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NATURE 



■{July 1 8, 1889 



hypothesis of electrolytic dissociation. At first sight 

 one is shocked by being told that a very strong 

 acid such as nitric acid, or a very strong base such as 

 potash, is dissociated in aqueous solution, to perhaps 90 

 per cent., into its ions ; in the case of potash, one remarks 

 thatthe ionsmust be potassium and the group OH, and that 

 each of these bodies reacts with water the moment they 

 are brought into contact. To meet these objections, 

 Ostwald reminds us that a chemically energetic com- 

 pound is one which readily suffers chemical change, and 

 the parts of which are therefore readily separated ; and he 

 remarks that the ion potassium is not the same thing as 

 ordinary potassium ; the ion holds a large electric charge ; 

 when it comes to the electrode it gives up this charge, 

 and then, but not till then, it reacts with water. But 

 difficulties still remain : one of the greatest is to explain 

 the mode of action of the solvent. Does the solvent 

 merely form a medium in which the separate ions move 

 about ? Why then does increase of solvent increase the 

 amount of dissociation ? May not the solvent react 

 with the dissolved body to form complex molecular 

 aggregates which then dissociate into simpler ions? Is 

 the dissolved body the electrolyte, or is the electrolyte a 

 compound, or aggregate, made up of the dissolved body 

 and the solvent ? 1 s the electrolyte actually separated into 

 its ions in the solution, or does it only exhibit an "apti- 

 tude for directed dissociation " ? These questions, and 

 •questions such as these, have yet to be answered. 



The hypothesis of electrolytic dissociation has been 

 v.'orked out in detail in several directions, by Arrhenius 

 and Ostwald, and has been found to give results in keep- 

 ing with experiment. In considering its application to 

 explain chemical change between electrolytes — for it really 

 presents a theory of chemical changes between electrolytes 

 —it is necessary to remember that, in its present form at 

 any rate, it is applicable only to substances in aqueous 

 solution. Because a solution of hydrochloric acid is very 

 chemically active, it does not follow that liquid HCl 

 should also be chemically energetic ; nor, because gaseous 

 HCl is not dissociated by heating to a fairly high tem- 

 perature, does it follow that an aqueous solution of this 

 compound should not be largely dissociated into the ions 

 hydrogen and chlorine. 



The hypothesis of chemical change between electro- 

 lytes in solution, which is based on van 't Hofl:"'s extension 

 of the law of Avogadro to substances in dilute solutions, 

 and on the general close agreement between such dilute 

 solutions and gases, cannot yet be finally accepted or 

 rejected by chemists. It has already done much to draw 

 closer the connexions between chemical and electrical 

 phenomena, it has gone further than any other hypothesis 

 of chemical change in helping forward the solution of the 

 main problem of chemists, and it has opened up many 

 new lines of advance. 



There is one general conclusion to be come to from the 

 study of all the recent work on chemical affinity : I think 

 we may agree with Ostwald when he says that Bergmann 

 was certainly right in assigning a definite affinity to each 

 , element and compound, and that Berthollet was right in 

 asserting that affinity is modified by the relative masses of 

 the reacting bodies, but that Bergmann erred in saying 

 that chemical change always occurs in one direction only 

 and that the direction of the strongest affinities, while 

 Berthollet also erred in regarding the affinity between 

 acids and bases as inversely proportional to the equivalent 

 weights of the reacting compounds. Bergmann's error has 

 been revived in modern times ; it has now assumed a 

 physico-chemical aspect ; it finds its expression in 

 Berthelot's so-called lazv of maximum work, which asserts 

 that every chemical change accomplished without the 

 addition of energy from v/ithout tends to the formation of 

 that body or system of bodies the production of which 

 is accompanied by the development of the maximum 

 quantity of heat. In so far as this statement can be 



translated into precise terms it can be proved to be dynami- 

 cally unsound. When applied to chemical reactions, it tells 

 us that of several possible reactions that one which is 

 accompanied by the production of the greatest quantity 

 of heat occurs to the exclusion of others ; but this has 

 again and again been experimentally disproved. 



M. M. Pattison Muir» 



THE PASTEUR INSTITUTE. 



LAST week the Lord Mayor received a letter from 

 ' M. Pasteur, acknowledging receipt of the resolu- 

 tions passed at the recent Mansion House meeting. la 

 this letter M. Pasteur writes : — 



'• If the aphorism that science has no country has 

 never received authoritative sanction, it did so at this 

 meeting, in which the leading savants in biological and 

 medical science of the United Kingdom took part. I 

 wish I could thank them individually for having attended 

 this gathering. I was filled with gratitude on learning- 

 that the Prince of Wales himself had accorded his high 

 approbation of your initiative. Modesty compels me to 

 pass over in silence the kind words of which my labours 

 and those of the Pasteur Institute have been the subject, 

 but I have a right to rejoice with all friends of the 

 progress of humanity at the great moral effect of the 

 meeting. The manifestation of July i had not only for 

 its object the question of the treatment and possible 

 extinction of hydrophobia in England, but in the nature 

 of things it was also a protest against that false senti- 

 mentality which led certain persons, not— which was 

 already a strong point with them — merely to put on the 

 sarhe footing the life of men and that of animals, but 

 even to prefer the existence of animals to the salvation of 

 human life. When this view is taken, what is the limit ? 

 We must become firm vegetarians. We must even extend 

 our scruples so that no living being is sacrificed. We 

 must endure the importunities of a mosquito, the daring 

 of a mouse, the stings of a flea — false ideas or excuses 

 for a tirade which one finds is most often at the bottom 

 of all the attacks on experimental physiology. Certain 

 credulous souls — by I know not what tales — imagine that 

 our laboratories are chambers of torture. They ignore 

 the fact that the rabbit or the guinea jiig is rendered 

 insensible by chloroform before it is subjected to the most 

 insignificant operation. As for me personally, the suffer- 

 ing of an animal affects me so much that I would never 

 shoot a bird, and the cry of a wounded skylark pierces 

 me to the heart ; biit if the investigation of the mysteries 

 of Nature and the acquisition of new truths be at stake, 

 the sovereignty of the object justifies all. Who, then, 

 having the least regard for the pursuit of the knowledge 

 of the mysteries of Nature, would put in the balance the 

 sacrifice of a few fowls and rabbits with the discovery of 

 the attenuation of virus and prophylactics which have 

 resulted from such sacrifice ? No one, my Lord Mayor, 

 will have contributed more than you have done to rectify 

 the errors which under a show of compassion can only 

 hinder the progress of science and compromise even the 

 most legitimate interests of humanity." 



THE TERRESTRIAL GLOBE AT THE PARIS 

 EXHIBITION. 



SOME time before the opening of the Paris Exhibition 

 it was announced that one of the attractions of the 

 show would be a great terrestrial globe, one millionth of 

 the actual size of the earth. This globe is now e-xhibited 

 in a building specially erected, near the Eiffel Tower, for 

 the purpose, and it excites the warmest interest among 

 all visitors who have devoted the slightest attention to 

 geographical science. It was designed by MM. Villard 



