**Calculation of density from relative density**

Suppose we have measured the relative density of a liquid as described above and found it to be 0.8. If we now assume that 1 cm ‘ of water has a mass of 1 g, it follows that the mass of any volume of water is numerically the same as its volume in cm ‘.

Consequently, we can say straight away that the density of our liquid is 0.8 g/cm3. However, a word of warning is necessary. To say that I cm ‘ of water has a mass of I g, is only a very close approximation. Owing to expansion, the density of water depends on its temperature. In work of very high accuracy, scientists make due allowance for this when calculating

density from relative density. Other corrections also have to be made concerned with the weighing process, but any further discussion would take us into the realm of more advanced studies.

Finally, it is worth noting that the figures expressing the density of a substance depend on the units used. For example, the density of lead is II 400 kg/rn ‘ or 11.4 g/cm3, but its density relative to water is a number or ratio, namely, 11.4 and this is the same whatever system of units is used.

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