198 THE ATMOSPHERE 



ing of copper and gold ornaments 6000-7000 years ago. The 

 energy of the alchemist, misdirected in pursuit of the transmuta- 

 tion of metals, was wasted owing to the neglect of accurate 

 measurement and weighing of the substances used in and the 

 products obtained by their manipulations. " If," says Scheele in 

 1777, "the chemists of the preceding century had thought 

 worthy of a more particular examination the elastic fluids 

 resembling air which manifest themselves in so many operations, 

 how advanced should we now be ! They desired to see every- 

 thing in corporeal form, and to collect everything as drops in 

 the receiver." 



Leonardo da Vinci, who followed the pursuit of science with no 

 less genius than that of art, observed that fire robbed air of its life- 

 sustaining property. Van Helmont (15571664) separated a gas 

 which was given off by the action of vinegar on shell, by burning 

 wood and by fermentation, a gas which would not support life 

 in fact, carbonic acid gas. Mayow (16461679) recognised that 

 there was in the atmosphere an essential part, active in supporting 

 combustion, in calcining metals, in changing venous to arterial 

 blood, and in sustaining fermentation. He determined that con- 

 fined air loses its power to support combustion and life. Mayow, 

 in fact, discovered oxygen under the name " spiritus nitro-a3rius," 

 but his experiments attracted little notice and were soon forgotten. 

 Boyle (1624-1694) demonstrated to the newly-founded Royal 

 Society the death of animals placed in the evacuated receiver of 

 his celebrated air-pump, and recognised that the air must be 

 renewed in sustaining life by artificial respiration. Bernouilli 

 found that fish could not live in boiled (gas-free) water. Lower 

 (1669) observed the colour change of venous into arterial blood 

 during the artificial respiration of an animal. Joseph Black 

 (1757), by his admirable researches on the analysis and synthesis 

 of chalk, separated " fixed air " (carbonic acid), and studied the 

 properties of this gas. In 1772, Scheele, a poor Swedish 

 apothecary, " put an ounce of purified nitre in a glass retort for 

 distillation, and made use of a bladder, moistened and emptied 

 of air, in place of a receiver. As soon as the nitre began to glow 

 it also began to boil, and at the same time the bladder was 

 expanded by the " fire-air " (oxygen) that passed over. In 

 1774, Priestley, an eminent Unitarian minister of Birmingham, 



1 Perkin and Lean, " Introduction to Chemistry and Physics." 



