1876.] Recent Chemical Researches . 39 
that the elements of the nitrogen group are really penta- 
valent. 
Exceedingly interesting results are certain to followfrom re- 
searches into the total affinity force exercised by the elements 
as distinguished from their chemical valency. Hitherto this 
field of enquiry has had but few cultivators, probably on 
account of the difficulties which beset the problems pre- 
sented. A step in advance has been made by Wright, who 
has calculated the affinity of the elements, in several com- 
pounds, in terms of the heat gained or lost during the 
formation of the compound from its constituent elements ; 
but as Wright’s determinations have a more immediate 
bearing upon the questions to be considered when speaking 
of compound bodies, we shall defer a more detailed account 
of them to a later part of this paper. 
It is well known that several of the elements can exist in 
various so-called allotropic forms : these forms seem to be 
connedted with the original form of the element in some- 
what the same way as isomeric compounds are connected 
with the primary forms from which they are derived. 
We have already seen how Lockyer’s spedtrum researches 
lead to the idea that the molecules of the non-metallic 
elements are possessed of a large amount of plasticity : the 
fadts noticed in the study of the chemical history of these 
molecules fully confirm this theoretical dedudtion. If oxygen 
be subjedted to the adtion of the silent discharge it exhibits 
many new properties, yet we know that from the substance 
thus formed, oxygen — and oxygen only — can be obtained. 
We are obliged, therefore, to imagine that a change has 
taken place in some way in the inner strudture of the oxygen 
molecule, or that under the altered circumstances that mole- 
cule is endowed with different potential energy from that which 
it formerly possessed. The formation of one or other of these 
molecules is conditioned by the temperature ; at a tempera- 
ture of 300° C. ozone is decomposed with the formation of 
common oxygen. As the general adtion of heat is to cause 
greater freedom of molecular motion, we may perhaps con- 
clude that the atoms in the molecule of oxygen are possessed 
of a greater freedom of motion than those in the molecule 
of ozone. So, also, we know that if ordinary phosphorus 
be heated to a certain point, in an atmosphere incapable of 
adting upon it chemically, amorphous phosphorus is pro- 
duced ; but if the temperature be increased the produdtion 
of amorphous phosphorus ceases, and that which is formed 
is re-transformed into the ordinary variety. This adtion is 
clearly conditioned by the temperature, and therefore by the 
