Requirements for equipment for Jackson candle turbidimeter and determination of turbidity
1981 Edition

The standard candle must be composed of paraffin wax or beeswax blended with spermaceti, having a congealing temperature between 58 and 60°C. It should have a uniform diameter of 20 mm and a length of 150 mm at the start. The candle's burn rate is specified between 7.39 and 8.16 grams per hour (114 to 126 grains per hour). The flame must burn clearly, white, without smoke or odor, and maintain a steady height and position. The candle is held against the top of the holder by a helical compression spring made from spring steel adhering to IS:4454 Part I standards, positioned so that the top of the candle holder is 76 mm below the bottom of the glass turbidity tube. The wick should be trimmed before each lighting to ensure consistent flame characteristics.

The turbidity tube used in the Jackson candle turbidimeter is internally 25 mm in diameter and varies in length from 250 mm to 760 mm depending on the turbidity range to be measured. It is graduated in 1 mm increments from 0 to 760 mm (or 76 cm), correlating to turbidity values ranging between 25 and 1000 turbidity units. The tube is made of transparent, colorless, optically clear natural glass with a flat, polished, and parallel bottom free from scratches, spots, or distortions to ensure accurate light transmission. It is encased within an annular brass tube coated with chromium plating to block extraneous light. For longer tubes, an extension annular brass tube is used to maintain the assembly's integrity and calibration.

To prepare the stock turbidity suspension (400 NTU), mix 5.0 ml each of Solution I and Solution II in a 100 ml volumetric flask. Allow the mixture to stand undisturbed for 24 hours at a temperature of 25 ± 3°C. After settling, dilute the mixture to the 100 ml mark with turbidity-free water and mix thoroughly. To create the standard turbidity suspension (40 NTU), dilute 10 ml of the stock suspension to 100 ml with turbidity-free water. For turbidity comparisons in the range of 5 to 100 JTU, prepare further dilutions of the stock suspension with turbidity-free water and place these along with the samples in identical bottles with sufficient headspace to allow shaking. Prior to measurement, shake the bottles and compare visually by observing a fixed background through the bottles under diffused lighting, recording the turbidity as that of the closest matching standard.

The Jackson candle turbidimeter assesses turbidity by visually observing the visibility of a standard candle flame through a water sample. As turbidity increases, particles scatter light, causing the flame to become progressively obscured. Turbidity is quantified in Jackson Turbidity Units (JTU). The instrument provides direct measurement within the range of 25 to 1000 JTU. For samples exhibiting turbidity above 1000 JTU, dilution with turbidity-free water is necessary to bring the turbidity within measurable limits. For turbidity values below 25 JTU, alternative indirect measurement methods are employed.

For samples with turbidity exceeding 1000 JTU, it is advised to dilute the original sample with turbidity-free water until the turbidity falls below 1000 JTU. The turbidity of this diluted sample is then measured using the Jackson candle turbidimeter. To calculate the original turbidity, multiply the measured turbidity of the diluted sample by the dilution factor, which is the total volume (sample plus diluent) divided by the volume of the original sample. For example, if one volume of sample is diluted with five volumes of water and the diluted turbidity measures 500 JTU, the original turbidity is calculated as 500 × (1+5) = 3000 JTU. This procedure ensures accurate turbidity determination beyond the direct measurement range of the instrument.