Kc 



1896.] 



KNOWLEDGE, 



247 



from a beautiful blue to a steel blue, and then we get the 

 second spectrum. 



The first is composed of eighty lines, the second has 

 one hundred and nineteen, and there seem to be twenty- 

 six lines in common. 



The analogy that argon presents with other simple 

 gases lies in the hypothesis that it is itself considered to 

 be a simple body. 



Mr. Ramsay has also been able to detect the presence of 

 argon and also of helium in cleveite, a mineral discovered 

 by Xordenskinld, and found to be formed from oxide of 

 uranium, uranate of lead, and other rare minerals. Except 

 in a meteorite in Augusta County, Virginia, U.S.A., 

 helium had only been observed in the spectrum of the sun. 



M. Bouchard, again, has found that the lines which are 

 characteristic of the spectra of argon and of helium exist 

 in the spectra of the mineral waters of Cauterets. 



51. Deslandres has also observed in cleveite another line 

 which is found in the solar spectrum, and which bids fair 

 to announce to the scientific world the presence of a new 

 element common to the atmospheres of the sun and the 

 earth. 



Lastly, M. Berthelot, in his study of the spectra of 

 fluorescence, has discovered, with argon charged with the 

 vapour of benzine and submitted to moderate magnetic 

 action under certain conditions which appear to correspond 

 to a particular state of equilibrium, that this absorbed 

 vapour does not pass away even after a considerable time 

 has elapsed. First a violet tint is obtained with a sprinkling 

 of fiery red, then a beautiful green fluorescence which is 

 visible in broad daylight even at a distance. The clearest, 

 most characteristic, and most brilliant line is green ; of the 

 rest, almost as brilliant are a yellow line and two violet 

 lines, the latter less visible than the others ; but there is 

 one line, the last of the series, which can only be seen in 

 total darkness. These lines correspond to the brilliant 

 lines of argon considerably rarefied. 



The appearance of the lines due to fluorescence at 

 atmospheric pressure seems to indicate the existence of a 

 combinaiion of hydro-carbonate of argon of the same order 

 as hydrocyanic acid. 



From certain lines coinciding with the lines of the 

 vapour of mercury rarefied, M. Berthelot concludes, that 

 he has produced a complex equilibrium — or, rather, a 

 condensed compound, originating when the mercury and 

 the elements of benzine come between at the same time 

 as the argon. 



♦ 



ALKALI-MAKING BY ELECTRICITY. 



By C. F. TowxsEND, F.C.S. 



THERE is hardly a single industry, from the cottage 

 laundry to the mill where the paper is made on 

 which this article is printed, in which alkali, in 

 some form or other, is not used in large quantities. 

 Under the term " alkali " we include ordinary 

 washing soda, and soda ash, caustic soda, and caustic 

 potash. Until the end of the last century all the alkali 

 used by the world was obtained from vegetable or mineral 

 sources. Of the former, potashes or the ash obtained by 

 burning wood or vegetable matter is still a product of 

 commercial importance, being used in the manufacture of 

 soft-soap. Barilla, which is the ash of a plant that 

 grows plentifully on the salt marshes of Spain and the 

 neighbouring parts of France, was of considerable impor- 

 tance in soap-making and kindred industries f'fty years 

 ago ; but a very small quantity is imported into this country 

 at the present day. Kelp, which is obtained by burning 

 seaweed on the coasts of Scotland and Ireland, con- 



tains a small proportion of soda, but is chiefly valuable 

 as the source of iodine and bromine. As regards 

 mineral sources, soda is obtained from the various 

 deposits of alkali in the more tropical regions of the 

 world. 



It was not until just before the French Revolution 

 that a process was devised for making alkali by artificial 

 means. The discovery came about in this way. Some 

 years previously it had been discovered that the base of 

 common salt was the same as that of mineral alkali, and 

 in 1775 Scheele, the poor apothecary's assistant who 

 did more for the progress of science than almost any 

 man before or since, had found that litharge would 

 convert common salt into caustic soda. About this 

 time the French Academy of Science oft'ered a prize 

 for a method by which salt could be converted economi- 

 cally into soda. The successful competitor was Nicolas 

 Leblanc, and his process, with a few modifications, is 

 in use at the present day. Nicolas Leblanc, like all 

 the great benefactors of humanity, got little out of it 

 himself. He secured a patent and commenced operations 

 at St. Denis. His patron, the Duke of Orleans, however, 

 was executed in 1793, and Leblanc's works were closed ; 

 whilst in 1791 a decree of the Committee of Public Safety 

 deprived Leblanc of his patent for the benefit of his 

 country, the magnificent sum of six hundred francs being 

 awarded to him by way of compensation. The works were 

 restored to him in 1801, but his capital was gone and he 

 was unable to make headway agamst competitors who 

 were using his invention. In 1806 a committee reported 

 on his case, but the sum awarded to him was so trivial 

 that Leblanc, in despair, committed suicide. 



In converting common salt into caustic soda its atom 

 of chlorine must be replaced by the elements of water, and 

 carbonic acid must be added to this to produce washing 

 soda or carbonate of soda. What is ordinarily called car- 

 bonate of soda is the bicarbonate, which contains twice 

 as much carbonic acid as washing soda. In the Leblanc 

 process the salt is first treated with sulphuric acid, which 

 causes an interchange, the elements of sulphuric acid taking 

 the place of the chlorine to form sulphate of soda or Glaubjr's 

 salts, whilst the chlorine is carried ofif in the gaseous form as 

 hydrochloric acid. This acid is now condensed in water 

 instead of being allowed to escape into the open air to 

 blight the whole surrounding country as it used to do, 

 and in its uupurified form is ciUed muriatic acid or spirits 

 of salt. From this acid the chlorine is recovered and 

 passed through chambers containing lime to make bleaching 

 powder. The sulphate of soda is mixed with chalk and 

 tine coal and heated in a revolving furnace. In the end 

 this produces a solution of carbonate of soda, and the 

 sulphur in the tank waste is nearly all recovered. To make 

 the soda crvstals used for washing clothes this is evapo- 

 rated down by the waste heat from the furnace. If soda 

 ash is required, a much stronger heat is applied to deprive 

 the crystals of the water they contain ; and if caustic soda 

 is wanted, the solution is boiled with lime. 



For many years the Leblanc process had the whole field 

 to itself, but now it has a hard struggle to compete success- 

 fully with the ammonia soda process. The principle of 

 this method is said to have been known since 1S22, but 

 although many worked :it it the engineering diflicuUies 

 proved too formidable, and it was not until about 1863 

 that the problem was solved by a Belgian chemist named 

 Solvay. For many years after that the process did not 

 seem to gain much ground, but since ]n7"2 it has been 

 making great strides, so that by this time nearly as much 

 alkali is made by the ammonia process as by that of 

 Leblanc. The principle of the ammonia process is very 



