PROCEDURE

Heat the clean evaporating dish 180c for 1 hour. Cool, desiccate, weigh and store in desiccators until ready for use. Select the volume of the sample which has residue between 25 and 250 mg, preferably between 100 and 200 mg. this volume may be estimated from values of specific conductance. To obtain a measurable residue, successive aliquots of sample may be added to the sample dish.

Pipette this volume in a weight evaporating dish on steam bath. Evaporation may also be performed in a drying oven. The temperature shall be lowered to approximately 98c to prevent boiling and splattering of the sample. After complete evaporation of water from the residue, transfer the dish to an oven at 103-105c or 179-181c and dry to constant mass, that is, till the difference in the successive weightings is less than 0.5 mg. drying for a long duration is done to eliminate necessity of checking for constant mass. The time for drying to constant mass with a given type of sample when a number of samples of nearly same type are to be analyzed, has to be determined by trail.

Weight the dish as soon as it has cooled avoiding residue to stay for long time as some residues are hygroscopic and may absorb water from desiccant that is absolutely dry.

After weighting, ignite the dish in a muffle furnace at 550c for 1 hour. After ignition, allow the vessel to partially cool in air and transfer to desiccators, cool and weight.

Uses: This test is used for to find the Inorganic solids of water in mg/l.