406 
only method by which we could endeavour to form 
any estimate of the relative volume occupied in a com- 
pound by the constituent atoms would be by taking the 
molecular volume of the compound and the atomic 
volumes of the constituents into account; but this 
is never done. It would be a great advantage if we were 
to cease using the term volume when speaking of gases, 
and were to treat all questions concerning changes in 
volume froma dynamical point of view: Avogadro’s law 
tells us, in fact, that, in every change in which gases are 
concerned, the variation in the space required to contain 
the gases—pressure and temperature remaining constant 
—will be directly as the variation in the number of 
gaseous molecules. If the equation be written which 
expresses the change, care being taken to employ the 
symbols which represent the molecular composition of 
the gaseous substances concerned in it, it is merely neces- 
sary to add up the number of molecules of the gaseous 
substances appearing on either side: the two sums will 
give the ratio of the volumes before and after change. 
By our present practice thoroughly false conceptions are 
engendered: a fundamental principle of our science is 
most unscientifically taught: and yet when we come to 
examine we marvel at the stupidity displayed by the 
examinee when dealing with simple questions of volume 
change ! 
NATURE 
It will be in place here to inquire—What is chemzcal | 
physics? To judge from the books on the subject, we | 
are probably justified in defining it as a milk-and-watery 
kind of physics specially prepared to suit the weak diges- 
tion and small appetite of the embryonic chemist ; as a 
spineless kind of physics—physics without the solid back- | 
bone of mathematics. It is high time that it were recog- 
nised that he who wishes to be a chemist, and not the 
mechanical automaton who too frequently in this country | 
goes by the name, must study physics seriously and 
properly: a mere smattering is of very little use. It is 
now incontestable that the sciences of chemistry and 
physics are inseparable: indeed the whole system of | 
modern chemical theory reposes on a purely physical 
basis—that of Avogadro’s law; and of late years the 
opinion has undoubtedly gained ground that the study of 
the physical attributes of pure elements and compounds 
must be carried on systematically and at the same ‘time 
that their strictly chemical attributes are investigated, if 
we are ever to penetrate the veil of mystery which at 
present enshrouds the simplest chemical phenomena. 
Much work has already been done, and it is greatly to 
the credit of chemists that it has nearly all been executed 
by chemists who have been at the pains to study physical 
methods. Physicists have contributed comparatively 
little to the advancement of chemical physics, and it is 
undeniable that not a few investigations of importance 
to chemistry executed by physicists with the precision in 
measurement which characterises modern physical in- 
quiry, are to a large extent labour spent in vain, as no 
guarantee has been given of the purity of the materials 
employed. Parenthetically it may be added that the 
physics as well as the chemistry of fre substances are 
fields of inquiry all but untrodden: the study of pure 
materials is ##e work of the future; and it is safe to 
say that when the results are recorded they will differ 
in many and important particulars from those now 
[Seft. 2, 1886 
accepted. It is perhaps not undesirable to point out that 
a true conception of the meaning of the word pure does 
not always appear to be present in the mind of the 
chemist or physicist, otherwise the expression “ chemi- 
cally pure” would not so frequently occur. What is 
meant thereby, we presume, is that the substance is so 
nearly pure that the amount of impurity present does not 
perceptibly affect the results of quantitative analysis ; but 
the amount of impurity present in a substance in such a 
case may exercise a most important influence on its 
chemical behaviour, and may also materially modify 
some of its physical properties. If, instead of distinguish- 
ing degrees of impurity, we continue to make this some- 
what improper use of the word pure, it will be desirable 
also to speak of substances as being “ spectroscopically 
pure,” “ electrically pure,” &c., to indicate the nature of 
the test which they will pass. 
To conclude, a book worthy to be called a treatise on 
chemical phys ics has yet to be written. It should con- 
tain a sufficiently detailed account of exact methods of 
determining the various physical attributes and the trust- 
worthy results thus far recorded, together with a discus- — 
sion of the bearing of these results on the problems of 
chemistry. It could hardly be the work of a single indi- 
vidual, but would doubtless require the co-operation of 
chemist and physicist. No mere compilation will suffice : 
to be of value it must be subject to the control of a 
chemist who is master of his science. Such a work 
would of necessity be of enormous service to students ; 
and it would exercise an important influence on the 
progress of our science. HENRY E. ARMSTRONG 
OUR BOOK SHELF 
Madagaskar, und die Inseln Seychellen, Aldabra, Komo- 
ren, und Maskarenen. By Prof. Dr. R. Hartmann. 
(Leipzig and Prague, 1886). 
Tus little work forms the fifty-seventh volume of “ Das 
Wissen der Gegenwart,” a scientific series which has 
already done so much for the spread of useful and 
accurate information amongst the Germanic populations. 
The author, himself personally acquainted with some of 
the localities here described, gives as clear and compre-— 
hensive an account of the various insular groups in the 
Indian Ocean as was possible within the available space d 
of 150 pages. Of this space over two-thirds are devoted 
to Madagascar, whose physical constitution, natural 
history, ethnology, and political relations are treated — 
with great ability. The best authorities, such as Gran- 
didier, Shaw, Richardson, Sibree, and Hildebrandt, have © 
been carefully consulted, and room has even been found | 
for the discussion of such controversial questions as the — 
existence of Sclater’s vanished Lemuria, the origin of the : 
Malagasy people, the affinities of their language, the 
presence in the island of the Vazimba and other abori- 
ginal non-Malayan and Negrito tribes. Dr. Hartmann is — 
inclined to accept the statements made by Commerson 
and Modave regarding the woolly-haired and dwarfish 
Kimo people of the southern districts, and suggests 
possible affinities either with the South African Bushmen — 
or the Andamanese and Aeta Negritos of the Philippine” 
Islands. The Malagasy he regards as essentially a 
mixed race, Polynesian, Malay, and African (especially 
Galla and Somali) elements being found diversely inter- 
mingled amongst the Hovas, Sakalavas, Betsimisaracas, 
and other native communities. The Comoros, Seychelles, 
and Mascarenhas (Mauritius, Réunion, and Rodriguez) 
| 
