EDITORIAL. 
95 
effervesce when mixed with water and acetic acid. When moistened and 
examined by the microscope in day light, it appears of a pale yellow color 
and is found to consist of a flocculent or minutely granular substance in- 
termixed with fragments of prysmatic crystals (similar to those found in the 
light carbonate of magnesia.) See figure 1. 
Figure 1. 
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Figure 2. 
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" Heavy Calcined Magnesia. (Magnesia Calcinata ponderosa.) This is some- 
times called condensed calcined magnesia. It is a harder, firmer, purer, and 
heavier preparation than the preceding. None of the commercial samples 
which I have examined contain so much carbonate as the common calcined 
magnesia, and do not therefore effervesce so freely when mixed with water 
and acetic acid. Some of the samples which I have met with, are, to the 
naked eye, quite pulverulent: others are composed of little lumps or masses 
formed by the cohesion of the powder, and which have sufficient hardness to 
produce a ringing sound when shaken in a glass bottle. On the label of one 
specimen of this kind which I have met with, it is stated that one part in 
bulk is equal to three parts of the common calcined magnesia. When moist- 
ened and examined by daylight with the microscope, Howard's heavy cal- 
cined magnesia is seen to consist entirely of yellow minute granules, more 
or less cohering into small masses : no fragments of crystals were perceptible 
in it. (See Fig. 2.) The samel found to be the appearance of other com- 
mercial samples of heavy calcined magnesia, as well as of Henry's Calcined 
Magnesia,- 15 
The application of the microscope, in discovering the characters, and in 
ascertaining the genuineness of drugs, etc., has been extensively brought to 
his assistance by our author. 
The numerous and valuable improvements in the first volume or inorganic 
part, in which, usually, changes are less apt to be needed, lead us to an- 
ticipate a great accession of interesting subjects in the second volume on 
organic drugs. We have reason for believing, from the numerous contri- 
butions of Dr. Pereira to the Pharmaceutical Journal, that he has subjected 
the work to a most thorough examination, and the interesting contributions 
from the East, South America, and the Indies, which were attracted to 
London by the World's Exhibition, will doubtless be made use of when 
their interest or value demands it. Besides, it will be in the second volume 
more especially that the additions from the pen of Dr. Carson will appear. 
When completed, therefore, this work of Dr. Pereira will be beyond all 
