1 877.] The Chemistry of the Future . 299 
elements stand in a simple regular ratio to each other. 
Thus in the calcium group, taking the old atomic weights, 
we find a progressive increase of approximately 24, the 
other properties undergoing a correspondingly progressive 
change. In the sulphur group — sulphur, selenium, and tel- 
lurium — -the increase of atomic weight on the present scale 
is approximately 47, with again a progressive modification 
of properties. Similar developments, which need not here 
be particularised, have been demonstrated in the potassium, 
the chlorine, and the phosphorus groups. It has also been 
noticed, if we are not mistaken, that — although no definite 
ratio be discoverable — -the atomic weights of all the common 
elements are low, and those of the rarer high. It appears, 
further, that only the elements of low atomic weight enter 
into the composition of organised beings. With the very 
limited exception of copper (Cu = 63) found in the chocolate 
nut, in the blood of certain crustaceans, and in the feathers 
of the touraco, and of zinc (Zn = 65) in the ash of a pansy, 
iron (Fe = 56) has the highest atomic weight of the organic 
elements.* Again, the elements with high atomic weights, 
beginning with vanadium (V = 5i) and chromium (0 = 52), 
with perhaps the single exceptions of manganese and iron, 
may be regarded as poisonous whenever they exist in a 
soluble condition. But although such generalisations have 
not been wanting, there has been no attempt at bringing all 
the apparently independent groups into harmonious connec- 
tion. M. Mendeleeff considers that the regular dependence 
of the properties on changes of the atomic weight appears 
most clearly on the consideration of dissimilar elements, by 
the study of which he was led, in 1869, to the discovery of 
his <c periodic law.” This law he expressed in the following 
words : — “ The properties of simple bodies, the constitution 
of their combinations, as well as the properties of the latter, 
are periodic functions of the atomic weights of the elements.” 
There is one term here so generally misunderstood and mis- 
applied, not merely by persons of good general education, 
but even by scientific writers, that the meaning of M. Men- 
deleeff’s law will scarcely be understood at first sight. The 
word “ period ” is commonly used to signify any portion of 
* It may be said that we are using the term “ organic element,” or “ organ- 
ogen,” in a manner different from its usual acceptation. We are perfectly 
aware of this difference; but we submit that every element really assimilated 
by plant or animal, and not merely lodged in its tissues as a foreign and hos- 
tile intruder, — e.g., mercury in the bones of a votary of blue pill and calomel 
— has the right to be considered an “ organogen.” Lead (Pb = 2oy) has been 
found in the metallic state in the intestinal canal of irsedts but there is no 
evidence whatever in support 0 its assimilation. 
