September 17, 1896J 



NA TURE 



475 



be oscillatory, and with an undamped vibrator the average 

 velocity would be zero ; we used, therefore, a heavily damped 

 vibrator, with which the average velocity might be expected to 

 be finite. The experiments are not complete, but so far the 

 results are entirely negative. We also tried by the same method 

 to sec if we could detect any movement of the ether in the 

 neighbourhood of a vacuum-tube emitting Rontgen rays, but 

 could not find any trace of such a movement. Prof. Threlfall, 

 who independently tried the same experiment, has, I believe, 

 arrived at the same conclusion. 



Unless the ether is immovable under the mechanical forces 

 in a varying electro-magnetic field, there are a multitude of 

 phenomena awaiting discovery. If the ether does move, then 

 the velocity of transmission of electrical vibrations, and there- 

 fore of light, will be afi'ected by a steady magnetic field. Such 

 a field, even if containing nothing but ether, will behave to- 

 wards light like a crystal, and the velocity of propagation will 

 depend upon the direction of the rays. A similar result would 

 also hold in a steady electric field. We may hope that ex- 

 periments on these and similar points may throw some light on 

 the properties of that medium which is universal, which plays 

 so large a part in our explanation of physical phenomena, and 

 of which we know so little. 



SECTION B. 



CHEMISTRY. 



Opening Address by Dr. Ludwig Mond, F.R.S., 

 President of the Section. 



In endeavouring to fix upon a suitable theme for the address 

 I knew you would to-day expect from me, I have felt that I 

 ought to give due consideration to the interests which tie this 

 magnificent city of Liverpool, whose hospitality we enjoy this 

 week, to Section B. of the British Association. 



I have therefore chosen to give you a brief history of the 

 manufacture of chlorine, with the progress of which this city 

 and its neighbourhood have been very conspicuously and very 

 honourably connected, not only as regards quantity — I believe 

 this neighourhood ]>roduces to-day nearly as much chlorine as 

 the rest of this world together — but more particularly by having 

 originated, worked out, and carried into practice several of the 

 most important improvements ever introduced into this manu- 

 facture. I was confirmed in my choice by the fact that this 

 manufacture has been influenced and perfected in an extra- 

 orilinary degree by the rapid assimilation and application of the 

 results of purely scientific investigations, and of new scientific 

 theories, and offers a very remarkable example of the incalculable 

 value to our commercial interests of the progress of pure science. 



The early history of chlorine is particularly interesting, as it 

 played a most important role in the development of chemical 

 thecjries. There can be nij doubt that the Arabian alchemist 

 Geber, who lived eleven hundred years ago, must have known 

 that " AquaRegia," which he prepared by distiUing a mixture of 

 salt, nitre, and Wtriol, gave off, on heating, very corrosive, evil- 

 smelling, greenish-yellow fumes ; and all his followers through- 

 out a thousand years must have been more or less molested by 

 these fumes whenever they used Aqua Regia, the one solvent of 

 the gold they attempted so persistently to produce. 



But it was not until 1774 that the great Swedish chemist 

 Scheele succeeded in establishing the character of these fumes. 

 He discovered that on heating manganese with muriatic acid he 

 obtained fumes very similar to those given off by " Aqua Regia," 

 and fiumd that these fumes constituted a permanent gas of 

 yellowish-green colour, very pungent odour, very corrosive, very 

 irritating to the respiratory organs, and which had the power of 

 destroying organic colouring matters. 



According to the views prevalent at the time, Scheele con- 

 sidered that the manganese had removed phlogiston from the 

 muriatic acid, and he consequently called the gas dephlogisticated 

 muriatic acid. 



When, during the next decade, Lavoisier successfully attacked, 

 and after a memorable struggle completely upset the phlogiston 

 theory, and laid the foundations of our modern chemistry, 

 BerthoUet, the eminent "father" of physical chemistry — the 

 science of to-day — endeavoured to determine the place of Scheele's 

 g.as in the new theory. Lavoisier was of opinion that all acids, 

 including muriatic acid, contain oxygen. BerthoUet found that 

 a solution of .Scheele's gas in water, when exposed to the sun- 

 light, gives off oxygen and leaves behind muriatic acid. He 



NO. 1403, VOL. 54] 



considered this as proof that this gas consists of muriatic > acid 

 and oxygen, and called it oxygenated muriatic acid. 



