50 
On the same page a probable injustice is done to the 
instrument, for we find that ‘‘in all cases the observation 
must be often repeated to obtain results of any value.’ 
What can be meant by the statement on p. 198, that the 
octahedron, or unit pyramid, is always the largest, and 
the cube rectangular prism, or pinakoid the smallest, of 
the constituent forms of any combination? On p. 205 we 
learn that density and hardness are common to all solids 
alike, and are therefore zwdependent of structure. A 
definition (p. 212) informs us that a substance is ductile 
when it can be cut with a knife, but crushes to powder 
under a hammer, copper pyrites being cited as an ex- 
ample ; and on the same page we find as an illustration 
of toughness of a mineral that “ Malleable native Copper, 
especially when intimately mixed with siliceous vein-stuff 
and some varieties of Hematite and Iron Pyrites, has the 
property of toughness in a high degree.” 
The discussion of the optical properties is more un- 
satisfactory still. On p. 225 is to be found the following 
remarkable statement :— 
“The movements in such a medium can only be 
reduced to order by supposing them to be maae up of 
portions of homogeneous substances of different properties, 
and treating each one separately.” 
The proof of the existence of a minimum angle of 
deviation as submitted on p. 233 can scarcely be meant 
as serious ; but to this curious proof should not have been 
appended an erroneous translation of the formula into 
words. On p. 235 the azimuths of vibration of an ordinary 
ray of light are said to change continuously, but so very 
rapidly that the changes are not perceptible to the eye ; 
on the following page we read of “impulses having dif- 
ferent velocities.’ Perhaps matters reach a climax about 
p- 245, where the intelligibility of the book for a brief 
period suffers total eclipse, as perhaps may be imagined 
when we read that “these orthogonal forces are called the 
axes of optical elasticity.” On p. 263 one of the rays 
produced by double refraction is said to be “an extra- 
ordinary ray in all directions but those of the optic axes.”’ 
Phosphorescence is, according to p. 290, ‘‘the power of 
emitting light in a dark place.” On p. 293 we find a 
serious misapprehension as to the precise nature of the 
method employed by Fizeau for the determination of the 
expansion of crystals. One infers from the explanation 
here given that the interference rings, produced by help 
of a plane crystal surface and a lens, are dstorted on 
change of temperature, and that the measurement of this 
distortion serves for the determination of the coefficient of 
dilatation for different directions in the plane surface; as 
a matter of fact Fizeau by his method determined with 
each crystal section the dilatation in only ove direction, 
namely, that normal to the plane surface. 
It is difficult to understand how Mr. Bauerman has 
contrived to allow so many loose statements to creep into 
his book; and we can only surmise that he has himself 
not had the time or the opportunity for a careful revision 
of the proofs. At any rate it will be evident from the 
above that a careful revision is absolutely required before 
the book can take its proper place in mineralogical litera- 
ture. We trust that the present edition may be speedily 
disposed of, and that Mr, Bauerman will thus be enabled 
to offer to the English student a second and revised 
edition of a work, the want of which is urgently felt by 
every teacher of the subject. L, FLETCHER 
NATURE 
ey 3 a 
{| Mor. 17, 1881 
A TREATISE ON CHEMISTRY 
A Treatise on Chemistry. By H. E. Roscoe, F.R.S., and 
C. Schorlemmer, F.R.S., Professors of Chemistry in 
the Victoria University, Owens College, Manchester. 
Vol. III. The Chemistry of the Hydrocarbons and 
their Derivatives, or Organic Chemistry. Part I. 8vo. 
(London: Macmillan and Co., 1881.) 
HE term ‘‘ Organic Chemistry’’ was originally used 
to denote the chemistry of compounds produced in 
the living vegetable or animal organism, all of which 
contain the element CARBON. For a long time indeed it 
was supposed that these compounds were peculiarly the 
products of living organisms, being formed under the in- 
fluence of a so-called wztal force, and that they could not 
be produced, like those of the mineral world, by artificial 
means. But the course of research has shown that this 
idea was erroneous, and that a large number of the more 
important organic bodies—hydrocarbons, alcohols, acids, 
&c., originally known only as products of the living or- 
ganism—can be formed synthetically from their ultimate 
elements. The name ‘‘Organic Chemistry” has thus 
acquired a new signification, and in its widest sense is 
now used to denote the chemistry of carbon-compounds. 
As however some of these compounds, viz. the oxides and 
sulphide of carbon, have long been known to be producible 
by direct combination of their elements, and have accord- 
ingly been described in Manuals of Chemistry amongst 
inorganic compounds, the authors of the present treatise 
have thought it desirable to use the term “ Organic Che- 
mistry’’ in a somewhat narrower sense, viz. as signifying 
the CHEMISTRY OF THE HYDROCARBONS AND THEIR 
DERIVATIVES. 
The volume commences with a historical sketch of the 
development of this department of the science, tracing it 
from the few facts respecting organic bodies known to 
the ancients, to the discoveries of Scheele, Lavoisier, 
Berzelius, Liebig, and numerous other workers, down to 
the present time—dwelling especially on the idea of 
Compound Radicals introduced by Lavoisier, and further 
developed by Berzelius, and by Liebig and Wohler in 
their classical research on Bitter Almond Oil and its 
Derivatives, published in 1837—thence to the theories of 
Substitution and Types, founded chiefly on the researches 
of Dumas, and of Laurent and Gerhardt, and to the sub- 
sequent fusion of the Radical and Type theories brought 
about by the experiments of Williamson on Etherification, 
and those of Wurtz and Hofmann on the Compound 
Ammonias. 
The next division of the work treats of the methods of 
ORGANIC ANALYSIS, which are explained in considerable 
detail, and illustrated by admirable diagrams ; also of the 
determination of Vapour-density, in which the latest 
methods introduced by Victor Meyer are fully described, 
after which we come to the Determination of Molecular 
Formule, the explanations of which are characterised by 
singular clearness. 
Next follows the CLASSIFICATION OF CARBON-COM- 
POUNDS, which are divided into groups according to the 
mode of linking of the carbon-atoms, the principal divi- 
sions being the Fatty or Paraffin group, in which the 
carbon-atoms are joined together in a single open chain, 
and of the Aromatic or Benzene group, in which the 
