What is the unit of measurement for turbidity in this standard?

The unit is the Jackson Turbidity Unit (JTU).

What is the working principle of the Jackson Candle Turbidimeter?

It works on the principle of light absorption. The turbidity is determined by the depth of water required to make the image of a standard candle flame just disappear when viewed from the top.

Why is this method not used for drinking water testing?

Because the permissible turbidity for drinking water (e.g., 1 NTU per IS 10500) is far below this method's lower measurement limit of 25 JTU.

What is the difference between JTU and NTU?

JTU is based on light absorption (Jackson Candle method), while NTU (Nephelometric Turbidity Unit) is based on light scattering measured at 90 degrees to the incident light beam, which is a more sensitive and objective method.

IS 10053

: 1981

Requirements for equipment for Jackson candle turbidimeter and determination of turbidity

CurrentSpecializedTesting MethodEnvironmental · Public Health Engineering

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This standard specifies the requirements for the Jackson candle turbidimeter apparatus and outlines the procedure for determining turbidity in water. The method is based on measuring the length of the light path through a water sample at which the image of a standard candle flame just disappears. It is suitable for turbidities between 25 and 1000 JTU.

Requirements for equipment for Jackson candle turbidimeter and determination of turbidity

Quick Reference Values

Measurement PrincipleDisappearance of candle flame image through a column of water

Unit of MeasurementJackson Turbidity Unit (JTU)

Lower Detection Limit25 JTU

Upper Measurement Limit1000 JTU

Standard Suspension MaterialFuller's Earth or Diatomaceous Earth (Silica)

Standard Suspension Concentration1 g/L corresponding to 1000 JTU

Practical Notes

This is a historical and visual method, highly dependent on the operator's eyesight and judgment. It is largely superseded by modern, more precise nephelometric methods (see IS 3025 Part 10) that measure in NTU.

The method is not suitable for low turbidity water, such as potable water, as its lower detection limit of 25 JTU is well above the acceptable limits (typically < 1 NTU).

Proper maintenance is crucial; the bottom of the glass tube must be kept perfectly clean and unscratched, and the candle must be maintained at the correct height.