In the year 1785 BerthoUet conceived the idea of utilising the 

 colour-destroying powers of this gas for bleaching purposes. He 

 prepared the gas by heating a mixture of salt, manganese, and 

 vitriol. He used a solution of the gas in water for bleaching, 

 and subsequently discovered that the product obtained by 

 absorbing the gas in a solution of caustic potash possessed 

 great advantages in practice. 



& This solution was prepared as early as 17S9, at the chemical 

 works on the Quai de Javelle, in Paris, and is still made and 

 used there under the name of ' ' Eau de Javelle. " 

 \< James Watt, whose great mind was not entirely taken up with 

 that greatest of all inventions — his steam-engine — by which he 

 has benefited the human race more than any other man, but who 

 also did excellent work in chemistry — became acquainted in Paris 

 with BerthoUet's process, and brought it to Scotland. Here it 

 was taken up with that energy characteristic of the Scotch, and 

 a great stride forward was made when, in 1798, Charles Tennant, 

 the founder of the great firm, which has only recently lapsed into 

 the United Alkali Company, began to use milk of lime in place 

 of the more costly caustic potash, in making a bleaching liquid ; 

 and a still greater advance was made when, in the following 

 year, Tennant proposed to absorb the chlorine by hydrate of 

 lime, and thus to produce a dry substance, since known under 

 the'-iname of bleaching powder, which allowed the bleaching 

 powers of chlorine to be transported to any distance. 



In order to give you a conception of the theoretical ideas pre- 

 valent at this time, I will read to you a passage from an interest- 

 ing treatise on the art of bleaching published in 1799 by Higgins. 

 In his chapter " On bleaching with the oxygenated muriatic 

 acid, and on the methods of preparing it," he explains the theory 

 of the process as follows : — 



" Manganese is an oxyd, a metal saturated with oxygen gas. 

 Common salt is composed of muriatic acid and an alkaline salt 

 called soda, the same which barilla affords. Manganese has 

 greater affinity to sulphuric acid than to its oxygen, and the soda 

 of the salt greater affinity to sulphuric acid than to the muriatic 

 acid gas ; hence it necessarily follows that these two gases (or, 

 rather, their gravitating matter) must be liberated from their former 

 union in immediate contact with each other ; and although they 

 have but a weak affinity to one another, they unite in their 

 n>ascent state, that is to say, before they individually unite to 

 caloric, and separately assume the gaseous state ; for oxygen gas 

 and nuiriatic acid gas already formed will not unite when mixed, 

 in consequence principally of the distance at which their respective 

 atmospheres of caloric keep their gravitating particles asunder. 

 The compound resulting from these two gases still retains the 

 property of assuming the gaseous state, and is the oxygenated 

 muriatic gas." 



Interesting as these views may appear, considering the time 

 they were published, you will notice that the rile played by the 

 manganese in the process, and the chemical nature of this sub- 

 stance, were not at all understood. The law of multiple pro- 

 portions had not yet been propounded by John Dalton, and the 

 researches of Berzelius on the oxides of manganese were only 

 published thirteen years later, in 181 2. The green gas we are 

 considering was still looked upon as muriatic acid, to which 

 oxygen had been added, in contradistinction to Scheele's view, 

 who considered it as muriatic acid, from which something, viz. 

 phlogiston, had been abstracted. 



It was Humphry Davy who had, by a series of brilliant investi- 

 gations, carried out in the laboratory of the Royal Institution 

 between 1808 and 1810, accumulated fact upon fact to prove that 

 the g.as hitherto called oxygenated muriatic acid did not contain 

 oxygen. He announced in an historic paper, which he read be- 

 fore the Royal Society on July 12, iSio, his conclusion that this 

 gas was an elementary body, which in muriatic acid was com- 

 bined with hydrogen, and for which he proposed the name 

 "chlorine," derived from the Greek x^^pifs- signifying 

 "green," the colour by which the gas is distinguished. 



■Phe numerous communications which Humphry Davy made 

 to the Royal Society on this subject form one of the brightest 

 and most interesting chapters in the history of chemistry. They 

 have recently been reprinted by the Alembic Society, and I can- 

 not too highly recommend their study to the young students of 

 our science. 



Those who have followed the history of chemistry I need not 

 remind how hotly and persistently Davy's views were combated 

 by a number of the most eminent chemists of his time, led by 



