ingredients : Pure sand, 100; red lead ; 

 20 ; pearl-ash, 40 ; nitre, 2 ; and eullet, 100. 



The lead gives great lustre to the glass, by increasing its 

 refractive power ; hence this glass is used for optical purposes. 

 In its manufacture the crucibles are closed, lest the air should 

 "reduce" the lead. It will be frequently observed that thin 

 takes place in a piece of tubing, if held in the blow-pipe 

 flame for some time. It at first appears as if the tube were 

 "smoked." 



Coloured glasses are obtained by the addition of various 

 metallic oxides. Gems are imitated by making a glass which 

 contains as much as 53 per cent, of lead oxide. This is termed 

 " paste." 



Porcelain differs from glass in the great preponderance of sili- 

 cate of alumina in its composition. It consists mainly of clay, 

 which is infusible, and some alkaline silicate which fuses and 

 binds the clay together, rendering it impervious to moisture. The 

 fineness of the ware entirely depends on the purity of the clays, 

 etc., from which it is made. The glaze which covers porcelain is 

 produced by dipping the " biscuit " ware into water in which is 

 suspended finely-ground felspar ; the porous mass absorbs the 

 moisture, leaving the surface covered uniformly with the felspar. 

 It is then exposed in seggars to a very high temperature, by which 

 the felspar is melted and the glaze produced. Stone wore and 

 common "pottery ware" are glazed by means of common salt. 

 The ware is dipped in sand and water, placed in the furnace, 

 into which has been thrown moist salt. The heat quickly con- 

 verts the salt into vapour. In the presence of the steam the silica 

 on the ware decomposes the salt, forming a silicate of sodium 

 which glazes the article, and hydrochloric acid which escapes. 

 The other nine metals of this class having no interest, we pass 



to 



CLASS IV. -METALS PEOPEE. 



ZINC. 



SYMBOL, Zn COMBINING WEIGHT, 65 SPECIFIC GBAVTTT, 7'1 

 MELTING POINT, 423 CENT. 



This metal is never found native, but is associated with 

 sulphur and carbonic acid in its two chief ores, blende and 

 calamine. The former is zinc sulphide, and in England i? 

 usually found with galena, the sulphide of lead, in mountain 

 limestone; the latter is zinc carbonate, of which there are 

 mines in the Mendip Hills. 



Extraction of the Metal from its Ores. The ore, after being 

 crushed, is roasted ; by this process the sulphur of the blende ia 

 burnt away as SO a , and the carbonic acid of the calamine is 

 given off. 



The oxide of zinc which remains is mixed with half its weight of 

 powdered coal, and placed in large clay crucibles ; these are heated 

 in a furnace, their delivery tubes passing through holes in the 

 walls. At first the blue flame of carbonic oxide issues from 

 them, and when this changes to white the metal is distilling. -A 

 long iron pipe, eight feet long, is then fitted on the discharge 

 pipe, and zinc distils into iron vessels placed to receive it at 

 the end of this tube. 



Zinc is a very crystalline metal. A little below 150 it is olt 



