by plant leaves exposed to sunlight were oxygen bubbles. His description of photosynthesis was published in 1779, and in 1785 he wrote about eudiometers in Journal de Physique (v 26, p 339). According to a biographer, Ingenhousz indicated that "many instruments were called eudiometers although strictly speaking they didn't deserve the name ... misunderstandings could exist when not everybody was using the same instruments." An electrified version of the eudiometer was developed by Count Alessandro Volta (1745–1827), an Italian physicist who is well known for his contributions to the electric battery and electricity. Aside from its laboratory function, the eudiometer is also known for its part in the "Volta pistol". Volta invented this instrument in 1777 for the purpose of testing the "goodness" of air, analyzing the flammability of gases, or to demonstrate the chemical effects of electricity. Volta's Pistol had a long glass tube that was closed at the top, like a eudiometer. Two electrodes were fed through the tube and produced a spark gap inside the tube. Volta's initial use of this instrument concerned the study of swamp gases in particular. Volta's pistol was filled with oxygen and another gas. The homogeneous mixture was taped shut with a cork. A spark could be introduced into the gas chamber by electrodes, and possibly catalyze a reaction by static electricity, using Volta's electrophorus. If the gases were flammable, they would explode, and increase the pressure within the gas chamber. This pressure would be too great and eventually cause the cork to become airborne. Volta's pistol was made with either glass or brass, however due to the electricity the glass was vulnerable to exploding. Volta's extensive studies on measuring and creating high levels of electric currents caused the electrical unit, the volt, to be named after him. In 1785 Henry Cavendish used a eudiometer to determine the fraction of oxygen in the Earth's atmosphere. Etymology The name "eudiometer" comes from the Greek meaning clear or mild, which is the combination of the prefix meaning "good", and meaning "heavenly" or "of Zeus" (the god of the sky and atmosphere), with the suffix -meter meaning "measure". Because the eudiometer was originally used to measure the amount of oxygen in the air, which was thought to be greater in "nice" weather, the root appropriately describes the apparatus. Usage Applications of a eudiometer include the analysis of gases and the determination of volume differences in