SCIENTIFIC GLASSWARE
An Introduction to Small Scale Chemistry
By Prof. B. Ternai
DCE, B.Sc., M.Sc., Ph.D., FRSC, C.Chem., FRACI
When the first laboratory handbook appeared, more than
a 100 years ago, the description of experiments in it reflected,
understandably enough, the industrial chemical background of the
science and practice of Chemistry at the time. While scientific
equipment manufacturers produced instruments, the quality of which
is still admired by modern instrument makers, the students and
instructors had to hand make the glassware, piece by piece, which
by necessity meant that not two pieces of glassware were identical
and the design of the glassware followed the individual requirement
of particular experiments. Contemporary drawings of chemical laboratories
(known as elaboratories) show young gentlemen in morning suits
and top hats observing experiments carried out (most of the time)
by assistants. The scale of the experiments would have bankrupted
a modern Chemistry Department, as they were conducted on an almost
industrial scale. The students had to prepare their chemicals
and reagents themselves, starting with only a few, then commercially
available, chemicals, such as coal tar and a few crude, industrially
used products. As yields were considered to be not much of a concern
and the reactions themselves were not yet properly explored, yields
were often abysmal. Under those conditions the use of large scale
preparations were considered the norm, rather than the exception,
since one product could then be used as the starting material
for the synthesis of some other, often not commercially available,
compound. This situation has not changed from the last quarter
of the 19th Century to the 1950s. Classic "Experimental Organic
Chemistry" textbooks such vs Hickinbottom, Houben-Weyl, and
Vogel dominated the laboratory instruction. All of these were
on the 10 to several 100g. scale, with solvents often used by
the liter. It is fascinating to find that at the very same period
of time, some of the great natural product chemists, such as Butenandt,
Kamer and Ruzicka regularly worked on a truly micro scale. An
example might be the determination and structural characterization
of the retinal pigment of butterflies after paper chromatography
of their eyes. parallel with this work the analytical chemists,
and in particular Pregl, fiercely competed with each other for
the glory of being able to identify (and characterize!) diminishingly
smaller and smaller amounts of chemicals, often on a milligram
or even smaller scale. Outstanding examples of small scale experimentation
are the books by Cheronis and Ma. In fact American and European
Universities competed with each other in the operating skill of
their students: witness the annual crystallization competition
of students at the Fiesers' laboratory and our own requirement
to fractionate 3 drops of a solvent mixture using equipment made
by ourselves. Glassblowing had been taught at the senior level.
The introduction (in the middle of the 1950's) of factory made,
relatively large scale interchangeable glassware with standard
joints by Quickfit put a virtual stop to advances towards the
development of small scale glassware. Not until about 35 years
ago, when safety and environmental concerns begun to demand the
reduction of waste and chemicals in the environment, did commercially
available small and micro scale equipment became available. In
spite of all this, the vast majority of laboratory textbooks today
still prescribe their operations for the 5 -20 g scale, using
glassware of 50 - 250 and sometimes up to 500 ml capacity.
What is the justification, if any, for using such large
amounts of chemicals?
The amounts are easier to weigh accurately.
Transfer losses are usually not significant.
Obtaining a pure product is easy, but not necessarily
efficient.
Several recrystallization or distillations would
surely yield a pure product - even though in much reduced quantities.
(No doubt the Fiesers had this in mind when they set their requirement
for both highest purity and highest yield in their end of year
student competitions.)
Less well equipped institutions often require wet
chemical derivatization and identification of end products for
educational reasons.
It is often difficult to obtain the necessary funds
for the purchase of a large number of small scale glassware while
the large scale glassware is still serviceable.
What are the reasons for reducing the size
of chemical laboratory experiments?
The main reasons are safety, economy and speed.
In larger laboratories, often accommodating 25
- 50 students, the amount of solvents or other volatile chemicals
handled during a 2 - 4 hrs long laboratory session will inevitably
lead to their volatilization to a significant extent and eventual
exposure of the students and staff to toxic vapors.
As an example, acetone, a common solvent, has a TWA of 500 ppm
and a Ceiling Limit of 750 ppm which- of course, must not be exceeded.
This amount corresponds to the contents of one small wash bottle
when related to a standard size laboratory. Considering the high
vapor pressure of most of the solvents used, at around 30 degrees
centigrade. the presence of this amount in the laboratory air
would break the law. Of course, this is only one chemical of relatively
low toxicity among the many additional chemicals used in laboratory
student experiments.
The disposal of end- and by-products, solvents,
reagents etc. is an increasingly regulated activity. Reduction
of the amount of chemicals used in the first place also reduces
the waste disposal problem to manageable proportions.
Laboratory operations, such as heating and cooling,
addition of reactants, efficiency of mixing, filtration etc. are
typically dependent of the 3rd power of the volume used. Thus
reduction of the volume of the glassware results in a drastic
reduction of the experimental time needed, enabling the students
to perform experiments which were previously considered to be
too time consuming for one laboratory session.
Alternatively, the time gained can be utilized for writing up
laboratory reports or longer, more effective interaction of the
staff with the students.
The reduction of the amounts of chemicals used,
provides at least two benefits there is an immediate, clearly
visible, saving on chemical costs, and it allows to perform some
experiments which were previously considered to be too expensive
to carry out on a tight budget.
