22, 
NATURE 
(May 2, Tone 
to every chemist, student, and expert alike, for 
it should go far to dispel that somewhat doubtful 
confidence which the author quite rightly com- 
plains is still felt by the pure chemist as regards 
this important and fascinating branch of science. 
BiG. ©. Bauye 
THE CONSTITUTION OF THE SILICATES. 
Die Silicate in chemischer und _ technischer 
Beziehung: unter Zugrundelegung der seitens 
der philosophischen Fakultit der Universitat 
Géttingen preisgekrénten Hexitpentit - Theorie 
nebst Umwandlung derselben in eine allgemeine 
stereochemische Theorie. By Dr. W. Asch and 
Dr. D. Asch. Pp. xv+4o9. (Berlin: Julius 
Springer, 1911.) Price 16 marks. 
HE present work, which is an expansion of 
ol an essay originally submitted for a prize 
offered by the philosophical faculty of Géttingen, 
is a bold and original attempt to grapple with the 
difficult problem of the chemistry of the silicates 
and related compounds. The authors have sought 
to give a structural explanation of the behaviour 
of such compounds consistent with the doctrine of 
valency. ‘The “ Hexite-Pentite ”’ hypothesis, which 
forms the basis of the work, assumes that silicates 
and alumino-silicates are not, in general, derived 
from the simpler hydroxides, such as Si(OH), and 
Al(OH),;, but from compounds formed by the con- 
densation of six such molecules, with elimination 
of water, to form a closed ring. Less frequently, 
five-membered rings may be produced, and com- 
plex molecules are built up by the union, according 
to certain definite principles, of two or more such 
“hexite” or “pentite” groups. By the replace- 
ment of hydroxylic hydrogen by metals, of 
hydroxyl by fluorine, &c., formule are constructed 
which are capable of expressing with remarkable 
completeness the properties and reactions of many 
silicates and aluminosilicates. 
The formule, especially in the contracted nota- 
tion chiefly employed in the text, strongly recall 
the Kekulé theory of aromatic carbon compounds, 
but the analogy is not a real one, as the linking is | 
never from silicon to silicon or aluminium, but 
always through an intervening oxygen atom. 
Praise is due to the authors for the ingenuity with | 
which the hypothesis is applied, and for the labour 
expended in recalculating the enormous number of 
analyses given, and expressing them in terms of 
the new structural theory. A certain arbitrariness 
in the choice of many of the formule is unavoid- 
able, in the absence of experimental investigations 
specially designed to test the points in question. 
The most serious defect of the work is its 
disregard of physical considerations, owing to the 
NO. 2218, VOL. 89] 
‘affording assistance in the further 
exclusively chemical viewpoint adopted. This one- 
sidedness is well seen in the lengthy and detailed 
treatment of Portland cement and blast-furnace 
slag. Definite hexite-pentite formule are assigned 
to a great variety of these artificial products on 
the evidence of ultimate analyses only, and the 
that 
microscopical proof such materials are 
heterogeneous is brushed aside in a_ single 
sentence. Thermal analysis, by means of which 
such great advances are being made, including the 
brilliant work of the Geophysical Laboratory in 
Washington, is not considered, and the names 
of Day, Shepherd, and their collaborators do not 
even appear in the bibliography, although this 
includes some 1500 references. Again, the great 
additions made in recent years to our knowledge 
of colloids and of the part played by them in the 
chemistry of silicates are passed over in silence or 
with a brief allusion, in spite of the intimate 
bearing of such work on the weathering of 
felspars, the setting of cements, the hydration of 
zeolites, and similar questions, all of which are 
discussed from a purely structural point of view. 
Even to glasses and porcelain definite structural 
formulz are assigned. 
By replacing silicon and aluminium atoms by 
other elements, and by introducing stereochemical 
considerations, the hypothesis is extended to com- 
plex salts, metal-ammonia compounds, and salts 
with water of crystallisation. Some shorter 
chapters are devoted to further and more hazard- 
ous speculations, the hexite-pentite arrangement 
being applied to aliphatic organic compounds, and 
even to the structure of the atom and the explana- 
tion of radioactivity. These extravagances, how- 
ever, do not detract from the value of the main 
thesis, which certainly deserves the attention of 
inorganic chemists and mineralogists, as possibly 
study of a 
C. H. Descu. 
complex and difficult subject. 
BRITISH VEGETATION. 
Types of British Vegetation. By members of the 
Central Committee for the Survey and Study of 
British Vegetation, Edited by A. G. Tansley. 
Pp. xx+416+36 plates. (Cambridge: Univer- 
sity Press, 1911.) Price 6s. net. 
HE great impetus that has been given during 
“E recent years to the study of the British flora 
is largely owing to the development of that branch 
of botany known as ecology. This subject—the 
study of plants in connection with their habitat— 
has raised many questions, and amongst them 
that of plant-communities has received foremost 
attention, and has been zealously investigated. 
The committee which was formed in 1904 to 
