FEBRUARY 15, 1901.] 
illustrated section headed ‘Technique and 
Experiments’; these sections are very pleasing. 
The apparatus is of the most modern type, 
many experiments are new. 
The author had Professor Ramsay’s coopera- 
tion in rewriting the chapter on noble gases 
for this edition. The chapter includes full 
illustrated descriptions of the methods for 
obtaining argon and helium, and colored tables 
of the spectra of all the noble gases, showing 
the three spectras of argon—the blue, the red 
and the green. Another interesting chapter 
is that devoted to flame, illumination, photom- 
etry, burners, furnaces, fuel gases, fuels and 
heat values. In this, as indeed in the whole 
book, we find the newest methods and the latest 
statistical results. Striking examples of this 
are shown in the references to persulphuric acid 
and to radium; in the first instance the work 
of Baeyer and Villiger on ‘Caro’s Reagent’ 
in the Berichte of June 7th is utilized for the 
book which appeared in October; in the latter 
instance we find in the chapter on barium a 
brief discussion of radio activity, radium and 
polonium and of the work of Becquerel, of the 
Curie’s and of Lengyel. 
Of more vital importance to the student are 
the methods of formation of substances and 
their use in modern technical chemistry, which 
are not found in any other text-book. For 
example, recently published books state that 
hydrochloric acid is obtained technically only 
as a by-product in the Leblanc process. Erd- 
mann says that while in England one-half 
million tons of salt are used yearly for Leblanc 
soda, in other countries this process has only 
‘historical interest.’ Hydrochloric acid, he 
says, is now made in Germany either as a by- 
product in the Glauber salt industry from salt 
and sulphuric acid, or by decomposing magne- 
sium chloride with superheated steam. We 
find that magnesium chloride is obtained from 
Strassfurt Carnallite as by-product in ecrystal- 
lizing potassium chloride from Carnallite solu- 
tion or as a by-product in the manufacture of 
Glauber salt by action of a solution of Strass- 
furt Kieserite on salt at low temperatures, 8,000 
tons Glauber salt being made yearly by the 
latter method. 
The theoretical side of the book is also well 
SCIENCE. 
269 
developed. Physical chemical theories are, it 
is true, but little utilized. The author ex- 
plains the theory of ions briefly under the head 
of acids, and refers to this and other theories 
from time to time throughout the book, devot- 
ing seven pages at the end to a condensed dis- 
cussion of the laws of electro-chemistry and of 
electrolytic dissociation; that is all. But if 
weexamine Erdmann’s treatment of any class 
of compounds in detail we find that more space 
is given to the theoretical side—as we have 
hitherto been accustomed to define ‘theory ’— 
than by Ostwald, despite the demand of the 
latter author that a text-book of chemistry 
shall devote all its space to ‘pure chemistry.’ 
A comparison is justified by the decided 
stand both authors take. Both volumes are 
alike in size of page and type, Ostwald having 
795 pages and Erdmann 757. The reviewer 
has chosen at random the oxygen and hydro- 
gen compounds of nitrogen for the purposes of 
comparison. Ostwald devotes 36 pages to the 
subject; about one-half of this space is devoted 
to physical chemical considerations of great 
interest; the other half is descriptive chemis- 
try in the narrowest sense, no reference being 
made to any modern work on structure. Erd- 
mann gives 58 pages, of which 14 are given to 
illustrated experiment and technique ; the re 
maining 44 pages give fact, theory and statis- 
ties; he opens the subject with 5 pages de- 
voted to a study of the constitution of the 
compounds, relations of the different hydroxyl- 
acids, ete. Six pages follow on the formation, 
decomposition and properties of nitric acid, a 
full but carefully condensed statement. Ost- 
wald gives 13 pages to nitric acid, namely, 
composition HNO,, saltpeter, Chili saltpeter, 
decomposition of Chili saltpeter by sulphuric 
acid in two stages, and a few words on the 
properties of nitric acid. In short, no more 
than is contained in an average school chem- 
istry. Erdmann gives 4} pages to hydrazine 
and hydrazoic acid; Ostwald, 1 page. Erd- 
mann gives 2 to hyponitrous acid, explaining 
the stereoisomeric forms, which are ignored by 
Ostwald in the 15 lines given by him. 
In a recent review of Ostwald’s book it is 
said, ‘‘ Every chemist should own a copy of 
this book and should conscientiously study it.”’ 
