Describe how you would carry out any these of the following tests in a sample of boiler water.
1. hardness
2. alkalinity
3. chlorides
4. excess phosphate
5. excess sulphites
6. pH
7. dissolved oxygen
HARDNESS TEST:
• Take 100ml of boiler water sample
• add 2ml at a time of standard soap solution
• shake vigorously after each addition of soap until lather persists for at least five minutes
• calculation____-ml of soap solution used x 10= ppm CaCO3 equivalent
A waters ability to form a lather with soap depends upon the hardness salts which are present,
hence the quantity of soaps solution used is a direct measure of the hardness salts in the sample
ALKALINITY:
ALKALINITY TO PHENOLPHTHALEN
• Take 100ml sample of boiler water
• added N/50 sulphuric acid to clear the sample
• calculation__ml of N/50 acid used x 10= ppm CaCO phenolphthalum is less alkaline than
hydroxides or carbonate, and when it is added to a sample containing hydroxides and or
carbonate it will turn pink in color. The acid used after this coloration will first the
hydroxides forming salts. It will then react with the carbonate present forming
bicarbonate molecule. Bicarbonate molecules are less alkaline then phenolphthalum,
hence the pink coloration will disappear once all the hydroxides and carbonate have
been dealt with by the acid. Once bicarbonate molecules is formed the quantity of acid
used is a measure of the alkalinity due to the hydroxids (caustic)present and half the
carbonates
TOTAL ALKALINITY
• Take alkalinity to phenolphthalum sample
• add 10 drops of methyl-orange resulting in yellow coloration
• add n/50 sulphuric acid until pink
• calculation _____ml of N/50 acid used for both test x 10= ppm CaCO3
Methyl-orange indicator is less alkaline than phenolphthalum and bicarbonates. It can be used
initially in place of phenolphthaling or as is more normal as a continuation after the alkalinity to
phenyolphthalum test. If no yellow coloration result when methyl-orange is added to the
alkalinity phenolphthalum sample no bicarbonate are present hence no carbonates are present.
Therefore the alkalinity as determined in the alkinility to phenolphthalin test, been due to
hydroxides above. Note: hydroxided and carbonates can co-exist together in a solution, but
hydroxide and bi-carbonates cannot.
CAUSTIC ALKALINITY
• Take 100 ml sample of boiler water
• add 10ml of barium chloride
• add 10 drops of phenolphthalic, resulting in pink coloration
• add N/50 sulphuric acid to clear sample
• calculation______ml of N/50 acid used x 10 = ppm CaC...
In this test burium chloride is first added to the .............carbonate which are present. The test is
then carried out as for the alkalinity to phenolphthalum test but in this case only the hydroxide (
caustic) will be measured.
3) CHLORIDE TEST:
• Take alkalinity to phenolphthalin sample
• add 2 ml of sulphric acid
• add 20 drops of potassium chromate indicator
• add N/35.5 silver nitrate solution until a brown coloration results
• calculation_____ml of N/35.5 solution used x10= ppm CaCO3
Chlorides may be present in the boiler water sample and it is essential that they be measured as
they would be an indication of salt water leakage into the feed system, either a leaky condenser
or a primed evaporator. The alkalinity to phenolphthalum sample taken has hydroxides and
carbonate dealt with and they will play further part in test no conducted for chloride the
sample is made definitely acidic by the addition. A further small quality of acid, this is to speed
up the chemical reaction which next takes place. Silver nitrate has an affinity for potassium
chromate and chloride, its principal preference however is for the chlorides. When it has
neutralized the chlorides present in the sample, it is then free to react with the potassium
chromate, in doing so it produces a reddish brown coloration. It is therefore apparent that the
amount of silver nitrate solution used is a direct measure of the content of the boiler water
sample reddish brown local coloration results which quickly disappears if chlorides are present.
This should be ignored.
4. PHOSPHATE TEST
• take 25 ml of filtered boiler water sample
• add 25 ml vanodomolybdate reagent
• fill comparator tube with this solution and place in right hand compartment of
comparator
• in left had compartment place a blank prepared by mixing equal volumes of
vanodomolybdate reagent and demonized water.
• allow color to develop for at least 3 mins and then compare with disc.
• calculation: phosphate reserve in ppm from the disc reading
5. EXCESS SULPHITES:
• Take 100ml of boiler water sample, add 2ml of sulphric acid
• add 1ml of starch solution
• add potassium iodide - iodate solution until sample is blue in color
• calculation: ml of iodide - iodate solution used x 120?= RPM Na2SO3 (sodium sulphate)
The boiler water sample is made slightly acidic to speed up the chemical reactions which are to
take place. Potassium iodide - iodate produces a blue coloration through reaction with starch,
but it has a preferential chemical reaction with sulphate it is present in the sample. Hence when
the potassium sulphate present it is then free to react with the starch present in the sample,
producing a blue coloration. It is therefore apparent that the amount of potassium iodide-iodate
solution used is a direct measure of the sulphite content on the boiler water sample. As far as is
possible, the atmosphere should be excluded in this test otherwise an incorrect result may
occur. If the test indicates that an adequate reserve of sodium sulphite is present in the boiler
water there in no need to conduct a test for dissolve oxygen
6. PH VALVE
A boiler water pH valve can be obtained by three basic methods:
1 litmus paper
2 colourimeterically
3 electrolytically
LITMUS PAPER
These are used to ascertain the degree of acidity of alkalinity of the boiler water. A litmus paper
when inserted into a sample of boiler water makes changes in color, turning blue if the water is
alkaline or red if the water is acidic. The degree of coloration is very rough indication of the PH
valve of the boiler water.
COLOURIMETRIC METHOD
Take a sample of boiler water. Place one thymol blue tablet in a 50 ml cylinder. Add 50 ml of
boiler water sample to dissolve cylinder and ensure tablet is dissolved into the other cylinder.
Place first sample in right hand compartment of nessleriser. Place second sample in left hand
compartment of nesslerier. Place approximate disc in nessleriser and match the colors then read
the PH valve from the right hand window.
ELECTROLYTIC METHOD
An electric cell, using the boiler water as an electrolyte and two special electrodes, both made of
glass are used. The potential difference between the electrodes id directly dependent upon the
hydrogen control of the electrolyte (boiler water). The potential difference is measured by a
sensitive voltmeter connected into the external circuit of the cell and calibrated to read pH
valves.
7. DISSOLVED OXYGEN
Take 500ml of boiler water sample, add 0.3ml of manganese chloride, add 0.3 ml of potassium
hydroxide, add 1 ml of hydro-chloride acid, and add 2 ml ortho tolidine. In this test it is essential
the atmosphere be excluded from the sample being tested. To arrange for this a special
designed sampler flask is used. After the addition of various chemicals to the boiler sampler, the
resulting solution is compared colour metrically with a color chart or a series of indicator
solutions whose dissolved oxygen content is known. Where colors of sample and indicator
coincide, the dissolved oxygen content of the boiler water sample is used from the indicator.
