March 3, 1H93.] 



SCIENCE. 



115 



cubic equation we find that at the critical point, jt, the critical 

 pressure = Table II. eires the results of this calculation, 



and it will be seen that the values for benzine and NO2 do not 

 coinci'le with the values for n. As the values of a and b were 

 originally calculated from ir, it is evident that some misprint has 

 crept into the tables, and there is little doubt but that if the cor- 

 rect values for a and b were substituted, they would fall into 

 line and that in all cases the quantity a, in Van der Waals' equa- 

 tion, must be taken as equal to a quantity c, which is constant 

 for all gases, multiplied by the atomic volume to the | power. 



4. Electrical conductivity. As before mentioned linked atoms 

 cannot conduct. If we examine the enclosed cube of the ele- 

 ments, we see that the non-conducting elements are found 

 on sides J? and Wol the cube, and these are the elements whose 

 atoms are linked or plexed. We can tell this in the following 

 ways : — 



CUBE OF THE ELEMENTS. 



1st, By their low speciflc heats. Those who are acquainted 

 with chemical phy.'iics will recognize this fact and the necessary 

 deduction. Briefly, if the kinetic energies of all molecules are 

 the same at the same temperature, then if the sulphur molecule 

 in solid sulphur is triatomic, or has its mass three times that of 

 one atom; then since all the + ?K v' s are equal, solid sulphur 

 will only havef the specific heat it would have if the molecule 

 were monatomic (provided that no work is spent in disassociating 

 the molecule.) 



The standard atomic heat is 6.4. The following substances 

 have low specific heats, and are all insulators or poor conductors: 

 Sulphur, 5.4; phosphorus, 5.4; fluorine, 5; silicon, 3.8; carbon, 1.8. 



2d, By their vapor densities. If a substance has a biatomic 

 vapor it is not likely that it will be a monatomic solid. The fol- 

 lowing substances have two or more atoms to the molecule when 

 in the state of vapor: sulphur, iodine, bromine, chlorine, selen- 

 ium, tellurium, phosphorus, arsenic. And these are all insula- 

 tors or poor conductors, while mercury, cadmium, zinc, and 

 sodium have monatomic vapors and are good conductors. 



As regards metals in the allotropic state. Allotropic is a word 

 which has been used to cover a multitude of sins. Every time 

 an erring element goes vs'rong and misbehaves itself by emphasiz- 

 ing some of its previous peculiarities, or developes some new 

 ones, it is stigmatized as "allotropic." For instance, we see it 

 stated that when iron amalgam is strongly heated the iron left 

 behind is allotropic because it takes fire in the air. But such an 

 action does not show that any new property has been developed, 

 it merely emphasizes a fact already well known, i.e., that iron 

 oxidizes when exposed to air. A fine cambric needle will catch 

 fire when held in the flame of a Bunsen burner for a second, and 



will continue to burn like a match after it is withdrawn. When 

 the iron is in a finely divided state, the surface exposed is greater, 

 and, the oxidation per unit of mass being much greater, the tem- 

 perature of the iron is raised much more, thus favoring oxidation 

 still more. 



If, then, we are to use the word allotropic in this sense, we 

 should logically speak of kindling-wood as an allotropic form of 

 timber, for, as fire underwriters know, heavy timber is one of 

 the most fireproof of substances. We might also speak of that 

 form of conscience which large corporations are supposed to 

 possess, as an allotropic conscience. 



If, however, we do apply the word allotropic to such forms as 

 Joule's iron, Cary-Lea's silver, etc., then we need another word 

 to express the changes in the physical behavior of metals which 

 are not due merely to the accenting of known properties but to 

 the development of new properties, due to the joining of two or 

 more atoms of a metal into one molecule. Polymerism might 

 do, but it does not lend itself easily to use, and for myself I pre- 

 fer to use the word plex, and to speak of diplexed iodine, tri- 

 plexed sulphur, and of an element in a plexed form ; though I 

 have no doubt that if Clifford were still with us he would say 

 that two-linked and three-linked are good enough for any honest 

 Anglo-Saxon. 



As regards the conductivity of "allotropic" elements, there is 

 no reason to suppose that the conductivity of Joule's iron is dif- 

 ferent from that of ordinary iron. But when the elements are 

 plexed, as we have seen above, the resistance will be much in- 

 creased and the temperature sufficiently lowered, because heating 

 increases disassociation nearly as fast as it lessens rigidity, or 

 even in the case of those alloys or elements with negative tem- 

 perature coefficients, faster, 



[Note. — "With regard to the previous paper, it may be noted 

 that the explanation of the difference between cohesion and 

 chemical combination, that in cohesion the atoms are charged 

 similarly in every way except as regards position, thus — 



while if any third substance short circuits the atoms they are 

 left chemically combined, thus — 



is also an explanation of a law which will probably be found true 

 in the near future, i.e., no two substances can combine with each 

 other without the presence of a third, thus making all chemical 

 action the result of catalysis, plexed forms of the substances 

 being capable of acting third substances. As regards the short- 

 ening of stretched rubber by heating, it is of course not to be sup- 

 posed that the two parts of India rubber are literally contained 

 one inside a sphere of the other, but that rubber rather resembles 

 a tangled reel of silk embedded in jelly. If we consider any ele- 

 ment of the jelly, and we see that it is bounded on all sides by 

 threads of silk, and that these will act as the cell-wall of the pre- 

 vious paper, only "more so." The heating of rubber when 

 stretched may be explained conversely by the compression of the 

 jelly-substance by the cell-wall substance. E. A. F.] 



THE GROOVE IN THE PETIOLE OF LEAVES. 



BY AVEN NELSON, DNIVEESITT OF WYOMING, LARAMIE, WYOMING. 



In the spring of 1893, I had the pleasure of making some ob- 

 servations and brief studies, in conjunction with Mr. H. L. Jones, 

 upon the origin and more particularly the function of the groove 

 found in the petiole of many leaves, especially of Endogens. 



