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OT and OTA test

OT Test enables Total, free and combined chlorine in water
The reagent is ‘analytical grade Orthotolidine’, dissolved in 10% solution of HCl
When this reagent is added to the water containing chlorine , it turns yellow
The intensity of yellow colour is proportional to the concentration of chlorine
This yellow colour is produced by both free and combined chlorine residuals
However, OT reacts with free chlorine instantaneously but reacts more slowly with combined chlorine
Add 0.1 ml of reagent to I ml of water
Yellow color is produced and matched against charts within 10 sec, this gives the amount of ‘free chlorine
The yellow color appearing after a few minutes, gives the amount of ‘Total chlorine
The orthotolidine test, however, is not accurate, because the impurities such as iron, manganese, nitrate etc., are likely to cause a false yellow color, and indicating wrong and increased chlorine residual
Orthotolidine Arsenite Test (OTA test)
This is an improvement of the OT test
The levels of the free and combined chlorine residual are determined as in the OT test
Next, the water sample is dechlorinated and the test repeated
The yellow colour produced NOW is caused by the presence of other interfering substances such as nitrites, iron and manganese
This level is subtracted from the free and combined residual chlorine levels to obtain the true residual levels
Hence the error is overcome

OT and OTA test:

Membrane processes in water purification:

Super Chlorination and Break Point Chlorination:

Slow sand filter:

Rapid sand filter:

Purification of water at a large scale:

Criteria for a Chemical to be Suitable as Water Disinfectant in Water Supplies:

Water Supplies Disinfection with Chlorination:

Principles of Chlorination:

Methods of Chlorination in Water Supplies:

Horrock's Apparatus:

Disinfection of well during emergency:

Double Pot method:

Disinfection of Wells:

OT and OTA test:

Domestic or Household Purification of Water: