PREFACE TO THE FIFTH EDITION. 
The general design of the work has been maintained, the size 
but slightly increased, but much of doubtful practical utility 
has been omitted, and replaced by modern methods and 
researches. 
The use of the organic preparations of arsenic, antimony, 
and other inorganic toxic substances, the synthesis of highly 
active drugs, the standard processes of assay and the definite 
limitations of purity of a much-improved British Pharma¬ 
copoeia—all of comparatively recent origin—have been duly 
noted in the present edition. 
Recognising that mostly minute quantities of poison are 
recovered and have to be identified, the authors have laid 
stress on micro-chemical methods as well as “ physical 55 aids 
to identification, the latter having the advantage of not changing 
or wasting the substance. 
The authors trust that the various additions and altera¬ 
tions will be of utility and maintain the esteem in which the 
former editions have been held by the chemical and medical 
professions. 
3 Upper Gloucester Place, N.W. 1, 
August 1920. 
