The solubility of any substance is a function of temperature. Most substances are endothermic, absorbing heat in the process of dissolution. For these substances, an increase in temperature results in an increase in solubility. A few substances, such as calcium hydroxide and sodium carbenicillin, are exothermic and give off heat in the process of dissolution. The solubility of such substances would decrease with an increase in temperature. The application of this aspect of solubility is of limited use to us, since pharmaceutical solutions must be administered at or near room or body temperature. It is more a factor to be considered for product storage than for formulation.