156 BOTANICAL GAZETTE [FEBRUARY 
and temperature control, discussion of reduction potential and its relation to 
hydrogen electrode potential, sources of error, standard solutions for checking 
such measurements, and a chapter on Px standardization, the last including 
” 
deals with the conductivity and other methods which have been used in special 
cases in estimating hydrogen ion concentrations. The final chapter on 
“Applications” groups the literature according to subject matter, and accord- 
ing to the author constitutes an index to the bibliography which follows. 
The reviewer was especially interested in the details which the writer has 
added from his experience in the manipulation of apparatus. Among these 
are the charging of storage batteries using an ordinary electric light current, 
the effects of various substances (carbon dioxide, phenol, toluol, oxygen, etc.) 
in solution upon the hydrogen electrode, purification of mercury, construction 
of a constant temperature box, and lists and discussion of possible potenti- 
ometer equipment. For the student already engaged in making hydrogen ion 
eterminations the book contains many valuable suggestions, and forms a 
ready reference to literature, while to the student who contemplates making 
such measurements it represents a manual, an outline of procedure.—J. M. 
ARTHUR. 
A chemistry of plant products : 
Haas and Hitr’s, An introduction to the chemistry of plant products, which 
first appeared in 1913 and was reviewed in this journal,3 has now reach 
second edition.4 From its first appearance it has been recognized as a book 
filling a long felt want. It was intended to supply the botanist, and especially 
the plant physiologist, with chemical knowledge and methods not found in 
the ordinary textbooks on chemistry, It has filled its purpose admirably. 
though written primarily for the plant physiologist, the avoidance of a 
technical method of treatment makes it a useful book for the botanist of limited 
chemical training, who is working on problems involving a knowledge of plant 
materials. Thus at the present time, when the synthetic viewpoint of botany 
in relation to the other sciences is coming to the front, when it is coming to 
be recognized that botany and chemistry must unite forces in solving many 
problems, the method of treatment used in the book has increased significance. 
It is a significant commentary on the amount of work being done by WILL- 
STATTER and his coworkers, and by others no doubt inspired by them, that 
major changes in the book have been made in the chapter on pigments. 
This chapter has been entirely rewritten and much new material incorporated, 
especially in the part dealing with chlorophyll. A few other important addi- 
tions have been made to the text, and a number of references have been added 
3 Bot. GAz. 56:343. 1913. 
4 Haas, PavL, and Hitt, T. G., An introduction to the chemistry of plant prod- 
ucts. 2d ed. pp. xiit411. London: Longmans, Green. 1917. 
