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who, in 1788, first made a solution of "chloride of lime." Later lo developed a solid powder. The chloride of lime bleached cloth in a few hours and accomplished what bleaching in the sun's rays could only do in months. In 1797 Tennant set up a chemical works in St. Rollox, Glasgow, and in 1799 he received a patent for making solid chloride of lime, to which he gave the name "bleaching powder." This so revolutionized the textile industry that bleaching powder became an important article, and considerable hydrochloric acid froin the LeBlanc process was converted into chlorine for the manufacture of bleaching powder.

In the LeBlanc process the black ash, after leaching, left a residue known as "tank waste." The waste began to accumulate so fast (about 1 1/2 tons for every ton of soda ash made) that its disposal became a serious problem. Here came Dr. Ludwig Mond (1862), who made use of air oxidation to free the sulfur. This is Mond's process for the recovery of sulfur from tank waste. The name of Mond is, however, usually associated with the development of the ammonia soda industry in England, though he was originally one of the LeBlanc soda men. His work in the development of the ammonia soda industry has overshadowed all this. At the same time another promising process was proposed by Schaffuer, who used magnesium chloride in conjunction with air:

$2CaS+2MgCl_{2}+O_{2}\rightarrow 2CaCl_{2}+2MgO+S_{2}$

The one process that was used successfully on an extensive scale, however, is that known after its inventors as the Chance-Claus process. In this process the waste was treated with carbon dioxide gas in a battery of carbonators whereby liydrogen sulfide gas was liberated and calcium sulfide transformed into calcium carbonate according to the following reactions:

$CaS+CO_{2}+H_{2}O\rightarrow CaCO_{2}+H_{2}S$

$CaS+H_{2}S\rightarrow Ca(HS)_{2}$

$Ca(HS)_{2}+CO_{2}+H_{2}O\rightarrow CaCO_{2}+2H_{2}S$

The hydrogen sulfide gas was burned to free sulfur by means of a carefully regulated supply of air in the presence of hydrated iron ore (ferric oxide) as a catalyst, thus:

$2H_{2}S+O_{2}\rightarrow 2H_{2}O+S_{2}$

The sulfur reclaimed from the tank waste is in a very pure form. It is thus possible to reclaim from the crude sulfur originally present in the pyrites that went to make sulfuric acid, pure free sulfur, commanding a good price on the market.

In connection with the burning of pyrites for sulfur dioxide gas, an iron oxide rich in copper resulted. Longmaid and Henderson devised a method of extracting copper from it by calcining it with salt, leaching out the copper chloride, and precipitating copper with iron scrap. This is known as the Longinaid and Henderson Wet Copper Process.