1877O Chemistry of the Future. 305 
Thus if we recur to the four series above mentioned : — 
No. 4 . 
. K 
Ca — 
Ti 
V 
Cr 
Mn 
No. 5 . 
. Cu 
Zn — 
■ — 
As 
Se 
Br 
No. 6 . 
. Rb 
Sr — 
Zr 
Nb 
Mo 
— 
No. 7 . 
• Ag 
Cd In 
Sn 
Sb 
Te 
I 
Here it is at once evident that there a decided analogy 
prevails between the corresponding members of Nos. 4 
and 6, and again of Nos. 5 and 7. But between Nos. 
4 and 5, 5 and 6, or 6 and 7, there is no such analogy. 
Table II. shows the elements as arranged in “great 
series.” In Series I. stands hydrogen alone. This reminds 
us of a remark made lately by Prof. F. Guthrie, that very 
generally the commonest bodies are the most anomalous. 
Series II. contains the seven elements from lithium to 
fluorine inclusive, these two first groups being designated 
“typical.” Series III. contains also seven elements. 
Series IV. contains fourteen bodies, which, when the three 
blanks indicated by M. Mendeleeff have been filled up, as 
one of them already is by the discovery of gallium (eka- 
aluminium), will be raised to seventeen. 
This “ great series ” consists of the two “ small series,” 
No. 4 and No. 5, with three of the non-serial elements — 
iron, cobalt, and nickel — interposed between them. The 
great series No. 5 is composed of sixteen known elements, 
and a blank space is left for a body not yet discovered. 
The small series here embraced are Nos. 6 and 7, and 
again three of the non-serial elements — -ruthenium, rhodium, 
and palladium— are interpolated. The great series VI. is 
very imperfect, comprehending only four elements, which 
are placed parallel with the first four bodies in Nos. IV. 
and V. Great series VII. is more perfect ; it contains 
parts of two small series, and again three non-serial ele- 
ments — osmium, indium, and platinum. Here, however, 
we are struck with a difficulty : between the atomic weights 
of tungsten (W = i 84) and osmium (Os = 195) there is the 
gap of 11. Now if M. Mendeleeff concluded that two un- 
discovered elements, eka-aluminium and eka-silicium, must 
exist to fill up the interval of 10 between Zn = 65 and 
As = 75, in great series IV., why may we not with equal 
right calculate on the discovery here also of two unknown 
bodies ? But should this be hereafter found to be the fadt, 
the correspondence between the members of Series V. and 
VII. will be deranged. Gold will occupy the position 
corresponding not with silver, but with cadmium ; mercury 
VOL. vii. (n.s.) y 
