<P> The density of substances varies with temperature and pressure so that it is necessary to specify the temperatures and pressures at which the densities or masses were determined . It is nearly always the case that measurements are made at nominally 1 atmosphere ( 101.325 kPa the variations caused by changing weather patterns ) but as relative density usually refers to highly incompressible aqueous solutions or other incompressible substances ( such as petroleum products ) variations in density caused by pressure are usually neglected at least where apparent relative density is being measured . For true ( in vacuo ) relative density calculations air pressure must be considered ( see below ) . Temperatures are specified by the notation T / T ) with T representing the temperature at which the sample 's density was determined and T the temperature at which the reference ( water ) density is specified . For example , SG ( 20 ° C / 4 ° C ) would be understood to mean that the density of the sample was determined at 20 ° C and of the water at 4 ° C. Taking into account different sample and reference temperatures we note that while SG = 1.000000 ( 20 ° C / 20 ° C ) it is also the case that RD = 0.998203 / 0.998840 = 0.998363 ( 20 ° C / 4 ° C ) . Here temperature is being specified using the current ITS - 90 scale and the densities used here and in the rest of this article are based on that scale . On the previous IPTS - 68 scale the densities at 20 ° C and 4 ° C are , respectively , 0.9982071 and 0.9999720 resulting in an RD ( 20 ° C / 4 ° C ) value for water of 0.9982343 . </P>
<P> The density of substances varies with temperature and pressure so that it is necessary to specify the temperatures and pressures at which the densities or masses were determined . It is nearly always the case that measurements are made at nominally 1 atmosphere ( 101.325 kPa the variations caused by changing weather patterns ) but as relative density usually refers to highly incompressible aqueous solutions or other incompressible substances ( such as petroleum products ) variations in density caused by pressure are usually neglected at least where apparent relative density is being measured . For true ( in vacuo ) relative density calculations air pressure must be considered ( see below ) . Temperatures are specified by the notation T / T ) with T representing the temperature at which the sample 's density was determined and T the temperature at which the reference ( water ) density is specified . For example , SG ( 20 ° C / 4 ° C ) would be understood to mean that the density of the sample was determined at 20 ° C and of the water at 4 ° C. Taking into account different sample and reference temperatures we note that while SG = 1.000000 ( 20 ° C / 20 ° C ) it is also the case that RD = 0.998203 / 0.998840 = 0.998363 ( 20 ° C / 4 ° C ) . Here temperature is being specified using the current ITS - 90 scale and the densities used here and in the rest of this article are based on that scale . On the previous IPTS - 68 scale the densities at 20 ° C and 4 ° C are , respectively , 0.9982071 and 0.9999720 resulting in an RD ( 20 ° C / 4 ° C ) value for water of 0.9982343 . </P>
what is the value of relative density of water
what is the value of relative density of water
0.9982343
0.9982343