Nov. 6, 1873J 



NATURE 



prominently brought before our notice, it may perhaps seem 

 premature to pursue its action further back in the history of the 

 universe. However, it seems but natural that we should apply 

 this hypothesis to explain the close connection that holds be- 

 tween certain of the so-called elements. Pre-supposing that this 

 theory has not been discussed before, I will just mention the chief 

 grounds for holding it, and leave tlie examination into its truth 

 or falsity in tlie hands of more experienced chemists. Herbert 

 Spencer defines evolution as the integration of matter at the 

 expense of force ; this integration being accompanied by a loss 

 of polarity, and by specialisation in a certain direction. Thus 

 much being granted let us see how far this change from simple 

 to complex is traceable in the qualities of certain of the 

 elements, as seen especially in those that fall under natural 

 groups. 



In the first place, we may call some of the metals more gene- 

 ralised than others. Thus all hydrogen salts are soluble in 

 water ; so, to a less extent, are those of lithium, sodium, and 

 potassium ; but as the atomic weight (or mass) increases, so tlie 

 salts of those metals become less and less soluble. This is only 

 true speaking generally, for we see that, in particular cases, the 

 hydrate of barium is more soluble in water than that of cal- 

 cium, &c. But, as a rule, the salts of barium are less soluble 

 than those of strontium ; these, again, than calcium salts. But, 

 on the whole, we may say that with increase of atomic mass of 

 the metals, their salts lose their general properties and become 

 more ami more specialised, the salts taking their character irom 

 the metal in combination. 



Secondly, according to this hypothesis, increase of atomic 

 mass should be accompanied by absorption of motion. Just as 

 the very complex molecules, of which living organisms are built 

 up, are deficient in polarising or crystallising force, so are also 

 the more massive chemical atoms : for it is evident that the 

 heavy atoms of le.id and bismuth have far less of this force, called 

 chemical affinity, than have the light sodium, or the still lighter 

 hydrogen atoms. In colloid bodies, the atomic attractions are 

 mostly used up in keeping together the comparatively great 

 masses of the molecule : hence but little polarity, or attraction 

 among the molecules themselves, is manifested, and the com- 

 pounds from the union of these molecules are unstable. So, too, 

 the more massive atoms of elements enter with more difficulty 

 into combination, and the products formed are unstable. Thus, 

 the chlorides of platinum, or the oxides of lead, &c., are less 

 stable, and more difficult of formation, than the corresponding 

 salts of potassium or magnesium. Whereas colloids and crys- 

 talloids readily unite toi;ether : this is paralleled by the strong 

 affinity that hydrogen, or any metal, has for chlorine or 

 oxygen. Here the metal is the light crystalloid, the non-metal, 

 the colloid, so to speak. It is only with the more specialised of 

 the metals, those which we have seen have massive atoms, that 

 hydrogen will unite, viz., antimony and arsenic ; and the com- 

 pound it forms with the former is very unstable, whilst the 

 hydride of bismuth is unknown. These compounds are not 

 alloys like that of hydrogen with palladium, but they show the 

 comparatively non-metaliic nature of arsenic and antimony. This 

 consideration leads us to suppose that the non-metals are still 

 more highly evolved than the metals, and that in the special di- 

 rection towards electro-negative polarity. Besides we know that 

 the intermediate links differ in degree, not in kind. 



The lessening of the atomic heat with increase of mass shows 

 a further absorption of motion, besides the potential energy pos- 

 sessed by the more massive atoms. It might be ob- 

 jected that motion has never been extracted from these 

 massive atoms ; on the contrary, as a rule, the heat of 

 combustion is greater as atoms of the element entering 

 into combustion are lighter. But the molecules of organic 

 matter must be decomposed by suitable means before they can 

 do any work ; just so with the elements, which receive their 

 name for the very re.ason that, as far as we know, they are in- 

 capable of decomposition. Perhaps, indeed, the increase in the 

 number of rays in the spectra of highly heated sulphur and nitro- 

 gen will be regarded as an instance of such motion. 

