572 



NA TURE 



[April 14, 18S7 



is very similar to that of acids ; abundant proof of this is afforded 

 especially by F. Kohlrausch's refined measurements, of which an 

 account has recently been published ( WieJ. Ann., 1886, xxvi., p. 

 162). I venture to think that a similar explanation to that above 

 given for oxides will apply to salts ; and alsj that the 1 jw mole- 

 cular conductivities of salts as compared with corresponding 

 acids may be regarded as confirmatory of my hypothesis. I 

 think we must admit that the metals generally have less affinity 

 than hydrogen for negative radicles ; if this be granted, we have 

 at once an explanation of the fact that metallic salts are mostly 

 fixed solids, few of which are more than moderately soluble 

 in water while many are very diflicultly soluble or insoluble, 

 whereas the corresponding acids are mostly volatile and readily 

 soluble in water, if not miscible with it in all proportions. The 

 affinity of the negative radicles being less exhausted by union 

 with metals than with hydrogen, the fundamental molecules 

 of salts are more prone to unite together to form complex 

 aggregates. 



Arrhenius, who has studied the electrical behaviour of solu- 

 tions of a number of salts, attributes the change observed in 

 molecular conductivity on dilution — as I have done — to mole- 

 cular changes ; but his deductions are all based on the accept- 

 ance of the Williamson-Clausius hypothesis of dissociation. 



My hypothesis would also account for the increase in con- 

 ductivity in composite electrolytes with rise of temperature. It 

 is true that as temperature rises the influence which individual 

 molecules exert upon each other would be lessened ; but, on the 

 other hand, the complex aggregates would become more and 

 more completely resolved into their fundamental molecules, the 

 velocity of molecular motion would increase, and the tendency 

 of the constituent atoms to remain united would be lessened. 

 From this point of view the determination of the coefficient of 

 change of conductivity with temperature in the case of sub- 

 stances whose molecular conductivity increases considerably on 

 dilution in comparison with allied compounds which exhibit only 

 a slight variation in molecular conductivity on dilution affords an 

 interesting subject for investigation. F. Kohlrausch has already 

 pointed out (Pogg. Ami., 1875, cliv., p. 236) that in the case of 

 all neutral salts, "der Einflussder Temperatur auf das Leitungs- 

 vermogen mit wachsender Verdiinnung sich Anfangswerthen 

 nahert, die zwischen engen Griinzen liegen ;" and the experiments 

 of F. Kohlrausch and Nippoldt on solutions of sulphuric acid 

 (ibid., 1869, cxxxviii,, p. 286) show that the resistance diminishes 

 to a much greater extent for equal increments of temperature in 

 concentrated than in dilute solutions. 



As concentrated solutions would be richer in complex aggre- 

 gates than dilute solutions, these results are in entire ac- 

 cordance with my hypothesis : it does not appear to me that 

 they can be satisfactorily interpreted in terms of the dissociation 

 hypothesis. 



In cases where the influence of the one member of the com- 

 posite electrolyte upon the other is but slight, it may happen 

 that the effect of temperature in diminishing this influence will 

 outweigh that due to molecular simplification, and that, in con- 

 sequence, conductivity will diuinish with rise of temperature ; a 

 mixture of alcohol and ether would appear to furnish an example 

 of this kind : according to Pleiffer's recent observations ( Ificd. 

 Ann., 18S6, xxvi., p. 216), such a mixture behaves as a metallic 

 conductor of very high resistance. 



The increase in conductivity of graphite and gas-retort carbon 

 on heating, and the effect of light on the conductivity of (? impure) 

 selenium and some other substances (Shelford Bidwell, Phys. 

 Soc. Proc, pp. 122, 256), appear to me to be also explicable on 

 the assumption that m all these cases we are dealing with 

 composite electrolytes. 



If any further proof be needed of an intimate connexion 

 between molecular composition and electrolytic conduction, it 

 is most conclusively afforded, I think, by the observations of 

 W. Kohlrausch on chloride, bromide, and iodide of silver ( ll'icii. 

 Ann, 1882, xvii., p 642). In the fused state, these compounds 

 are better conductors than the most highly-conducting mixture 

 of sulphuric acid and water, which of all liquids is the best con- 

 ductor at ordinary temperatures, but when the change from the 

 fused to the solid state sets in the resistance of both silver 

 chloride and bromide suddenly increases. No such change takes 

 place, however, in the case of silver iodide. This iodide fuses 

 at 557° according to Rodwell, but at about 540° according to 

 Kohlrausch ; its electrical resistance increases only gradu.ally 

 after it has becoaie solid, and remains alinost a linear function 

 of the temperature during an interval of 400°, until suddenly at 



near 150° it increases enormously, this change taking place at 

 the moment when, according to Rodwell (Phil. Trans., 1882, 

 p. 1 153), it passes from the transparent, plastic, amorphous 

 solid to the opaque, crystalline state, the volume increasing 

 considerably. Kohlrausch has proved most conclusively that 

 the sohd iodide may undergo electrolysis. It would seem that 

 almost immediately after solidification in the case of silver 

 chloride and bromide practically the whole mass consists of 

 complex aggregates so constituted as to be exceedingly bad 

 conductors, but that such aggregates are formed much less 

 readily by silver iodide. 



