The Application of Radiant Heating in the Clinical Laboratory

Since Priestley utilized the radiant energy of the sun with his burning glass in his famous experiment of 1774, the method has fallen into disuse and the chemist has accepted the water-bath, the hot-air oven, and the furnace as the standard tools for evaporation, drying, and combustion. The boiling water-bath is used for evaporating solutions or drying solids which decompose at temperatures slightly above 1000 C. It is slow; it wastes nearly all of the energy used; it requires a constant supply of cold water and a constant overflow into a sink; and steam condenses on every available cold surface and helps metals to corrode or wood to rot. If it is used for evaporating volatile solvents, they readily superheat so that loss is often caused by bumping. If gas heating is used for evaporating inflammable solvents, there is a serious hazard of fire, while electrically heated baths have a fairly short life and are expensive. Drying ovens, often jacketed by steam or toluene vapour, are inefficient because they depend on conduction and convection to transfer heat from the walls of the chamber to an object which is maintained at almost the same temperature. Provision for the removal of vapour is rarely adequate, and the ovens corrode rapidly. Many of the objections to the drying oven apply to the furnace, but since the furnace is usually well lagged it is more efficient. The main disadvantages are its bulk, high cost, and high energy consumption. Radiant energy is widely used in industry. It travels in straight lines and is converted into heat when it strikes and is absorbed by an object. We have used it to evaporate to dryness aqueous solutions; to evaporate inflammable solvents; to dry solids without overheating; and to ash stools and other organic material. We have found that our methods employing radiant energy are cheaper, quicker, and more convenient than the conventional methods. In particular, in dealing with