Red calx of mercury

The first day of August in the year 1774 is one of the most memorable dates in the history of science, and, indeed (although unknown to most historians), in the history of civilisation. On that sunny day, at Bowood near Caine in Wiltshire, where Priestley held the post of librarian and literary companion to Lord Shelburne, he focused his new glass upon some red calx of mercury, or mmurius calcinatus... 

The theoretical interpretation of this experiment was a tricky business. Priestley later recognized that the red calx of mercury upon heating actually emitted... 

The French scientist Antoine Lavoisier (1743-1794) was one of the first to use an analytical balance like the one shown in Figure 3-10 to monitor chemical reactions. He studied the thermal decomposition of mercury(II) oxide, known then as calx of mercury. Mercury(II) oxide is a powdery red solid. When it is heated, the red solid reacts to form silvery liquid mercury and colorless oxygen gas as shown in Figure 3-11 on the next page. The color change and production of a gas are indicators of a... 

He admitted that Lavoisier s experiments proved that pure air or dephlogisti-cated air (oxygen) is fixed in combustions and in calcination of metals, but he supposed also that phlogiston, which is the matter of light, is at the same time emitted. The reason why calx of mercury (red precipitate) is reduced at a red heat without the addition of phlogistic material such as charcoal is that phlogiston is ... 

The alchemists viewed arsenic as a bastard metal or semi-metal . Some regarded it as akin to quicksilver, its red sulphide resembling cinnabar, and the volatility of its compounds that of mercury salts. To it they gave the symbol o—o often accompanied by a coiled snake. Brandt observed that white arsenic, AsjOs, was the calx of the semi-metal. 

He heated 4 oz. of mercury in a retort which communicated with a measured volume of air in a bell-jar over mercury (Fig. 38). The volume of air in the bell and in the retort was 50 cu. in. After a time he noticed the formation of red specks and scales of calx on the surface of the mercury. After twelve days the scales no longer increased the fire was removed, and the experiment stopped. The air had contracted to 42 cu. in., and the gas left was mephitic air mofette). The scales, or mercury calx mercurius calcinatm per e), were collected and found to weigh 45 grains. They were transferred to a small retort and heated 8 to 9 cu. in. of the salubrious part of the air , or respirable air, were obtained, together with 41 grains of mercury. When this respirable air was added to the atmospheric mofette, ordinary air was formed. 

Gren and Westrumb reported that water is formed when red or black (mercurous oxide ) precipitate of mercury is reduced by heating, which Girtanner said was formed by the burning of organic dust from the atmosphere which had settled on the calx. 

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