( To be continued. ) 



THE MAZAPIL METEORIC IRON^ 

 A MONG the large nuinber of meteoric irons which have been 

 ■^ described, only eight - are recorded as having been seen 

 to fall. It is my privilege to be able to add a ninth fall to this 

 short list, and one which may prove to be of exceptional scientific 

 importance. This mass of meteoric iron I received in August 

 last as a gift from my friend, Prof. Jose A. y Bonilla, Director 

 of the Astronomical Observatory at Zacatecas, Mexico. He 

 stated that it was seen to fall at about 9 p.m. on November 27, 

 1885, during the periodical star-shower of the " Bielids." 

 Such is the unique interest of this meteorite, as shown by its 

 history, that I have delayed announcing it until the evidence of 

 its fall had been substantiated as thoroughly as possible. 



The general freshness of surface, which shows very perfectly 

 the flow of the melted crust ; the presence of unusually large 

 nodules of a very compact graphite ; the very slight superficial 

 oxidation, and its dissimilarity to other meteorites of the region, 

 are all interesting features of this iron, and serve to confirm the 

 statement of its recent fall. When received it weighed about 

 3950 grammes. Its present weight is 3864 grammes, or 10 pounds 

 4^ ounces, troy. Its greatest length is 175 millimetres as 

 measured diagonally across the mass. In its thickest part it 

 measures about 60 millimetres. It could be described as a flat 

 irregular mass, covered with deep depressions, having a smooth 

 surface (see Fig. l). 



The evidence of the fall is set forth in the following com- 

 munication from Prof. Bonilla. 



(Translation). — " It is with great pleasure that I send to you 

 the uranolite which fell near Mazapil, during the night of 

 November 27, 1S85. That you may the better appreciate the 

 great scientific interest which this uranolite possesses, I will 

 state that everything points to the belief that it belongs to a 

 fragment of the comet of Biela-Gambart, lost since 1852. I 

 here give you the history of this celestial wanderer. On 

 December 2 (1885) I received, to my great delight, from 

 Eulogio Mijares, who lives on the Conception Ranch, 13 kilo- 

 metres to the east of the town of Mazapil, a uranolite, which he 

 saw fall from the heavens, at nine o'clock on the evening of 

 November 27, 1885. The fall, simply related, he tells as 

 follows, in his own words : — 



" ' It was about nine in the evening when I went to the corral 

 to feed certain horses, when suddenly I heard a loud hissing 

 noise, exactly as though something red-hot was being plunged 

 into cold water, and almost instantly there followed a somewhat 

 loud thud. At once the corral was covered with a phos- 

 phorescent light and suspended in the air were small luminous 

 sparks as though from a rocket. I had not recovered from my 

 surprise when I saw this luminous air disappear and there re- 

 mained on the ground only such a light as is made when a match 

 is rubbed. A number of people from the neighbouring houses 

 came running toward me and they assisted me to quiet the horses 

 which had become very much excited. We all asked each other 

 what could be the matter, and we were afraid to walk in the 

 corral for fear of getting burned. When, in a few moments, we 

 had recovered from our surprise, we saw the phosphorescent 

 light disappear, little by little, and when we had brought lights 

 to look for the cause, we found a hole in the ground and in it a 

 ball of fire. We retired to a distance, fearing it would explode 



From the March number of the An 



■ PP- 



26. 



^ Jo. 



at 0/ Scie. 



^ Agram. Croatia. May 26, 1751 : Charlotte. Dickson Co., Tenn., August 

 I, 183s ; Braunau. Bohen.ia, July 14, 1847 : Tabarr, Saxony, October 18. 

 1S54; Victoria West, Africa, in 1S62 : Nejed. Arabia, spring of 1865 ; 

 Nedagolla, Ind.a. January 23, 1870 ; Rowton. Shropshire, England, April 

 20. 1876. f^ee the Catalogue o the Meteontes in the Mineral Dep.irtment of 

 the British Museum, by L. Fletcher, p. 42. 



