June 7, 1900] 



NATURE 



139 



ivellner, ihe kathode being a layer of mercury at the bottom of 

 the bath. On the current being passed, the potassium liberated 

 at the kathode dissolves in it, forming an amalgam, which as it 

 is formed is drawn off and run into pure water, the water being 

 decomposed, assisted by an auxiliary current, with evolution of 

 hydrogen and formation of caustic potash, which is obtained in 

 the pure condition by evaporation. Carbonate of potash may 

 be prepared by passing a stream of carbonic acid gas into the 

 caustic liquors before evaporation. In commerce, naturally, it 

 is more general to electrolyse the cheaper sodium chloride, at 

 any rate, in this country. Strontium and barium chlorate are 

 also manufactured by electrolysis of their chlorides. 



It has been found possible to prepare painters' colours by 

 electrolysis, e.g " while lead" is obtained in a very pure con- 

 dition by electrolysing a dilute solution of sodium chlorate and 

 carbonate, the electrodes being of lead. If the sodium carbonate 

 is replaced by sodium chromate, a neutral lead chromate is 

 produced, an acid chromate being formed by cautious addition 

 of a solution of chromic acid during the electrolysis. 



To attempt to mention, much less to describe, the enormous 

 number of inorganic compounds and elements which have been 

 prepared or isolated by the aid of electricity, would be, in an 

 article such as this, impossible ; but .sufficient examples have 

 been given to show the importance of electrical processes in this 

 branch of chemistry. 



Turning now to organic chemistry, we notice that, although 

 a vast amount of work has been done, it is more of theoretical 

 interest than of technical value. But now that the initial 

 difficulties have been to a large extent overcome, and the inanner 

 in which the reactions take place is better understood, it is 

 probable that shortly this branch of manufacturing chemiMry 

 will also undergo a revolution in the hand of the electro-chemist. 

 As a means of synthesis and of proving the formula of substances, 

 electrolysis has been, and is, of great value to the organic chemist. 

 Thus on electrolysing a solution of an alkaline acetate, ethane 

 is produced ; whereas by employment of a succinate, ethylene is 

 formed, a solution of fumaric acid yielding acetylene. These 

 are, of course, simple cases ; but even that seemingly unsolvable 

 problem, the constitution of camphoric acid, has been attacked 

 by Walker, and by means of electrolysis of it and its derivatives 

 he has obtained results which must be of great value in ulti- 

 mately deciding what is the correct formula for this substance. 



Iodoform can now be produced in a state of great purity by 

 electrolysing a solution of potassium iodide and sodium carbonate 

 to which alcohol has been added. On electrolysis, employing 

 electrodes of platinum, iodine is continually set Iree at the 

 anode, and coming in contact with the alcohol at the moment 

 of its lil)eration produces iodoform. As the reaction proceeds 

 some of the iodine becomes converted into hydriodic acid, and 

 ' this combines with the alkali liberated at the kathode, or which 

 has been added to the bath, potassium iodide being regenerated, 

 which by the further passage of the current is again split up. 

 The process is a continuous one, the iodoform being from time 

 to time removed and a further quantity of alcohol, potassium 

 iodide and sodium carbonate added. It is interesting to note 

 that the alcohol cannot be replaced by acetone, as in this case 

 only a very small quantity of iodoform is produced. Chloroform 

 and bromoform have not been successfully prepared by this 

 method. Chloral can, however, be produced by electrolysis of 

 a solution of potassium chloride at ioo°, to which alcohol is 

 from time to time added. 



By the electrolysis of nitrobenzene in a strongly acid alcoholic 

 solution, aniline is produced. If the nitrobenzene is suspended 

 in concentrated hydrochloric acid, ortho- and para-chloraniline 

 are formed. By electrolysis under other conditions, azobenzene, 

 hydrazobenzene or azoxybenzene are obtained. 



By the electrolytic oxidation of aniline, dye products can be 

 obtained the nature of which depends upon the solution em- 

 ployed, the .strength of the current and the material of the 

 electrode, e.g. if an aqueous solution of aniline hydrochloride, 

 which may be either acidified with sulphuric acid or be practi- 

 cally neutral, is electrolysed, platinum electrodes being em- 

 ployed, a green precipitate is produced at the anode, which 

 becomes violet, bluish-violet and finally almost black, practically 

 the theoretical quantity of aniline biack having been formed. 

