1-1.8 



KNOWLEDGE. 



[Jlly 1, 1890, 



.ViH 



i;.,t 



I'riil 



■Sill 



jnj Porioil cf 

 Elevation 



t'lUH't'FltlY.vf 



Marine. Sill 



l"Elev;'ion 



!^5s^Ti!^ 



/.- 



■'rrFiirrst 

 llci 



numbers aud more important in species wlicn compared 

 with that wliicb iuliabitcd the Wiiral when tbo trees of 

 the upper forest bed were llouriehing, or roamed over it 



in later days to 

 ■ atov^n .v.,,,./ tlie present time. 

 It was, however, 

 vastly poorer in 

 species, and these 

 altogether mean- 

 er, when con- 

 sidered beside the 

 grand Ungulates 

 and imposing I'ar- 

 nivora thatanima- 

 ted the district in 

 pre-glacial times, 

 and whose bones 

 have been pre- 

 served in the caves 

 of North Wales. 

 Mr. Morton, who 

 gives a list of the 

 species whose 

 bones have been 

 found in caves 

 sealed up beneath 

 undisturbed beds 

 of boulder clay, 

 enumerates the 

 cave lion, the 

 spotted by ffina, the 

 Arctic bear, the 

 badger, the wild 

 cat, the Irish elk, 

 the reindeer, the 

 wild boar, the 

 woolly rhinoceros, 

 the mammoth, the elephant, and the hippopotamus. On 

 the threshold of one of these caves, and beneath the boulder 

 clay, a tlint flake found purposely fashioned proves that man 

 shared the country, and, no doubt, contested possession of 

 these rock shelters with some of the remarkable fauna which 

 Britain could then boast of, and which has vanished for ever 

 through, among other influences, the increase of population 

 and the revolutionary march of the ploughshare. 



<li!l.' iittlVfJ, 



finiiljicJ-Cla, 



FiQ. 4.- 



'■i 



-Section of the Strata over and undor 

 tlie Forejt Beds. 



ALUMINIUM: ITS HISTORY, MANUFACTURE, 

 AND FUTURE.-II. 



By Samuel Rideal, D.Sc.Lond., F.I.C. 



AT the present time it may be said that all the 

 aluminium brought into the market is the pro- 

 duct of three lactories, viz , the Pittsburgh 

 Reduction Company of Pittsburgh and Niagara, 

 the Aluminium Industrie Actien Gesellschafc of 

 Xeuhaustn on the Rhine, and the Socirte Electrometal- 

 lurgique Fiancaise of Froges in France. The aluminium 

 company which has been at work in England for some 

 years past has found that the chemical process used by 

 them and devised by Mr. Castner cannot compete success- 

 fully with the newer companies, all of which manufacture 

 aluminium by electrolytic processes. Quite recently a now 

 company, under the name of the British Aluminium Com- 

 pany, has been formed in this country with the object of 

 manufacturing the metal by an electrolytic process, and 

 considerable progress has already been made by them. 



These various electrolytic processes differ only very 

 slightly, and depend for their success chiefly on the 



economic production of electrical enerpy. In America the 

 Falls of Niagara, in Switzerland the Schafhausen Rhine 

 Fall, are utilised, whilst the British Aluminium Company 

 have acquired the water rights of the Falls of Foyers in 

 Scotland. Although the cheap production of electrical 

 energy has thus hastened the development of these large 

 industrial undertakings, it must not be for^'otten that 

 about the year 1887 Chas. M. Hall, in America, by his 

 discovery that alumina would dissolve in a molten bath 

 of cryolite and fluorspar, rendered its utilisation in this 

 particular industry feasible. He found that from such a 

 bath a sufliciently strong current of electricity caused all 

 the impurities to separate, and pure aluminium from the 

 dissolved alumina was liberated at the negative electrode. 

 The melted fluorides remain undccomposed if due pre- 

 cautions are observed, so that it becomes possible by 

 feeding the bath with alumina to obtain a continuous 

 separation of aluminium. The electrolysis of the alu- 

 mina is brought about when the electromotive force is 

 equivalent to 2-1 volts, whilst upwards of four volts are 

 I'equired for the decomposition of the fluorides. The 

 composition of the flux is so adjusted by the third patent 

 of Ilall that it has, when molten, a specific gravity which 

 is slightly lower than that of the metal, so that the latter, 

 as soon as it is liberated, falls through the molten mass to 

 the bottom of the electrolytic cell, and is thus prevented 

 from being in contact with the air and so being altered 

 by oxidation. 



The Hall process is the one adopted by the Pittsburgh 

 Reduction Company. In order to obtain the pure alumina 

 for the electrolytic bath, native bcauxite has to undergo a 

 preliminary treatment. This consists in igniting it gently 

 with soda ash, and in this way producing sodium aluminate, 

 which is next treated with sufficient hot water to just 

 dissolve it. Oxides of iron, silica, and other impurities 

 remain undissolved, and the clear decanted solution of the 

 aluminate is then decomposed by carbonic acid gas, obtained 

 by the combustion of coke. The precipitated hydrated 

 alumina is thus obtained pure, and on drying is ready for 

 the bath, whilst the carbonate of soda simultaneously 

 formed is available for a fresh portion of beauxite. The 

 vessels in which the electrolysis is effected consist of iron 

 pots lined with powdered carbon, and are connected with 

 the negative terminal from the dynamo. To the bath of 

 molten fluorides about one- third of their weight of alumina is 

 added. The positive electrodes consist of blocks of compact 

 carbon dipping into the molten mass, and, as already men- 

 tioned, the current use.l is of comparatively low voltage, so 

 as to prevent the decomposition of the fluorides. Each 

 machine produces at Niagara a direct current of two 

 thousand five hundred amperes at one hundred and fifteen 

 volts, and is obtained by transformers from a two thousand 

 five hundred volt alternating current. The amount of 

 energy required to produce one pound of aluminium is 

 about five horse-power hours. The aluminium is liberated 

 in globules which sink to the bottom of each of the iron 

 pots, and there collect into a large molten " button." The 

 first portions, being impure, are removed; the remainder is 

 drawn ofl' at intervals by a syphon, without interruption of 

 the current. Alumina is added from time to time as the 

 decomposition proceeds, so that the process is practically 

 a continuous one. Chloride of calcium is occasionally 

 added to render the bath more mobile and to prevent 

 clogging. During the process the positive carbon electrode 

 is oxidized to carbonic oxide, and has to be renewed from 

 time to time. Theoretically, thirty-six parts by weight of 

 carbon are required to produce fifty-four parts of metallic 

 aluminium — thus : — 



Al, O3 + 3 C = Al.^ + 3 C ; 



