ee LL - —_ e eSTLUrrh rlrll 
JANUARY I, 1914] 
NATURE 
499 
Cohen’s by saying that whilst the former 
was largely an accumulation of facts, the 
latter is chiefly an exposition of theories and 
principles. There is much less recital and much 
more discussion. The mechanism of the chemical 
reaction, rather than the properties of the product, 
is now insisted on; and rightly so, for this aspect 
of the matter is the more philosophically interest- 
ing and scientifically valuable. 
In the first chapter, dealing with the valency 
of carbon, we come at once into a region where 
speculation and discussion are rife. The author 
explains the chief theories which have been pro- 
pounded to account for the existence of bivalent 
and tervalent carbon, unsaturated groups, labile 
forms, and so on. He then passes to the con- 
sideration of the nature of organic reactions, 
including such processes as the addition of ele- 
ments or groups to unsaturated compounds, 
autoxidation, catalytic reduction and oxidation, 
condensation, and the formation of chains and 
rings. The portions dealing respectively with 
Thiele’s theory of partial valencies and with con- 
densation processes will be found especially useful. 
Indeed, these first two chapters of the work, with 
their references, might well have served as the 
basis for the address of the president of Section 
B at the recent meeting of the British Association. 
In chapter iii. we have an exposition of the 
dynamics of organic reactions. It is satisfactory 
to note that many of the examples are drawn 
from the Transactions of the Chemical Society of 
London—as indeed is the case throughout the book. 
Molecular volume, refractivity, dispersivity, 
magnetic rotation, thermochemistry, and absorp- 
tion-spectra are next dealt with, and the results 
applied to problems of molecular architecture. An 
interesting discussion of the relations between 
colour and structure follows, and the book ends 
with an account of the photochemistry of organic 
compounds. 
Occasionally it is not too clear which of two 
or more theories the author adopts, or favours; 
but a student who masters the substance of this 
and the companion volume will be justified in 
considering himself well grounded. 
(2) The first edition of this work has been 
favourably known for several years to chemists 
and others concerned with essential oils. To use 
the translator’s phrase, it was “a happy blending 
of history with chemical science and technology ” ; 
and this characteristic is maintained in the new 
edition. Two volumes, however, are now re- 
quired, the one under review containing (inter 
alia) the historical matter. This has received 
additions here and there, but remains substantially 
NO. 2305, VOL. 92] 
; of Anglo-Saxon conquest 
development of the trade in spices and aromatics 
during the Middle Ages, and trace the general 
history of the volatile oils—the essential principles 
of most spices and aromatic plants—from early 
Egyptian times onwards. Following this are sec- 
tions giving the history of the individual volatile 
oils and of distillation processes. The whole 
forms an interesting and valuable monograph, 
enriched with numerous references and quota- 
tions; the sketches of ancient distilling apparatus 
and the photographs of their modern successors 
are worthy of note for the contrast they offer. 
Distillation is a subject closely connected with 
that of volatile oils, since these are usually ob- 
tained by distilling the oil-bearing plants with 
steam. Not always, however; in certain cases 
heat destroys the delicacy of the perfume, or the 
| oil does not separate from the condensed water. 
In such instances the oil is either extracted direct 
| from the flowers with a volatile solvent such as 
petroleum ether, or absorbed by a suitable fat 
(enfleurage: maceration). These: processes are 
described by the authors in the next chapter, after 
which the general chemical constituents of the oils 
are dealt with. The chapter describing these is 
the longest and most important in the book. All 
necessary information appears to be given, in- 
cluding numerous structural formule, and lists of 
the plants in which each constituent has been found. 
Finally, there is an account of the general 
physical and chemical methods used in the assay 
of volatile oils, with notes on adulterants, and 
two useful analytical tables. The characters of 
thé individual oils are not dealt with in the present 
volume, but the new edition of ‘“ Gildemeister ” 
promises to be the best work on volatile oils which 
has yet appeared in English. C. S: 
OUR BOOKSHELF. 
Early ‘lars of Wessex: Being Studies from 
England’s School of Arms in the West. By 
A. F. Major. Edited by the late Chas. W. 
Whistler. Pp. xvi+238. (Cambridge: Uni- 
versity Press, 1913.) Price ros. 6d. net. 
“Wessex had to face a determined enemy, which 
was the most important factor in her steady rise 
to power” (p. 87). ‘‘The western Wessex fron- 
| tier was for two centuries practically the school 
of arms for England” (p. 91). After the wedge 
was driven to the 
Severn by the battle of Deorham in 577, 
separating the Welsh of the Cornish peninsula 
from their kindred, the Welsh kingdom of 
Dyvnaint (Dumnonia) kept its independence for 
two centuries. The Cornish kingdom held out 
for another century. It was the Welsh that kept 
this famous “school of arms” going, and it took 
| Wessex some 350 years altogether to learn its 
as when first published. The authors outline the | lessons (p. 83). 
