Black, an 18th-century medical doctor and professor of medicine at Glasgow University. He measured the specific heat capacities of many substances, using the term capacity for heat. Definition The specific heat capacity of a substance, usually denoted by or , is the heat capacity of a sample of the substance, divided by the mass of the sample: where represents the amount of heat needed to uniformly raise the temperature of the sample by a small increment . Like the heat capacity of an object, the specific heat capacity of a substance may vary, sometimes substantially, depending on the starting temperature of the sample and the pressure applied to it. Therefore, it should be considered a function of those two variables. These parameters are usually specified when giving the specific heat capacity of a substance. For example, "Water (liquid): = 4187 J⋅kg−1⋅K−1 (15 °C)" When not specified, published values of the specific heat capacity generally are valid for some standard conditions for temperature and pressure. However, the dependency of on starting temperature and pressure can often be ignored in practical contexts, e.g. when working in narrow ranges of those variables. In those contexts one usually omits the qualifier , and approximates the specific heat capacity by a constant suitable for those ranges. Specific heat capacity is an intensive property of a substance, an intrinsic characteristic that does not depend on the size or shape of the amount in consideration. (The qualifier "specific" in front of an extensive property often indicates an intensive property derived from it.) Variations The injection of heat energy into a substance, besides raising its temperature, usually causes an increase in its volume and/or its pressure, depending on how the sample is confined. The choice made about the latter affects the measured specific heat capacity, even for the same starting pressure and starting temperature . Two particular choices are widely used: If the pressure is kept constant (for instance, at the ambient atmospheric pressure), and the sample is allowed to expand, the expansion generates work as the force from the pressure displaces the enclosure or the surrounding fluid. That work must come from the heat energy provided. The specific heat capacity thus obtained is said to be measured at constant pressure (or isobaric), and is often denoted etc. On the other hand, if the expansion is prevented — for example by a sufficiently rigid enclosure, or by increasing