28 



KNOWLEDGE. 



[Febkuary 1, 1893. 



chemicals depends entirely on their state of purity, this 

 gives the ammonia-soda process a distinct advantage. 



The history of the up-hill struggle made by the wet 

 process before attaining to its present position would form 

 an interesting narrative in itself. Engineering difficulties 

 of every imaginable kind had to be overcome ; in fact, the 

 leakage of ammonia at one time was so unaccountable 

 that the chemists in charge were almost reduced to despair, 

 and began to formulate new theories of chemical action to 

 accoimt for the missing molecules. Technical skill of the 

 highest order, apphed to every detail, and dogged per- 

 severance in the face of heart-breaking obstacles, at last 

 succeeded, and, for the last ten years, the ammonia-soda 

 process has been gaining ground rapidly. 



In both cases, alkali has not been the only product of 

 the chemical reactions involved in the manufacture. Salt 

 consists of chlorine as well as sodium, and its profitable 

 utilization is the key of the disputed position. The 

 Leblanc soda makers can turn a large proportion of their 

 chlorine into bleaching powder and similar compounds, but 

 the ammonia-soda makers have found no satisfactory means 

 at present of utilizing theirs. Comparatively recently, all the 

 hydrochloric acid, formed by the action of sulphuric acid 

 on salt in the first part of the operations, used to pass into 

 the air unchecked, to the great injury of every form of life. 

 Now, the gases from the decomposing pots are passed 

 through coke towers, down which a stream of water trickles, 

 and less than five per cent, is allowed to escape. Chlorine, 

 indeed, has become very valuable. It is the active prin- 

 ciple of nearly all bleaching compounds, and an important 

 constituent of chlorate of potash, largely used in fireworks. 

 All the different ways of converting hydrochloric acid into 

 chlorine are the same in principle — the hydrogen is burnt 

 and the chlorine set free. In the venerable Weldon 

 process, the necessary oxygen is supplied by a high oxide 

 of manganese ; in Deacon and Hurter's method the acid is 

 mixed with air and passed over clay impregnated with a 

 copper salt which acts as a go-between ; and in yet 

 another, nitric acid is the carrier of oxygen. The chlorine 

 of the salt used in the ammonia-soda process goes to form 

 ammonium chloride, as previously mentioned. When this 

 is heated with hme to get back the ammonia the chlorine 

 is converted into calcium chloride, from which it does not 

 pay to recover it at present, although attention has been 

 concentrated on the subject for a long while. In 18a8 

 Messrs. Weldon and Pechiney invented a system for 

 recovering chlorine from chloride of magnesium. This 

 caused the greatest alarm for a time amongst our home 

 manufacturers, for at the salt mines of Stassfurt 200,000 

 tons of magnesium chloride, containing 50,000 tons of 

 chlorine, are thrown away every year. They feared that, 

 if this could be worked up by the new method, the whole 

 chlorine industry would be diverted to Germany. The 

 high temperature (1000° C.) required in the Weldon- 

 Pechmey process, however, played havoc with the plant, 

 and the anticipations of its promoters have not been 

 realized. Similar methods are being tried for utilizing 

 the chlorine of the ammonia-soda process, but so far 

 unsuccessfully. 



The third process for the production of alkah is by 

 means of electricity. When a current of electricity is 

 passed through a solution of salt, sodium hydrate (NaOH) 

 and free chlorine are produced. Electricity is, therefore, 

 the ideal weapon for breaking up the salt, in theory. In 

 practice, unfortunately, many difficulties arise. If the 

 current passes through the solution without a diaphra^an 

 between the poles, the separated atoms re-combine to a 

 large extent. If, on the other hand, a wall is introduced 

 to keep the products apart, the resistance is increased 



enormously. The possibility of making soda and chlorine 

 by electricity turns on the invention of a diaphragm, which, 

 whilst separating the newly formed atoms, will not add 

 largely to the resistance of the circuit. Messrs. Cross and 

 Bevan, in their recent paper at the Society of Chemical 

 Industry, describe a very ingenious diaphragm, by the 

 help of whish they claim that the electrical method can be 

 worked successfully. They state that in America it is 

 already in operation on a large scale, the chlorine produced 

 being used for bleaching paper. 



The successful method must ultimately be the one 

 requiring the smallest expenditure of chemical energy, and 

 which can make use of the cheapest available form. In 

 the electrical process, for instance, the loss in converting 

 the energy of the coal first into heat, then into electricity, 

 and finally into chemical energy, may prove greater than 

 in the Leblanc process, where the energy is used directly in 

 the form of heat. In addition, every constituent of the 

 raw materials must be recovered, or in other words, there 

 must be no waste products. 



Hftttts 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



HABITS OF THE riCHlCtACIO. 



To the Editor of Knowledge. 



Sir, — I regret to find that in my article in the December 

 number I was misled by the artist as to the habits of the 

 Pichiciago. The creature does not, as depicted on page 222, 

 creep under rocks, but always inhabits sandy districts ; 

 and it has been suggested that the use of the shield at the 

 hinder extremity is to act as a rammer in securely closing 

 the entrance to its burrow with sand. It should also have 

 been stated that the tail protrudes through a notch in the 

 lower border of this shield, and not through a hole in the 

 centre. R. Lvdekker. 



THEORY OF THE SUN. 

 To tlie Editor of Knowledge. 



Sir, — As in the last number of your magazine you have 

 kindly obliged me with the enumeration of some objections 

 to my explanation of the prominences as merely (Evanescent 

 Hhmiineitiona earned by the ■propaijtHion nf clieiiiical aetion in 

 eoinjKinitireli/ tramiuH nuttter, I hope you will allow me to 

 state briefly what are the most important facts seeming to 

 me in contradiction with the hypothesis of actual motion 

 in prominences, and fully agreeing with my quite different 

 explanation. 



1°. We have the inuUstuilied xti-ntijieation of the xo/ar 

 iitiiiosjdteie, which, though continually crossed by the 

 prominences, retains its heavier gaseous components firmly 

 at its bottom. Now, we know that movements a thousand 

 times slower than those of the supposed solar storms are 

 already quite sufficient to impede the least trace of stratifi- 

 cation in our terrestrial atmosphere. 



2°. We have the stratijieation of the proiiiinenres tlieinsclees, 

 never carrying the heavier metallic vapours they often 

 contain at their bases to those greater heights where they 

 consist almost only of hydrogen, helium, and some lighter 

 metals as Na, Mg, and Ca. 



'd\ We have the ili.-iSohiiin-eifir-e/Kiraeler nf imnii/ prniiii- 

 iiences, almost instantaneously arising, continually altering 

 their forms and, though big as some dozens of earths, 

 sometimes vanishing iu the space of a few minutes. 



