248 



KNOWLEDGE. 



[November 2, 1896. 



simple. Ammonia and carbonic acid are blown througb 

 brine, and bicarbonate of soda, wbich is comparatively 

 insoluble in water, falls to tbe bottom. TVom tliis 

 bicarbonate, soda ash, soda crystals, or caustic soda are 

 made. The weak point about the ammonia process is 

 that all the chlorine, forming more than half the weight 

 of the salt used, is wasted. If it was not for this, the 

 Leblanc process would have bcin defunct long since. 



Until recently all the sulphur of the sulphuric acid used 

 in the Leblanc method was thrown away to form the 

 filthy heaps of tank waste which disfigure tbe country and 

 poison the air in the alkali-making districts, but all this is 

 recovered now by a method described in Knowledge a few 

 years ago. 



By whatever means we accomplish the separation of the 

 chlorine from the sodium in common salt, all that we have 

 to do is to supply the energy necessary to efl'ect the change. 

 Ileat, the attraction of the chemical atoms for one another, 

 and the electrical current are the different forms of energy. 

 In the Leblanc process the first is used ; in the ammonia 

 process the second ; and in the latest method the third form 

 of energy is brought into play. In pumping water up to 

 a reservoir on the top of a hill the work done will be the 

 same whether we employ a steam engine, a windmill, or a 

 hand pump ; but the amount of power expended will 

 depend on the etlicicncy of the pump. A pump with 

 leaky valves that let half the water back again every 

 time the piston is moved would require twice as great an 

 expenditure of energy as a properly constructed machine. 

 It is just the same in manufacturing chemistry. An ideal 

 method on paper may prove very unsatisfactory in 

 practice. Now, the electric current is the ideal way of 

 applying energy for effecting chemical changes, although 

 in practice we have been able to apply it very little at 

 present. When a current of electricity is passed througb 

 a solution of common salt the effect produced on the 

 chemical atoms is exactly similar to the " ladies' chain" 

 in the dance known as the " lancers." All the sodium 

 atoms commence to travel in one direction and all the 

 chlorine atoms in the other, joining hands as they meet. 

 Instead, however, of moving in a circle, as the dancers do 

 in the " ladies' chain," the atoms move towards the two 

 poles or ends of the conductors along which the electrical 

 current reaches and leaves the solution. The chlorine 

 travels towards the positive pole and the sodium to the 

 negative pole. When they reach the poles the atoms are 

 set free, so that from one pole the chlorine gas is given off 

 and from the other sodium, which combines with elements 

 of water to form caustic soda. If this action went on 

 perfectly the electrical process would supplant the others 

 in a very short space of time. Unfortunately, however, 

 the sodium and chlorine atoms have a strong tendency to 

 join hands again after they have been separated ; and 

 although there are other difficulties that are too technical 

 for us to enter into here, nearly the whole of the work 

 done in this field of investigation has been devoted to 

 perfecting a means of preventing the atoms in the 

 electrical dance from becoming partners again. 



The principal contrivances that have been used for this 

 purpose are porous partitions or diaphragms extending 

 across the middle of the cell containing the solution 

 of salt. The amount of ingenuity that has been 

 expended on these diaphragms has been very great, but 

 none of them arc really perfect. The recoQibination of 

 the atoms is never entirely prevented, and, as we might 

 expect, the diaphragm gets in the way of the electric 

 current to some extent, so that a higher power is required 

 to drive the electricity through the solution. The most 

 successful of these processes have been the Greenwood and 



the Le Sueur, which is said to be used extensively in 

 America and on the ('ontinent, where water power is 

 available to drive the dynamos that supply the electric 

 current. In the llargreaves-I3ird process, explained 

 recently in a paper read before the Society of Chemical 

 Industry, the difficulties of having a partition in the middle 

 of the solution have been overcome in a most ingenious 

 way. The brine is placed in the middle compartment of 

 a vessel, divided into three parts by two diaphragms 

 stretching across it. The diaphragms are supported on 

 the outside by copper cloth, which forms the negative pole 

 of the electric current. The two outer compartments, 

 instead of containing brine, are filled with a mixture of 

 carbonic acid and steam. As soon as the current begins 

 to pass, caustic soda is given off at the copper cloth. The 

 soda combines immediately with carbonic acid to form 

 carbonate of soda, which dissolves in the water condensed 

 from the steam and Hows to the bottom of the partition, 

 where it is drawn oft'. The chlorine gas passes off in the 

 meanwhile through an opening in the top of the partition 

 containing the brine, so that the partners, when once 

 they have left the electrical dance, never come near 

 one another again. By this process it is claimed that 

 pure alkali and the strongest bleaching powder can be 

 made at less than five-sixths the cost of the best of the 

 older processes. 



Besides the methods in which a diaphragm is used, 

 other ways have been invented for removing the atoms 

 from theneighbourhood of one another. In two of these, 

 mercury forms the negative pole, towards which the sodium 

 atoms travel. Instead of combining with the elements of 

 water to form caustic soda, the sodium unites with the 

 mercury. This quicksilver is kept in rapid circulation, so 

 that as soon as the amalgam of mercury and sodium ia 

 formed it is removed from the vessel where the action is 

 going on. The amalgam is treated in a separate vessel to 

 recover the sodium in the metallic state, or it is run into 

 water, where caustic soda is formed and the mercury is 

 set free. One of these processes is known as the Castner- 

 Kellner process, and the other has been devised by Mr. 

 Claude Vauiin. The last-named inventor is responsible 

 for another ingenious method, in which fused salt is used 

 instead of brine. The action goes on in a crucible kept 

 hot by the electric current itself. The negative pole in 

 this case is formed of a layer of molten lead at the 

 bottom of the crucible. The sodium amalgamates with 

 the lead in the sann way as it does with the mercury in 

 the process just described. In all the different methods 

 the positive pole or electrode is formed of a rod or plate 

 of gas carbon. 



The non-technical reader may be inclined to regard this 

 account of electrical alkali-making as somewhat dry, and 

 of no particular interest to himself. It is really astonishing, 

 however, to think of the vast revolution the introduction 

 of electrical energy will effect in our industrial life. The 

 whole conditions of life in the country will be changed. 

 Water power will replace coal as the prime source of 

 energy. The cohorts of factory chimneys, belching forth 

 black smoke, which wanders over the sky in ever-in- 

 creasing folds, like some evil genius just arisen from the 

 bottomless pit to shut out the light of day from the 

 workers, will disappear in a great measure. We are 

 not blessed in this country with large rivers, but the 

 water power of the tides running to waste round our coasts 

 is enormous. The power of the tides running past Bristol 

 is sufficient to drive all the alkali works in the kingdom 

 half a dozen times over. The task of providing this water 

 power might well be undertaken by our great maritime 

 municipalities or county councils. All that is required ia 



