CHEMICAL SCIENCE. 



281 



Differences. 



Calculated equivalents. 



Received equivalents. 



44 . . 

 44 . . 

 44 



. . . . Hg = 100 

 . . . . Cd = 56 



. . . . Mg = 12 



Zn = 36-2 



The salts of the protoxides of the three last of these metals are isomor- 

 phous, and the metals themselves are all volatile. 



It is not a little curious that the numerically negative members of this 

 series lead into the positive members of the foregoing. If we continue the 

 subtraction of 4-1, we find for the fifth number 76, or nearly the equivalent for 

 arsenic; for the sixth 120, very nearly that of antimony; for the seventh 164, 

 corresponding, as before remarked, with a possible undiscovered metal; and 

 for the eighth '208, or exactly the equivalent of bismuth. The two series 

 thus naturally lead to each other. 



The members of these two analogous series are further united by the fact 

 that all of them, eleven in number, are capable of uniting with the hydro- 

 carbons of the methyl, ethyl, etc., type to form powerful organic metals, 

 and that this capacity appears to be limited to these elements alone. 



The magnesia group includes a well-marked natural family of metals, 

 whose oxides having the constitution RO are related with each other by 

 isomorphism. The equivalents of these metals, according to the most 

 recent determinations, are as follows : 



Magnesium, 12 



Manganese, 27 5 



Iron, 28 



Cobalt, 29-5 



Nickel, 29-6 



Uranium, 60 



Chromium, 26'7 



Zinc, 32-6 



Cadmium, 56- 



Copper, 31-7 



Lead, 103-5 



They are furthermore related in the following manner by 44 : 



Thus, with Cu and Mg, Zn and Mg, the sum of each pair is 44 nearly. 



With Cd and Mg, Pb and Ur, the difference of each pair is 44 or nearly. 



With U and Mg, U and Fe, U and Co, U and Ni, U and Cr, Cd and Zn, 

 the mean term is 44 or nearly. 



With Pb and Mn, Pb and Fe, Pb and Ni, Pb and Co, Pb and Cr, the sum 

 of each pair is three times 44 nearly. 



The strong analogy existing between Mg, Cd and Zn, extends to their 

 equivalents, that of Mg being added to that of Zn gives the number of 44 

 nearly, subtracted from that of Cd, 44 exactly. 



Mr. Lea also shoAvs, in a like manner, that relations depending upon the 

 number 44, exist between the equivalents of the following metals, which 

 maybe classed together as tending to form acids; viz., tin, titanium, tant- 

 alum, tungsten, vanadiam, molybedenum, tellurium, niobium. 



If commencing with gold, Au == 197, we form a diminishing series with a 

 common difference of 44'5, we shall find for its terms 



24* 



