48 
THE AUSTRALASIAN JOURNAL OF PHARMACY. 
Preliminary experiments (or dry reactions, as they are called) upon the 
substance under examination are of great moment, as it aids the student very 
much in affording indications of what particular processes of separation should 
be employed. To furnish an instance : blow-pipe reactions would inform him 
whether copper or mercury be present, and a knowledge of this is requisite in 
the choice of a re-agent to separate arsenic, antimony, and tin sulphides from 
those of the copper and mercury divisions, otherwise clean separations cannot be 
carried out. The flame tests of volatile salts are very useful to give a clue to 
the presence of certain metals, as copper, barium, lithium ; while Browning’s 
direct vision spectroscope is exceedingly handy and valuable in discerning by 
means of the lines in the spectrum what metals are imparting the colouration, 
since there are various greens, crimsons, etc., produced in the flame. Then we 
have incrustations on charcoal, borax beads in the oxidizing and reducing flame 
respectively, and the nature of metallic beads or residues produced on charcoal 
with the aid of fluxes, from all of which very good inferences may frequently be 
drawn. The observation of sublimations or metallic mirrors when the substance 
is heated in a bulb tube alone, or with the aid of fusion mixture, is specially 
important, and requires the exercise of great care. Water of crystallization is 
also detected in the same way, but should in every case be removed from the 
neck of the tube by a slender roll of bibulous paper, so that deposition of 
sublimates may be clearly seen. All such trial tests should be duly recorded in 
the laboratory note-book in three parallel columns, thus : — 
Experiment. | Observation. | Inference. 
Some tutors recommend this preliminary work to be done during the 
process of separation in the wet way, as when filtrations and washing of 
precipitates are going on, but such plan loses all the value of the work. 
Some students, from sheer laziness, only perform one or two dry reactions 
after the examination in the regular wet method, and then “ cook ” their 
report to accord with the results found. Any experienced examiner can at 
once detect such fraudulent representations, as they may be truly termed. 
In many university laboratories the student analyses his mixture, and goes 
to the demonstrator to declare the results obtained. He is merely asked 
what he has found, and never questioned as to the modus operandi , and then 
he is told “right” or “wrong,” “repeat,” or “pass on,” as the case may 
be ! Such lax system never discovers whether the pupil has performed his 
work in a conscientious or honest fashion. Students are not infallible, and the 
writer’s experience, both as a student and teacher in various laboratories, has 
clearly proved that unfair means are adopted. The student should work 
straightforwardly, and not quiz his neighbour as to what he has found in a 
certain sample. He ought to save, if convenient, his precipitates, his beads, 
and colour tests until the whole investigation is completed, not only for further 
reference himself, if necessary, but that the overseer can see them in case of 
doubt, and criticise his work. 
Another important point for the beginner is to learn to discriminate between 
real constituents and traces of other bodies, or accidental impurities introduced 
by careless manipulation. To avoid the last named it is essential at the outset 
that all test tubes, evaporating basins, and funnels be thoroughly cleansed, that 
the re-agents be pure and the solutions clear, and made with distilled water. 
Then the re-agent bottles on the shelves must be kept clean, especially about the 
necks, and the stoppers free from dust. The next thing is to know how much 
of the sample should be worked with. A common mistake is to start with too 
large a quantity of the substance to be tested, whereby much loss of time 
