186 
NATURE 
TAPRiL, 23,0104 
the present volume contains many _ polemical 
replies, notably in connection with the constitu- 
tion and hardening of Portland cements. These 
hydraulic cements are considered to be basic lime 
salts of complex aluminosilicic acids containing 
coalesced hexite and pentite rings with calcium 
oxide side-chains replacing the hydroxyls of the 
hydrated silicon complexes, and occasionally con- 
taining alkali metals similarly attached to the 
aluminium hexite ring's. 
It is highly probable that the refractory oxides, 
silica, alumina, and their allies exist in highly com- 
plex molecules, and since among both inorganic and 
organic compounds there exists a certain tendency 
for the formation of five- and six-membered rings, 
it would probably be accepted by most chemists 
as a working hypothesis that such cyclic systems 
occur in the natural and artificial aluminosilicates 
and their derivatives, but it is open to doubt 
whether the authors do not greatly prejudice their 
case by attempting to extend this hypothesis to 
the explanation of the facts of coordination, 
radioactivity, and the constitution of organic sub- 
stances, such as benzene, the artificial colouring 
matters, and the proteins. 
(5) The appearance of this volume is a welcome 
indication that this monumental treatise on inor- 
ganic chemistry will be brought to completion in 
spite of the untimely death of its originator, the 
late Prof. Richard Abegg. There still remain 
for consideration, however, several important 
groups of elements, and the remaining volumes 
of the work are eagerly awaited by all interested 
in the systematic study of the chemical elements. 
A praiseworthy feature of the treatise so far as 
it has yet appeared is the thoroughness with which 
the compilers have accepted the periodic classi- 
fication of the elements; this insures uniformity 
of arrangement, and renders the task of reference 
a very easy one. It is rarely necessary to turn 
to the indexes. The present volume is devoted 
to the halogens and manganese, the elements of 
the seventh periodic group. In the case of each 
element the opening section deals with the deter- 
mination of its atomic weight. The descriptions 
of the physical and chemical properties of the 
elements and their compounds are very complete, 
and include, in addition, the mathematical treat- 
ment of many important examples of chemical 
equilibria, such as the Deacon’s chlorine process, 
the variations in the vapour density of the halo- 
gens and their partition coefficients in various 
solvents. Special sections deal with the colloidal 
chemistry of the halogens and manganese. 
The bibliography is remarkably full, there being 
more than fifteen hundred references for iodine 
N@I628 2 cv OL. O32 | 
and its derivatives alone. Manganese varies con- 
siderably in its habit of combination, and _ its 
compounds are arranged whenever possible under 
the headings of the various valencies of the metal, 
but reference is also made to its alloys, and to 
compounds in which the valency of the metal is 
undetermined. Geiss 
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