text: Joseph Priestley, in Observations on different kinds of air, was one of the first people to describe air as being composed of different states of matter, and not as one element.  Priestley elaborated on the notions of fixed air (CO), mephitic air and inflammable air to include "inflammable nitrous air," "vitriolic acid air," "alkaline air" and "dephlogisticated air". Priestley also described the process of respiration in terms of phlogiston theory. Priestley also established a process for treating scurvy and other ailments using fixed air in his Directions for impregnating water with fixed air. Priestley's work on pneumatic chemistry had an influence on his natural world views. His belief in an "aerial economy" stemmed from his belief in "dephlogisticated air" being the purest type of air and that phlogiston and combustion were at the heart of nature. 
  Joseph Priestley chiefly researched with the pneumatic trough, but he was responsible for collecting several new water-soluble airs. This was achieved primarily by his substitution of mercury for water, and implementing a shelf under the head for increased stability, capitalizing on the idea Cavendish proposed and popularizing the mercury pneumatic trough.