400 J. P. Cooke on the Numerical Relation 
The Five Series is the shortest of all, consisting of only three 
members, carbon, boron and silicon. Of these, the last two are 
as closely allied as are any two members of the other series, sili- 
con having precisely the properties we should expect in a homo- 
logue of boron, which was lower in the series; and the same is 
also true of their compounds. The analogies, however, between 
these two elements and carbon are by no means so close, for not 
only carbon cannot be proved to be isomorphous with them, but 
it does not form similar compounds. Carbonic acid, it is true, 
presents some points of resemblance to boracic and silicic acid; 
like them it unites in a large variety of proportions with bases, 
its alkaline salts give a basic reaction, &c. ; but according to the 
generally received opinion, its symbol is COz, while those of bo- 
ron and silicon are BOs and SiOs. In its uncombined state, 
however, carbon resembles boron and silicon, not only in its out- 
ward properties, but also in its action before the blowpipe. “I'wo 
of the allotropic states of carbon, graphite and charcoal, are prob- 
ably repeated in boron, and are known to be insilicon. ‘The 
principle of exclusion would also seem to place carbon in this se- 
ries, for it certainly presents no analogies with the members of 
any other. The correspondence of the atomic weights of the 
members of this series to the law is remarkably close. 
ble, or nearly insoluble, in water. And finally, the elements of 
the series have all those physical properties which are known 4s 
metallic properties, 
This series may be naturally divided into two sub-series. The 
first contains those elements whose protoxyd bases are their chat- 
acteristic compounds, and which do not form acids with oxyge)- 
e second contains those elements whose characteristic com- 
pounds are their sesquibases. They generally unite with two OF 
more equivalents of oxygen, and form acids. These sub-series 
are distinguished in the table in the same way as those of ‘the 
Six Series. Corresponding to these sub-series we have two sets 
