what happens to the stability of a conical flask when more water is added
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Chapter 7 - PHYSICAL AND CHEMICAL ANALYSES
This chapter was prepared by R. Ballance
In compiling this chapter, care has been taken to avoid procedures that require delicate or
sophisticated equipment. For many of the variables for which methods of analysis are
presented here, further information relating to their selection and inclusion in water quality
monitoring and assessment programmes (such as their environmental significance, normal
ranges of concentrations, and behaviour in the aquatic environment) can be found in the
companion guidebook Water Quality Assessments.
7.1 Preparation and use of chemical reagents
The following general rules should be followed in the preparation and use of chemical
reagents. The best quality chemical reagents available should be used - normally “analytical
reagent grade”. For most laboratory purposes, water distilled in a borosilicate glass still or a
tin still will be satisfactory. For preparing some reagents, dilution water requires special
treatment, such as a second distillation, boiling to drive off CO2 or passing through a mixed
bed ion exchanger. Where such special treatment is necessary, this is stated.
Recipes for the preparation of reagents usually give directions for the preparation of a 1-litre
volume. For those reagents that are not used often, smaller volumes should be prepared by
mixing proportionally smaller quantities than those given in the recipe. Where a working
standard or working solution is to be made by dilution of a stock solution, no more of the
stock solution should be prepared than will be used within the next six months. Furthermore,
only the amount of stock solution necessary to meet the immediate need for a working or
standard solution should be diluted at one time.
Reagent solutions should be kept in tightly stoppered glass bottles (except where they are
incompatible with glass, as with silica solutions). Rubber or neoprene stoppers or screw tops
with gaskets are suitable, provided that the reagents do not react with these materials. For
short-term storage, for example during a field trip of a week or two, small quantities of
reagent may be transported in plastic bottles with plastic screw caps.
Reagent containers should always be accurately labeled with the name of the reagent, its
concentration, the date that it was prepared and the name or initials of the person who
prepared it.