Page 100 - Vogel's TEXTBOOK OF QUANTITATIVE CHEMICAL ANALYSIS

3 COMHON APPARATUS AND BASIC TECHNIQUES

to each determination, the title of which, together with the date, must be
clearly indicated. One of the two pages must be reserved for the experimental
observations, and the other should be used for a brief description of the
procedure followed, but with a full account of any special features associated
with the determination, In most cases it will be found convenient to divide
the page on which the experimental observations are to be recorded into two
halves by a vertical line, and then to halve the right-hand column thus created
with a second vertical line. The left-hand side of the page can then be used
to indicate the observations to be made, and the data for duplicate
determinations can be recorded side by side in the two right-hand columns.
The record must conclude with the calculation of the result of the analyses,
and in this connection the equation(s) for the principal chemical reaction(s)
involved in the determination should be shown together with a clear
exposition of the procedure used for calculating the result. Finally, appropriate
comments should be made upon the degree of accuracy and the precision
achieved.
Many modern instruments used in the analytical laboratory are interfaced
with a computer and a printer provides a permanent record of the
experimental data and the final result may even be given. This printout should
be permanently attached to the observations page of the laboratory record
book, and it should be regarded as normal practice to perform a 'rough'
calculation to confirm that the printed result is of the right order.
8. Safety procedures must be observed in the laboratory at al1 times. Many
chemicals encountered in analysis are poisonous and must be carefully
handled. Whereas the dangerous properties of concentrated acids and of
widely recognised poisons such as potassium cyanide are well known, the
dangers associated with organo-chlorine solvents, benzene and many other
chemicals are less apparent.
Many operations involving chemical reactions are potentially dangerous,
and in such cases recommended procedures must be carefully followed and
obeyed. Al1 laboratory workers should familiarise themselves with local safety
requirements (in some laboratories, the wearing of safety spectacles may be
compulsory), and with the position of first-aid equipment.
For further guidance it is recommended that some study should be made
of books devoted to hazards and safe ~ractices in chemical laboratories.
Some institutions and organisations issue booklets dealing with these matters
and further information will be found in citations 12- 17 of the Bibliography,
Section 3.39.

BALANCES

3.2 THE ANALYTICAL BALANCE
One of the commonest procedures carried out by the analyst is the measurement
of mass. Many chemical analyses are based upon the accurate determination
of the mass of a sample, and that of a solid substance produced from it
(gravimetric analysis), or upon ascertaining the volume of a carefully prepared
standard solution (which contains an accurately known mass of solute) which
is required to react with the sample (titrimetric analysis). For the accurate