SEPTEMBER 21, 1916| 
from introduced species... Those who read the 
early reports by Dr. Perkins, of the British Asso- 
ciation Committee, will remember how rapidly 
the endemic insects were being replaced by 
foreigners which had been introduced accident- 
ally; this book deals with a further phase of that 
sad drama.’ We all know how successful the 
Americans of the United States have been in deal- 
ing with the problems of economic entomology, 
and in Hawaii this experience has proved most 
beneficial, for not only have the enemies of pests 
‘been acclimatised, but in the importation of 
insects to combat the spread of the injurious 
Lantana we have, we are told, “the first example 
in the world of the introduction of insects to pre- 
_ vent the spread of a plant.” If one more grumble 
may be permitted, we would like to express sur- 
prise that any scientific man should adopt the 
popular but erroneous spelling for coconut; but 
_ to avoid an unpleasant concluding sentence it may 
be pointed out that all through the book there are 
occasional references to the ethnological aspect 
_ of certain plants and animals which are of interest 
to the ethnologist. 
‘ 
COLLOID-CHEMISTRY. 
A Handbook of Colloid-Chemistry. The Recog- 
nition of Colloids, and their General Physico- 
chemical Properties. By Dr. Wolfgang 
Ostwald. Translated by Prof. M. H. Fischer. 
Pp. xii+278. (London: J. and A. Churchill.) 
Price 12s. 6d. net. 
_ is stated in the preface that this book -has 
passed through three large editions in Ger- 
many. Weare inclined to think that such success 
- was due more to the fact that it was first in the 
field as a general treatise upon a subject which 
was attracting widespread interest than to in- 
trinsic merit. The ideas especially of the general 
theoretical portion are superficial, and the writ- 
ing loose, words being mistaken for ideas. It is 
stated more than once, for instance, that the 
colloid state is independent of chemical composi- 
tion. Taken literally, the statement is merely 
foolish. How foolish two examples will suffice 
to show. Azomethane, one of the most remark- 
able of colloid substances, loses its colloidal 
properties if a single hydrogen atom of its com- 
plex molecule is replaced by a halogen. Gold, 
silver, and platinum readily form colloidal solutions 
in solvents which contain a replaceable hydrogen 
atom, while the hase metals form such solu- 
tions in  hydroxyl-containing solvents. The 
author, however, does not really mean what he 
says. His many pages on the subject show that 
the thesis he is actually defending is the quite 
harmless one that for every substance some other 
substance can probably be found with which it will 
form a colloidal mixture. 
d The colloidal state is, to use Bredig’s happy 
phrase, a microheterogeneous state of matter. It 
is the great merit of. Picton and Linder that they 
made this clear. Dr. Ostwald characterises the 
different parts as “phases,” 
NO. 2447, VOL. 98] 
“ 
and speaks of colloids | 
NATURE 
AZ. 
as Rone systems. This is an unfortunate use 
of the word “phase,” which Gibbs defined as a 
portion of matter ‘‘uniform throughout, not only 
in chemical composition, but also in its physical 
state.” Probably the last thing we can. claim for 
portions of matter of microscopic, and especially 
ultramicroscopic, dimensions is that they are 
physically homogeneous throughout. The misuse 
of the word “component” on p. 36, where it is 
confused with “‘phase,’’ is probably an error of 
translation. 
The least satisfactory part of the book is the 
section on surface energy. Here the author, by a 
series of unsound analogies, introduces _unneces- 
sary confusion in a region which Gibbs, Rayleigh, 
and van der Waals had reduced to order. The 
part dealing with special properties of colloidal 
solutions, such as molecular weight, viscosity, 
osmotic pressure, etc., gives, on the whole, a clear 
account of the work which has been done. 
OUR BOOKSHELF, 
The Practical Principles of Plain Photo-micro- 
graphy. By George West. Pp. xii+145 
+plates villi. (Dundee: University College, 
George West, 1916.) Price 4s. 6d. net. 
Ix this book plain and practical directions are 
given for the preparation of photo-micrographs 
with the use of powers up to a }-inch objective. 
The author very rightly insists that the beginner 
should commence with low powers, and as he 
gains experience proceed step by step to the use 
of the higher powers. A feature of the book is 
its “common sense’’: the tyro is not bewildered 
by a mass of details and scores of chemicals and 
solutions, but just a few are chosen and fully 
described which the author has used and found 
suitable, and throughout directions are given for 
the adaptation of simple apparatus to the end in 
view. 
After a few pages of general introduction the 
subjects of microscope and powers, illuminants, 
colour screens and camera are dealt: with; then 
follow sections on photo-micrography with a land- 
scape camera, without a camera, and with a ver- 
tical camera. Next the details of the making of a 
photo-micrograph from beginning to end are 
given in dialogue form in the Sandford and 
Merton style, a method of instruction which per- 
sonally we do not care for, but which enables the 
author to give many “tips.” 
The book is illustrated with two plates showing 
arrangement of apparatys and six other plates, 
each with two figures, reproductions of photo- 
micrographs of various objects. These are 
described in the text, and a very full table is given 
of all the details respecting them—nature of the 
object and its staining, lens, illuminant, screen, 
plate, exposure, developer, etc. These should be 
very useful, giving the beginner just the informa- 
tion he wants. Finally, lists of necessaries, photo- 
graphic formule, books on photo-micrography 
(which might have been priced with advantage), 
and an index complete the book. 
