NATURE 
THURSDAY, SEPTEMBER 2 
tj 
1886 
CHEMICAL PHYSICS 
Elements of Chemical Physics. By Josiah P. Cooke, 
Jr., Erving Professor of Chemistry and Mineralogy 
in Harvard University. Fourth Edition. (London: 
Macmillan and Co., 1886.) 
HE preface to this work bears the date Feb. 1, 1860 ; 
no explanation is given of the issue in 1886 of a 
fourth edition in the form before us. According to the dic- 
tionary, an edition is “the whole number of copies of a 
work published at once.” We are forced to assume that 
such a definition would be accepted as sufficient by Prof. 
Cooke ; but in the case of educational works dealing 
with a branch of science which is daily enriched by new 
discoveries, the reading public are in the habit of sup- 
posing that a zew edition is not a mere reprint of the 
former edition: it is rightly expected that it shall take 
notice of, at all events, the more important of recent dis- 
coveries, and failure to recognise this elementary truth is 
unpardonable. 
It is a grave injustice to put into the hands of the inno- 
cent student a book dated 1886 which was first issued in 
1860, and without informing him that he is to learn 
nothing of the classical discoveries in chemical physics 
made during the past quarter of a century : on advancing 
to do battle in the ranks of science he would be about in 
the position of our old wooden walls in face of modern 
ironclads and torpedo-boats. 
The work is divided into five chapters, the first (9 pp.) 
being introductory. Chapter II. (107 pp.) deals with the 
general properties of matter; Chapter III. (309 pp.) is 
on the three states of matter; heat is the subject of 
Chapter IV. (235 pp.); and Chapter V. (24 pp.) is on 
weighing and measuring. The volume is intended—ac- 
cording to the 1860 preface—to furnish a full development 
of the principles involved in the processes of weighing 
and measuring small quantities of matter ; subsequent 
volumes were to treat on light in its relations to crystallo- 
graphy ; on electricity in its relations to chemistry ; and 
on stoichiometry and the principles of chemical classifica- 
tion ; but we are not aware of their issue. Unlike most 
text-books, it is a most readable work, containing much 
interesting matter, and is admirably printed ; hence it is 
particularly to be regretted that it presents so imperfect 
and antiquated an account of the subjects treated of. In 
justification of this statement we may point out that the 
latest reference to experiments on the condensation of 
gases is to those of Natterer. Andrews’s great discovery 
of the critical point is nowhere referred to. Regnault’s 
determinations of the specific heat of carbon in its three 
forms are quoted, but not a word is said of Weber’s im- 
portant investigation on this subject; in the section in 
which the methods of determining specific heat are de- 
scribed no reference is made to Bunsen’s_ beautiful 
method ; and the word dissociation nowhere occurs, the 
classical discoveries of Deville and his school being un- 
mentioned. One inaccuracy requires special mention. 
We are told (p. 428) that, “ According to the modern 
theory of chemistry, equal volumes of all substances in 
the state of gas contain precisely the same number of 
VOL. XXXIV.—No. 879 
405 
molecules, 07, what amounts to the same thing, the mole- 
cules of all bodies in the state of gas occupy exactly 
equal volumes.” The latter part of the sentence, 
which we have italicised, is obviously unmitigated 
nonsense, yet it is a statement which perpetually 
haunts us. A well-known standard text-book of che- 
mistry from which probably a very large proportion 
of our youth gain inspiration in fact tells us almost 
in the same words that “the relation existing between 
the volumes of gases when they combine together has 
been found to be a very simple one, inasmuch as the 
densities of all elements known in the gaseous state are 
identical with their atomic weights ; or, what zs the same 
thing, the atoms in the gaseous state all occupy the same 
Space (Gay Lussac, Avogadro).” Could anything be more 
misleading and inaccurate, since mercury, phosphorus, 
sulphur and iodine are ail known “in the gaseous 
state”? It cannot be too clearly stated that the chemist 
only concerns himself with the relative weights of atoms 
and molecules, and that Avogadro’s law only has refer- 
ence to the relative numbers of molecules in equal 
volumes of gases, their size being altogether left out of 
account: no notice being taken, in fact, of the space 
which the stuff itself occupies. Our notions on the sub- 
ject of the size of molecules and atoms are of the very 
vaguest at present, and even Sir William Thomson has 
not ventured, we believe, to consider the differences in 
size of molecules of different kinds: for the most part 
they certainly cannot be of the same size. The popular 
method of teaching the volumetric relations between 
gases is probably the cause of the error now referred to 
being steadily perpetuated. The ordinary student more 
often than not will insist—very naturally—in regarding 
the term volume as representing a specific quantity : being 
taught, moreover, to consider the symbol of a compound 
gas as equivalent to “two volumes,” he extends the idea of 
volume to the elementary symbols and naturally enough 
concludes that if /:, for example, represent /zvo volumes, 
Z must represent ome volume; hence it is difficult to 
make him realise that a change such as is represented by 
the equation 4=/-+/7 involves a doubling of the 
volume. Again, the common practice of speaking of 
compound gases as containing certain volumes of the 
constituent gases is both misleading and inaccurate : for 
example, it is found that the gaseous density of phos- 
phorus is such that its molecular composition is expressed 
by the formula /,: this represents “two volumes,” and 
so the symbol P is said to represent “half a volume,” 
and we are then gravely told that “two volumes” of 
phosphuretted hydrogen comszsts of or contains “three 
volumes” of hydrogen and “half a volume” of phos- 
phorus. Some teachers engrave the error still more 
deeply upon the student’s mind by performing before him 
a kind of Jack-in-the-box trick, picking out from a box 
on which the symbol of the compound is painted a series 
of boxes which in number and size are supposed to repre- 
sent the volume of the elements contained in the com- 
pound. All that we really know is that a given bulk of a 
particular gas will decompose into, or can be formed 
from, certain bulks of the constituent elements: that 
phosphuretted hydrogen, to take the example cited, on 
decomposition yields one and a half times its bulk 
of hydrogen and half its bulk of phosphorus gas. The 
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