October 13, 1923] 



NA TURE 



537 



Letters to the Editor. 



\The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, nor to correspond with 

 the writers of rejected manuscripts intended for 

 this or any other part of NATURE. No notice is 

 taken of anonytnous communications.^ 



The Micelle — -A Question of Notation. 



There is a class of colloids, recognised as a class 

 for very many years, in which the substance is a salt 

 of an ordinary ionisable type the peculiarity of which 

 consists simply \\\ a prodigious disparity in size and 

 solubility between the two parts of the salt molecule. 

 Such are many proteins, some dyes, and soaps, to 

 enumerate them in the order in which they have been 

 investigated. What all colloids do surreptitiously, 

 namely, take to themselves uncovenanted ions, these 

 do in an honest straightforward chemical fashion. 



The properties of the class qua colloids were, I 

 believe, first worked out by myself in the years 1898- 

 1905, the special case examined being certain proteins, 

 called globulins, which present the added complexity 

 that they combine not only with acids and alkaUes to 

 form salts, but also with neutral salts themselves. 

 In spite of this, when the large number of variables 

 was disentangled, the behaviour of the substances was 

 found to be singularly orderly, the phase-rule diagram, 

 for example, being strikingly like that of a common- 

 place three-component system bearing no suspicion of 

 colloidality. 



These colloid salts present one striking peculiarity, 

 namely, that though in water they ionise and hydro- 

 lyse on the whole according to the approved pattern, 

 yet one of the molecular species, and that the one 

 which confers upon the solution its most characteristic 

 qualities, is a complex composed for the most part of 

 undissociated salt molecules but with a surface electric 

 charge due to ionisation at the surface.^ To these 

 bodies I gave the name " colloidal ions." This is 

 strictly accurate notation, for it is because of these 

 complexes that the solutions possess the characteristic 

 colloidal trick of slurring over the obligations of the 

 chemical law of definite and multiple proportions, 

 and they are ions as Faraday used the word, for they 

 wander (Wj') in an electric field. 



I pointed out that they conformed to Helmholtz's 

 analysis of the condition of electric endosmose, the 

 density of the charge on the surface being constant, 

 and the total charge, therefore, proportional to the 

 surface area. This, of course, obtains only when the 

 solution has had time to forget its past history and to 

 come into equilibrium ; waiting for whicli state needs, 

 in colloidal society, a vast gift of patience. 



In the years which followed, much excellent work 

 was done on another example of the group, namely, 

 Congo red, by Bayliss, who described aggregates of 

 anions, the total charge being the sum of the charges 

 of the constituents ; and still later, a third example, 

 namely, ordinary soap, was investigated by McBain, 

 who rediscovered the colloidal ion but christened it 

 " micelle." 



Now accuracy of notation is the breath of the life 

 of science, and to use the word " micelle " for a 

 colloidal ion seems to me to be positively wrong, since 

 the word was introduced by the botanist NiigeU in 

 1877 to describe something entirely different. Nageli 

 was a man of a curious imagination but he clothed his 

 dreams in exact language. He is precise as to what 

 he means by " micelle." The word was coined amid 



' A most interesting suggestion as to their stnirfure is that of Adam, 

 in the Proc. Roy. Soc, A, xcix. 336, 1921. 



a controversy which raged in the 'seventies and 

 'eighties concerning a distinction then drawn between 

 organised and unorganised colloids and the causes of 

 " swelling." 



Nageli, who was an intellectual heir of the Franken- 

 heim of 1851, began with molecules in 1858, but by 

 1877 he had identified the unit of the colloidal state 

 as an aggregate of composite type to which he gave 

 the name " micelle." This he supposed to consist of 

 a nucleus of solute surrounded by an atmosphere of 

 bound water. The water atmosphere was the essence 

 of his conception, which had nothing to do with electric 

 charges or with ionisation. A single " micelle," or a 

 micellar chain, contained a micellar nucleus, or nuclei 

 and micellar water. A gel was conceived as being 

 composed of such chains with their micellar water, 

 disposed as membranes or bars to form a sponge 

 enclosing extra- micellar or " enclosed " water. 



In complete opposition to Nageli was Strasburger 

 (1882), a molecularist in the direct line of descent 

 from Kekule. Between stood Pfeffer, whose forebears 

 were Dutrochet, 1827, Nageli of 1858, Graham, 1864, 

 and Traube, 1867 ; van Bemmelen had no kinship 

 with Strasburger, he follows on the latest stage of 

 Nageh (1880) and Pfeffer. 



I have just been looking through my thirty-year- 

 old notes of that discussion. What a lot those people 

 knew which is now forthcoming as new knowledge ! 

 They knew, or at any rate conjectured, that the 

 colloidal particles were strung together in thread-like 

 masses in some colloidal solutions, and it will do no 

 harm to remind those who propound theories of gel 

 structure that they knew such theories must account 

 for hydrostatic pressures of upwards of 45 atmospheres. 



The colloidal ion is far removed from Nageli's 

 " micelle " ; it is nearer to the supposed colloidal unit 

 which Pfeffer called a " tagma," and described as an 

 overgrown aggregate of one species of molecule, 

 namely, those of the solute. 



Had recent workers known of these earlier hypo- 

 theses they would possibly have been content with the 

 words " colloidal ion " for the constitution of soaps. 

 That brings me to the gist of the matter : in the early 

 'nineties when, as a physiologist, I was attracted to 

 colloids, I found two schools, both of whom had done 

 excellent work, wholly unacquainted with each other's 

 writing. Ringer, for example, on the biological side 

 had demonstrated on the living heart the differential 

 action of ions and " antagonism." He did not 

 recognise the full significance of his observations 

 because, like all contemporary biologists, he was 

 wholly ignorant of the work of Schulze, and of Picton 

 and Linder. The two schools presently came together 

 to the advantage of both, but now the striking want 

 of acquaintance by many chemists with colloidal work 

 published in the biological journals is symptomatic of 

 a renewed falling apart. How many physicists or 

 chemists know of Mines's brilliant work on membrane 

 potential ? 



It is impossible to avoid rediscoveries in science 

 because of the enormous burden of knowledge, but it 

 is in every one's interest to minimise them. Out of 

 the mouth of a sinner comes, I hope, good advice. I 

 must be the greatest of sinners myself, for it is certain 

 that no one reads other people's science with greater 

 reluctance than I do. W. B. Hardv. 



NO. 2815, VOL. I 12] 



Problems of Hydrone and Water : The Origin of 

 Electricity in Thunderstorms. 



The subject of the electricity of rain and its origin 

 in thunderstorms was dealt with by Dr. G. C. Simpson 

 in a communication to the Royal Society in 1909 

 (Phil. Trans., 1909, A, vol. 209, pp. 379-413). Taking 



