Haughton — The Atomic Weights of the Chemical Elements. 91 
At the commencement of the year ]875 there were three unknown 
elements of this Table, viz. : — 
Gallium, found in 1875 ; 
Scandium, found in 1879 ; 
Germanium, found in 1886. 
And it is the glory of the Periodic Law of Modern Chemistry that 
it predicted (approximately) the atomic weights of these three un- 
known elements and their valencies, which predictions were fulfilled 
by the successive discovery of the unknown elements. 
In Plate vii., which is a representation of the third and fourth 
periods of Dr. Eeynolds' curve, we can see that a triad element is 
wanting between calcium and titanium, and both a triad and tetrad 
element wanting between zinc and arsenic. These missing elements 
were predicted and found. 
It is quite true that there were three well-known elements lying 
between manganese and copper, viz. iron, nickel, and cobalt ; but 
these three elements did not conform to the rules of the Periodic Law, 
and their places have been taken in that law by scandium, gallium, 
and germanium. 
They were like the ''three children in the oven" described by 
Daniel (Shadrach, Meshach, and Abednego), who refused to worship 
the Golden Image or Periodic Law set up by JN^ebuchadnezzar and the 
modern chemists. 
I hope to show in the present Paper that iron, nickel, and cobalt 
are not so refractory as they appear at first sight ; but, on the con- 
trary, ready to take their proper places on the chemical curve when 
rightly interpreted. 
An inspection of Plate vii. shows (just as we found in the former 
curve in the case of the tetrad elements, carbon and silicon) that the 
line joining the tetrad elements, titanium and germanium, contains five 
elements, viz. : 
Ti I Ya I Ca I Ga I Ge, 
leaving nine elements free, which sit upon a general cubic — 
K I Ca I Sc I Cr I Mn I Zn I As I Se I Br. 
