734 
NATURE 
[JUNE 2, 1923 

clear that this element stands in a class by itself, and 
need not be forced into association either with the 
alkali metals or with the halogens. The final chapter, 
on atomic structure, is remarkable in that it begins 
with a recapitulation of some of the fantastic ideas 
of atomic structure that preceded the discovery of the 
electron, while it concludes by dismissing Bohr’s atom 
as “considerably overrated,” and setting up in its 
place ‘‘Stewart’s atom” as possessing merits which 
are not possessed by the atoms of other workers. 
The various chapters of the book do, however, 
provide useful summaries of work which must other- 
wise be studied either in separate monographs or in 
original literature, and to those who prefer this method 
of assimilating knowledge the book may be com- 
mended. 
(3) Prof. Smits, whose monograph on allotropy 
has been translated from the German, deals with a 
very interesting subject, namely, the application~ of 
the phase rule to those cases in which at least one of 
the components is capable of existing in more than 
one form, so that the familiar phenomena of phase- 
equilibrium are complicated by the occurrence of a 
reversible isomeric or polymeric change in this com- 
ponent. When the change is sufficiently rapid, the 
component in question counts as one molecular species ; 
but when the change is slow, each separate form must 
be treated as a separate species. 
There can be little doubt that if the editor of these 
text-books had entrusted to Prof. Findlay the work 
of expounding the application of the phase rule to 
these fascinating cases, he would have been able to 
tell the story in simple language, and in such a way as 
to interest and attract the type of student for whom 
these monographs are written. It is, however, certain 
that, while a translation of the monograph into English 
is a real advantage as eliminating one of the most 
formidable difficulties of the student, who usually 
finds German not an easy language to read, even the 
translation gives the impression that the author has 
deliberately made the subject as difficult as possible. 
One must assume that in his own teaching the author 
discusses these phenomena at the close of a rigorous 
course of training, and that those who have followed 
his lectures may perhaps find in the theory of allotropy 
a puzzle worthy of their highly developed skill; but 
to the student who has not gone through this training, 
no mercy whatever is shown, and he might well be 
excused for forming the opinion that Prof. Smits, 
like one of the old alchemists, was trying to disguise 
his knowledge, instead of to diffuse it, by using a 
bewildering system of symbols and diagrams. Almost 
any one of these might “hold up” the reader for 
many minutes, if not indeed for hours, while he was 
NO. 2796, VOL. I11] 

trying to discover what meaning he must attach to 
symbols decorated with a positive cascade of super- 
script and subscript signs, and thus to find out the 
inner meaning of the diagram. By way of further 
punishment, the author omits*to write down the 
chemical formule of the organic compounds with 
which he deals, so that the student must refer to the 
original literature if he wishes to know what formule 
have been assigned to the two forms of benzoyleamphor, 
or to the various modifications of milk sugar. In 
this case it would appear that the author is so con- 
cerned with the mathematical dissection of these 
compounds in their various phases that he has no 
interest whatever in their chemical composition ; and 
this view is supported by the attitude which he adopts 
in similar cases throughout the volume. 
In conclusion, it may be said that if a keen student 
wishes to test his abilities by means of a volume which 
might well bear the sub-title, ‘‘ The Phase Rule made 
Difficult,” the book might perhaps be commended. 
On the other hand, the average student will probably 
prefer to wait for an interpreter before he attempts 
to study the work of an author whose desire for com- 
plexity leads him to postulate the existence of half a 
dozen molecular species in the simple and orderly 
space-lattice of a metal. 
(4) Prof. Pauli’s monograph on the colloid chemistry 
of the proteins possesses nearly all the merits that are 
lacking in Prof. Smits’ book. Although dealing with 
a much more difficult subject, it has the merit of being 
not only brief, but also as simple as any treatise on 
colloids that has yet appeared. Not only those who 
are specially interested in colloid chemistry, but also 
chemical students generally, would find both pleasure 
and profit in’reading the book, and on these grounds 
it can be heartily commended. It is, indeed, a parti- 
cularly easy task to review a book on which none but 
favourable comments are possible. 
(5) Prof. Holmes, at the request of the Colloid 
Committee of the National Research Council, has 
written a “‘ Laboratory Manual of Colloid Chemistry.” 
The total number of experiments described in the 
book is 186, and most of these have been tested in 
the laboratory over a period of six years. It is an 
indication of the importance that now attaches to 
the study of colloids that a book dealing with laboratory 
experiments only should be called for, and Prof. 
Holmes has produced a volume which every teacher 
of physical chemistry will find it necessary to possess. 
It will also be welcomed by many other workers who 
are not responsible for the organisation of laboratory 
classes in physical chemistry. 
(6) Mr. Price has invented a tetrahedral model of 
the carbon atom which has an equilateral triangle 

; 
: 