 If the aniline contain toluidine, then mauveaniline, rosaniline, 

 &c., are produced. 



Attempts have been made to obtain alizarine by electrolysis 

 of anthraquinone in strong alkaline solution ; indeed, small 

 quantities are said to have been obtained. 



NO. 1597, VOL. 62] 



It has even been found possible to utilise electricity in the 

 dyeing of cloth. When, e.g. a piece of cloth is soaked in a 

 solution of aniline sulphate and placed between two metal 

 plates, which are connected with opposite ends of a dynamo, 

 and the current passed, the aniline sulphate is converted into 

 aniline black ; indeed, by altering the strength of the solution 

 and the density of the current, shades varying from green to 

 deepest black can be produced. 



In the case of indigo the cloth is thoroughly impregnated 

 with a thin paste of indigo-blue and caustic alkali ; it is then 

 placed between two metal electrodes. On the current being 

 passed, the insoluble indigo-blue is converted by reduction into 

 the soluble indigo-white, which on exposing the cloth to the 

 action of air becomes again oxidised and the material dyed blue. 

 Patterns may be printed on the cloth by cutting or stamping the 

 plates in relief, or by connecting one pole to a metal plate and 

 the other to a metallic pencil, when patterns, «S:c., can be readily 

 sketched upon the material (Goppelsrueder). 



Such processes as have been described in these articles appear, 

 when seen in print, as extremely simple. Theoretically they 

 may be so ; but in practice, the carrying out of these seemingly 

 simple operations is often attended by great difficulties. For 

 example, the temperature must not ht allowed to rise too high 

 or fall too low. The quantity of current and its potential 

 require often to be kept within extremely narrow limits, as the 

 following simple example illustrates. 



Silver and copper can be separated by means of electrolysis, 

 the silver alone being deposited if a very low current density 

 (•10 ampere) is employed, whereas with a higher density ("50- 

 I'O ampere) the copper is deposited. Naturally, then, if at the 

 commencement of the operation the higher current density is 

 employetl, both metals will be deposited together. Many of 

 the difficulties to be overcome are to a large extent engineering. 

 And it is to a considerable extent due to collaboration of chemis s 

 and engineers that the science of electro-chemistry has become 

 what it is. 



Electro-chemistry is quite in its childhood, but it is making 

 marvellous and rapid progress. Works dealing with technical 

 chemistry but a few years old require to be revised, owing to the 

 alterations which this branch of chemical industry has brought 

 about. 



It is humiliating to realise that in this country there is hardly 

 a book on the subject to be obtained, and in most cases even 

 these are only translations from Continental works. And it is 

 to be feared that unless this branch of chemistry becomes more 

 studied than it has been up to the present, we shall find in the 

 near future that electro-chemistry, both theoretical and practical, 

 is the property of Ainerica and the Continent. 



F. MOLLWO Perkin. 



ROAD LOCOMOTION.^ 

 T^HE author commenced by s.iying that the subject or 

 mechanical propulsion upon cominon roads had now 

 reached a point when it deserves the very careful consideration 

 of mechanical engineers. 



For many years the uses and importance of the traction 

 engine have become more and more reco.^nised, but its work 

 covers only a portion of the field for mechanical propulsion on 

 roads, and he went on to consider what has led to a general 

 revival of a movement for lighter road-locomotives which about 

 seventy years ago, in the days of Hancock and Gurney, reached 

 a point that for a time appeared to be leading to permanent 

 results of the most important kind, but which ended in com- 

 plete failure. In one sense this revival is undoubtedly due to 

 the passing of the Locomotives on Highways Act in 1S96, 

 previous to which, for more than twenty years, a law had 

 existed which made it impo.ssible for any self-propelled vehicle 

 to proceed at a rate of more than four miles an hour. The 

 immediate cause of the passing of this Act was the attention 

 aroused in this country by the successful introduction of the 

 motor vehicle for purposes of pleasure in France. The real 

 causes of the present movement were probably to be traced to the 

 gradual feeling amongst all classes of the community that modes 

 of transport, both for purposes of pleasure and business, on the 

 roads had not kept pace, or indeed had made little progress at 

 all, compared with the great changes which had been effected 



1 .Abstract of a paper read before the Institution of Mechanical Engineers 

 by Pi of. Hele-Shaw, F.R S., April 26. 



