Physical-chemical Testing studies

The physical state, color and the odour at 20 °C of the test item will be described by conventional terms.

The transition from solid to liquid phase takes place over temperature range. Therefore, the term "melting range" is often used and, in practice, the temperatures of the initial and final stages of melting are determined. For freezing Point, A sample of the substance is placed in a test tube and stirred continuously. As the sample is cooled, its temperature is measured at regular intervals. As soon as the temperature remains constant for a few readings (corrected for thermometer error), this temperature is recorded as the freezing temperature.

A sample is heated gradually in boiling test tube which is immersed in a liquid bath. The sample tube is held in close contact with a thermometer and it contains a boiling capillary which is fused about 1cm above its lower end. Upon approach of the boiling temperature bubbles emerge rapidly from the lower open end of the capillary. The boiling temperature is that temperature at which, at momentary cooling, the string of bubbles stops, and liquid suddenly rises in the capillary.

This guideline addresses the determination of the solubility in water of essentially pure substances which are stable in water and not volatile. The water solubility of a substance can be considerably affected by the presence of impurities. Before determining water solubility, it is useful to have some preliminary information on the substance, like structural formula, vapour pressure, dissociation constant and hydrolysis as a function of pH. Two methods, the column elution method and the flask method are used to determine solubility.

The density is calculated from the difference in weight between the full and empty pycnometer and its volume. For bulk density, a known weight of solid material is placed in a glass measuring cylinder and its volume is measured to determine pour density.Tap density is obtain by mechanically tapping in graduated measuring cylinder containing solid sample.

The purpose of the study is to evaluate the surface tension of an aqueous solution by means of a ring tensiometer at 20 °C. The methods are based on the measurement of the force which it is necessary to exert vertically on a stirrup or ring, in contact with the surface of the liquid, in order to separate it from the surface, or on a plate, with an edge in contact with the surface, in order to draw up the film that has formed.

The guideline describes a relatively quick method of estimating the octanol-water partition coefficient (log P_ow) of a test item by employing high performance liquid chromatography (HPLC). The reverse phase HPLC technique uses analytical columns filled with silica phase grafted with long hydrocarbon chains. The chemicals are thus retained in the column in proportion to their hydrocarbon/water partition coefficient. The log P_ow is determined from a correlation between the retention time (specifically, “log k,” or, ”capacity factor”) and the known log P_ow for a series of reference substances. The n-octanol/water partition ratio or coefficient is a key parameter in environmental risk assessment of chemicals and is used in a variety of calculations and models to estimate the environmental fate and bioavailability (and thus exposure) and toxicity of a test item.

This test guideline describes the procedure for the electrometric determination of pH of an undiluted aqueous solution or dispersion; the pH of 1% (w/v) dilution of a solution or dispersion in distilled or de-ionised water; or the pH of a chemical, diluted to end-use concentration.

“Flash point” is the minimum temperature at which a liquid gives off vapor within a test vessel in sufficient concentration to form an ignitable mixture with the air near the surface of the liquid. The lower the flash point, the easier it is to ignite a liquid solvent. These test method are applicable for the detection of contamination of relatively nonvolatile or nonflammable materials with volatile or flammable materials. These test methods should be used to measure and describe the properties of materials, products, or assemblies in response to heat and an ignition source under controlled laboratory conditions.

The test procedure is applicable to solid or liquid substances, which, in small amounts, will ignite spontaneously for a short time after coming into contact with air at room temperature .this is useful to determine explosive properties of the test item.