between the Atomic Weights. 391 
the acids become less and less volatile, less and less fluid, less and 
less corrosive; first oily, then fat-like, and finally hard, brittle 
solids, like wax. As is well known, the composition of these 
acids varies in the same way, and the variation follows a regular 
law, so that by means of a general symbol we can express the 
composition of the class. ‘This symbol for the volatile acids may 
be written (C2H)Os, HO+n(C:H:2). 
This description of the well-known series of the volatile acids, 
applies, word for word, nominibus mutatis, to each of the six 
series of chemical elements. The elements of any one series 
form similar compounds and produce similar reactions ; moreover, 
they resemble each other in another respect in which the mem- 
bers of the organic series do not. Their crystalline forms are 
the same, or, in other words, they are isomorphous. Although 
this may be true of the volatile acids, yet it cannot be proved in 
the present state of our knowledge. Still further, many of their 
properties vary in a regular manuer as we descend in the series. 
be expressed algebraically, though in most instances it cannot be 
determined. Finally, as one general symbol will express the 
composition of a whole organic series, so a simple algebraic form- 
ula will express the atomic weight, or, if you may please so to 
term it, the constitution of a series of elements. _ 
ints may be illustrated with any of the series in the 
table; with the first, for example, which consists of oxygen, 
fluorine, cyanogen, chlorine, bromine, and iodine. All these ele- 
ments form similar compounds, as will be seen by inspecting the 
symbols of their compounds given at the right hand of the list of 
names, where the similar or homologous compounds are arranged 
in upright columns. Moreover, they are all isomorphous, as ma 
seen by referring to the left-hand side of the list, where the 
similar compounds in each upright series are jsomorphous, the 
humbers at the heads of the columns indicating the systems 0 
Bromine is a fluid at the ordinary temperature ; aud, finally, iodine 
is a solid. Moreover, starting from cyanogen, the solubility of 
ences between the atomic weights of these elements are always 
4 multiple of nine. This general formula may be said to repre- 
