THE DISCOVERY OF GASES - Sceele 4#

Sceele

Carl Wilhelm Scheele was born in 1742 at Stralsund. He received little schooling and was apprenticed to an aphotecary in Gotenburg when he was 14 years old. Scheele was a man of great modesty and his circumstances were often poor. He worked with very simple apparatus and in periods of scanty leisure, in a cold and uncomfortable laboratory, yet he made a great number of chemical discoveries.

Figure 18. Carl Wilhelm Scheele (1742 – 1786)

In 1777, Scheele published his only book, Chemische Abhandlung von der Luft und dem Feur (Chemical Observations and Experiments on Air and Fire). In this work, he stated that “the air is composed of two fluids (gases), one supporting combustion, which he named “Fire air” and the other preventing it, which he named “Foul air” : they were afterwards named Oxygen and Nitrogen, respectively.

Scheele burned a hydrogen flame under a glass globe standing over water. The water at once began to rise, until it filled one-fourth of the flask, when the flame went out. He assumed that the inflammable substance (hydrogen) had combined with the fire air, and since he was unable to find the product of the combination (Note : he missed the dew deposited on the flask, since he used hot water), he assumed that it was “heat” which had escaped through the glass.

heat = fire air + φ

He therefore tried to decomposed heat and set free the fire air by several methods and in this way he made an imense step forward.

Scheele prepared “fire air” in several ways. He heated calx of mercury (mercuric oxide), which he supposed absorbed phlogiston from the heat, setting free the fire air.

calx of mercury + (φ + fire air) = (calx of mercury + φ) + fire air

heat mercury

Figure 19. Scheele’s isolation of fire air.

He also obtained fire air by heating “black manganese” (manganese dioxide) with sulphuric acid or arsenic acid; by strongly heating nitre alone; by heating mercurous and mercuric nitrates and by heating silver or mercurous carbonate, the aerial acid (carbon dioxide) simultaneously produced being absorbed by bringing the gas in contact with an alkali.