
AuGUST 12, 1915] 
NATURE 
641 


cation, these measurements afford results of con- 
siderable interest, and according to the writer’s 
experience the transition-point method is capable 
of the same degree of accuracy as the familiar 
method of freezing-point depression. | Notwith- 
standing small deficiencies of this nature, the book 
must be ranked as a valuable contribution to the 
series of monographs on selected chapters of 
physical chemistry. Inka WED} 
THE FUNDAMENTALS OF THREE-COLOUR 
PHOTOGRAPHY. 
Three-Colour Photography: with Special Reference 
to Three-Colour Printing and Similar Processes. 
By Arthur Freiherrn von Hiibl. Translated by 
H. O. Klein. Pp. 138. (London: Percy Lund, 
Humphries and Co., Ltd., 1915.) Price 7s. 6d. 
HE scope of this volume is much more 
limited than the title might be supposed 
to indicate. The author deals with the theories 
of light and colour so far as concerns the subject, 
and in a thoroughly practical way with the sen- 
sitising of plates, the making and choice of colour 
filters, and, the choice of inks, but the actual 
printing processes themselves are barely men- 
tioned. Screen-plate processes, such as the use 
of autochrome and similar plates, are not dealt 
with. We have therefore a treatise on the funda- 
mentals of three-colour photography. We must 
first express our disappointments. At page 95 there 
are eight absorption spectra, showing the effect 
of each dye in two concentrations, but we cannot 
find any indication as to the dyes to which these 
spectra refer. There are references to ‘“‘ Supple- 
ment IV.,” a coloured plate which should contain 
some most interesting results, but the plate is not 
anywhere to be found. At page 80 we are told 
that “for accurate work it is necessary to measure 
the densities with the aid of Marten’s polarisation 
photometer,” as if this were the only instrument 
suitable for this purpose, or the only accurate 
photometer applicable. Of course, there are many 
forms of photometer available, and not everyone 
would prefer the Marten instrument. 
Having said so much, we have nothing to 
express but a vivid appreciation of the value of 
the treatise. The formule given are not in- 
numerable, but they are the select few chosen 
by one who is thoroughly conversant with the 
subject. It is interesting to note that the author 
is not one who struggles after theoretical perfec- 
tion at any price, as some seem to do, perhaps 
because of their want of acquaintance, with the 
practical side of the art. He says quite clearly 
that three-colour photography is based upon sound 
theoretical principles, and fully justified from a 
theoretical standpoint. But on the other hand, 
NO. 2389, VOL. 95] 


it is more or less immaterial whether or not the 
photographic colour analysis is absolutely correct, 
and that “fine-etching or retouching is the 
greatest factor in solving the problem of three- 
colour process work.” One may be rather sorry 
to see so high an authority take up such a posi- 
tion, but he justifies his opinion with regard to 
inks, by pointing out that the theoretical inks are 
so “very bright and fiery,” that the colour scheme 
is very sensitive, and therefore the slightest error 
in the balance of the pigments makes it impossible 
to produce neutral greys or black under ordinary 
printing conditions. The use of a pure yellow, 
an almost blackish blue, and a very deep red 
allows of slight variations in their proportional 
intensities without greatly influencing the result, 
and are to be preferred, although they reduce, to 
a certain extent, the range of colours that can be 
reproduced. Moreover, artists use blackish (not 
pure) colours, and the “colour magnificence of a 
painting is not due to the use of brilliant pig- 
ments, but to the effects of colour contrast.”” The 
pigments of modified colour have the further 
advantage of being less liable to change on ex- 
posure than those that more nearly approach the 
theoretical requirements. In spite of this apparent 
qualification of the indications of theory pure and 
simple, the theory is and remains sound, and it 
is only the uncertainties of practical work that 
require a little concession. Cay: 

MEDICINES AND THEIR MANIPULATION. 
(1) The Extra Pharmacopeia of Martindale and 
Westcott. Revised by Dr. W. H. Martindale 
and W. W. Westcott. Sixteenth Edition. 
Voli Pp, xl--nur3gs)) Price 14's. net... Violets 
Pp. vili+469. Price 7s. net. (London: H. K. 
Lewis, 1915.) 
(2) Squire’s Pocket Companion to the British 
Pharmacopeia. By P. W. Squire. Second 
edition. (London: J. and A. Churchill, 1915.) 
Price tos. 6d. net. 
(rt) HE first volume of Martindale and West- 
cott’s Extra Pharmacopeeia contains all 
matters relating to the chemical and therapeutic 
properties of those  ‘‘extra-pharmacopceial” 
chemicals and drugs which have attracted particular 
attention in the medical world. It includes details 
of their manufacture and modes of administration, 
their medicinal uses, pharmacy and _ solubilities, 
and references to current literature. This volume 
also contains, inter alia, a chapter on vaccines, 
supplying much new information, the section on 
organo-therapy, the supplementary list of drugs, 
and a list of the most potent antiseptics based on 
researches by the authors. Volume ii. contains 
the latest methods of assaying and _ testing 
