594 
NATURE 
[APRIL 14, 1904 
would be necessarily existing in the normal carbide 
condition. 
Turning to the vexed question of nomenclature, the 
chapter on what M. Osmond calls the distinct con- 
stituent ‘‘ sorbite ’? will hardly convince those who re- 
gard this substance as merely the first of three phases 
of pearlite. On p. 87 the author says, concerning 
sorbite :-— 
““ Often very fine and deep lamella of cementite are 
found which are more or less continuous: this is what 
Fig. 45 (polish-attack vx 1500) ought to show, if the 
feebleness of the original photograph has _ been 
sufficiently reproduced, which is doubtful.’’ 
The reviewer does not pretend to grasp the mean- 
ing of this paragraph, unless owing to faulty trans- 
lation the word feebleness has been substituted for 
delicacy. The following lines on p. g1 are also 
obscure; referring to sorbite M. Osmond says :— 
“Tn the first edition of this work I did not give 
with sufficient clearness, ideas which were perhaps 
slightly confused.”’ 
cc 
With reference to ‘‘ martensite,’? which M. Osmond 
calls ‘“‘the fourth constituent,’?’ many metallurgists 
hold that it is a crystalline structure found in both 
hardened and unhardened steels, and hence cannot be 
a constituent. 
It is stated by Mr. Stead in his preface that the 
special appendix on what M. Osmond calls the con- 
stituent ‘* austenite ’’ renders the work complete. On 
p. 39, Fig. 20, is figured in an excellent photomicro- 
graph a pale substance stated to be austenite, and a 
dark substance which is called martensite. Carbonists, 
however, hold that the pale areas are hardenite con- 
taining dissolved cementite, the dark areas being a 
mixture of hardenite and free cementite (M. Osmond’s 
methods are evidently not sufficiently delicate to detect 
in the dark so-called martensite the constituent last 
named). On etching, the hardenite with the free 
cementite assumes the anode position, but the areas of 
hardenite with the dissolved cementite assume the 
kathode position, and are hence unacted upon. 
In the appendix on “ austenite,’? a 1.55 per cent. 
carbon steel was evidently annealed in iron ore until 
the surface carbon was reduced to 0.35 per cent., the 
middle still remaining at 1.55 per cent. The compo- 
site mass was then quenched, polished and scratched 
with a needle. M. Osmond then found that the 0.37 
per cent. region was harder than the 1.55 per cent. 
region, and hence that ‘‘ austenite ’’ is soft. No proof 
is given that in the high carbon region the separation 
of graphite had not been brought about by the anneal- 
ing. However, no practical steel metallurgist can 
believe that a 0.37 per cent. carbon steel, rapidly 
quenched from 1050°, is harder than a 1.55 per cent. 
carbon steel quenched under the same conditions, be- 
cause it has been frequently established that the latter 
will scratch quartz (7) and the former only apatite (5). 
Concerning hardness, M. Osmond says on p. 83 
that cementite has a hardness of 6 (felspar), and is 
harder than quenched steel. It is well known to 
mineralogists that the best classes of pen-knife blades 
(which have been tempered) have a hardness of 6 to | 
No. 1798, VOL. 69] 
6.5, and that fully hardened steel has a hardness at 
least equal to that of quartz (7). r 
In connection with’ micrographic definitions it is 
interesting to note that within a year two books deal- 
ing with the microstructure of metals have been pub- 
lished by prominent members of the allotropic school, 
namely, the work under review and one by Prof. Howe. 
It will be well here to quote the respective definitions 
given as to the nature of austenite. 
Osmond (p. 98).—‘‘ To obtain it’’ (austenite) ‘‘ the 
temperature of the steel must be above rooo° and the 
temperature of the quenching bath a little below, or 
just at, o° C., and the proportion of carbon must exceed 
I-I per cent.”’ 
Howe, ‘‘ Iron, Steel and other Alloys ’’ (p. 179).— 
“ Austenite, the characteristic and chief constituent of 
suddenly cooled, i.e. ‘ hardened ’ steel, is a hard, brittle 
mass, with a needle-like structure, and is a solid solu- 
tion of carbon in iron, the proportion of carbon varying 
from nothing up to about two per cent.” 
Of allotropic definitions, students of metallography, 
somewhat modifying the words of Enobarbus, may 
well say :— 
““Truth cannot wither them, nor custom stale 
Their infinite variety.”’ 
Also Prof. Howe’s reference to ‘‘a solid solution of 
carbon in iron ’’ containing no carbon seems distinctly 
Hibernian. 
All students should obtain M. Osmond’s book. His 
brilliant and valuable thermal work and the charm of 
his ingenuous writings have made him many friends 
amongst those who strenuously oppose his theories and 
nomenclature. His book gives a fairly clear enunci- 
ation of his views, which are now accessible to all, 
whereas before they had been fully set forth only to 
those familiar with his original memoirs in French; 
nevertheless, a perusal of his book will reveal to many 
metallographists the fact that his patient work has 
been carried out in an environment perfectly detached 
from the stern actualities of the great world of 
practical steel metallurgy. J. O. ARNOLD. 
ZOOLOGICAL ESSAYS. 
Mostly Mammals. Zoological Essays. By R. 
Lydekker. Pp. ix+383; with sixteen full-page illus- 
trations by the Duchess of Bedford, Lord Delamere, 
the Hon. Walter Rothschild, J. Wolf, and others. 
(London: Hutchinson and Co., 1903.) Price 
12s. 6d. 
HOSE who already know these zoological essays 
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those who have not previously discovered them in 
‘periodical literature may be envied their treat in store. 
For the essays are at the high-water mark of zoological 
exposition; they are vividly interesting, yet scrupu- 
lously accurate; they are rich in fresh facts, salted 
with big evolutionary ideas. The author is well known 
as one of the foremost experts on mammals, and he 
has exhibited for many years the great gift of discuss- 
ing difficult problems ‘‘ popularly,’’ without blunting 
the edge of his scientific thoroughness. 
Some of the essays discuss man’s influence in ex- 