 , Thirdly, if we look at the atomic weight of groups of the ele- 

 ments, it is seen that the increase of mass occurs by a simple 

 proportion. Gladstone, Dumas, Odling and others have shown 

 the close relation of the numbers for particular groups ; whilst 

 lately Mendelejeff has given out a law of periodical recurrence, 

 connecting the properties and the atomic weight, either received 

 or theoretical, of all known elementary bodies. Thus we 

 have — 



Ca = 40 e 

 Ba = 137 ^"^ - 



iCl =35-5 Br 

 I = 127 ^^ 



Li 



40+137 _ SS-5 

 i (Sr=S7-5) 



- 35-5 + '27 - Si -25 



i (Br = 8i) 



7 Na _ 7 + 39'i _ 23'05 

 jK=30-i 2"~r(Na = 23) 



These instances suffice to show how near the calculated atonic 

 weights come to those found by experiment. 



In the fourth place it is a significant fact, that the elements 

 themselves become changed in properties under different circum- 

 stances ; the allotropic forms that result may be said to corre- 

 spond with "varieties " among organised bodies. In the case of 

 the elements greater atomic mass was said to denote evolution ; 

 in the best known allotropic varieties we find change from the 

 normal form to be accompanied by increased density. Thus 

 ozone (allotropic oxygen) and red phosphorus have both a greater 

 density than the usual forms of these bodies. 



With greater evolution, the so-called elements become more 

 electro-negative ; so in tliese instances, ozone has a greater 

 affinity for hydrogen and the metals than has oxygen, and amor- 

 phous phosphoras less affinity for oxygen than ordinary phos- 

 phorus. 



The varieties of sulphur would seem to be exceptions, for they 

 are of less density than the usual form ; the specific gravity of 

 ci^stallised sulphur is 2"05, that of plastic sulphur, i '95. However 

 Berthellot terms the crystallised octagonal variety, electro- 

 negative, plastic sulphur, on the contrary, electro-positive. Hence 

 the octagonal form is at once denser and more electro-negative, 

 and should be regarded accordingly as more highly evolved. 



In the fifth place, let us note some of the actions and re- 

 actions of matter and forces. 



(<;) Heat : In any organic group, generally speaking, the 

 greater the vapour density, accompanying greater complexity, 

 the higher is the boiling point. So it is with the elements, taken 

 according to natural groups, the greater the atomic weight, the 

 higher the fusing or boiling point. This is seen in the case of 

 chlorine, bromine, and iodine ; arsenic, antimony, and bismuth, 

 &c. Exceptions to this rule are the three closely allied metals, 

 zinc, cadmium, and mercury, the most volatile of which is the 

 heaviest, the least volatile, the lightest. Again, the more com- 

 plex the chemical constitution of bodies is, the worse, generally, 

 do they conduct heat and electricity : so too the more hit,'hly 

 evolved and massive the atoms, the worse conductors are they 

 as a rule. This applies strictly only to groups, as calcium con- 

 ducts better than barium or strontium, but silver, though heavier 

 and of greater atomic weight, nearly five times better thin 

 calcium. The difference of conducting power between metals 

 and non-metals is very apparent. Where the atomic mass is 

 greater, as the body verges more towards the electro-negative, this 

 loss of conductibility and the high fusing point is easily accounted 

 for by the mechanics of motion. The heavier atom takes longer 

 to communicate its motion in the one case ; or is more difficult 

 to move in the other. 



Some natural groups of the elements offer good examples of 

 what has just been stated, e.g. 



Hydrogen has the greatest conducting power of all gases. To 

 the principle that lighter atoms have greater polarity or chemical 

 affinity, Bunsen has found an exception, that cesium is heavier 

 and yet more electro-po-ilive than pot.assium or sodium. 



The order of solubility or of chemical activity shows that 

 chlorine and calcium are the more generalised of their respective 

 groups, as]we should expect. 



