Scheele Green , also called Schloss Green , is chemically a copper hydrogen arsenite (also called copper arsenite or acid copper arsenite ), CuHAsO
3 . Chemically linked to Paris Green. It is a yellowish green pigment that was in the past used in some paint, but has since not been used because of its toxicity and color instability in the presence of sulphides and various chemical pollutants.
Scheele Green was discovered in 1775 by Carl Wilhelm Scheele. At the end of the 19th century, it almost replaced the older green pigments based on copper carbonate.
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The pigment was originally prepared by making a sodium carbonate solution at a temperature of about 90 ° C, then slowly adding arsenious oxide, while continuously stirring until it dissolves. This results in a solution of sodium arsenite. Added to a solution of copper sulphate, resulting in a green precipitate of insoluble copper arsenite effectively. After filtration, the product is dried around 43 ° C. To increase the color, the salt is then heated to 60-70 ° C. The color intensity depends on the ratio of copper: arsenic, which in turn is affected by the ratio of the starting material, as well as the temperature.
It has been found that Scheele green is made up of a variety of different compounds, including copper metaarsenite ( CuOÃ, Â · As
2 O
3 ), copper arsenite salt ( CuHAsO
3 and Cu (AsO
3 )
2 Ã, Â · 3H
2 O) ), neutral copper orthoarsenite ( 3CuOÃ, Â · As
2 O
3 Ã, Â · 2H
2 O ), copper arsenate ( CuAsO
2 and Cu (AsO
2 )
2 ), and copper diarsenite ( 2CuOÃ, Â · As
2 O
3 Ã, Â · 2H
2 O ).
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Usage
Scheele Green is used as a color for paper, for example for wallpaper and paper decoration, and in paint, candle wax, and even on some children's toys. It is also used for dyeing cotton and linen. Green Scheele is more brilliant and durable than copper carbonate pigments used. However, because the copper content tends to fade and blacken when exposed to sulfides, either in the form of atmospheric hydrogen sulfide or in a pigment mixture based on or containing sulfur.
The green emerald, also known as Paris Green, was developed later in an effort to improve Green Scheele. It has the same tendency to blacken, but it is more durable. At the end of the 19th century, both green became obsolete by cobalt green, also known as green zinc, which is much less nontoxic.
Scheele Green was used as an insecticide in the 1930s, along with Paris Green.
Despite high toxicity evidence, Scheele Green is also used as a food dye for candies such as green blancmange, a trader's delight in Greenock of the 19th century; this led to longstanding Scottish prejudice against green candy.
Toxicity
In the 19th century, the toxicity of arsenic compounds was not easily known. The nineteenth-century journals contained reports of children splitting up in bright green rooms, women in faint green clothes and newspaper printers being overcome by arsenic vapors. There is an example of acute poisoning of children attending a Christmas party where the colored candles are burned.
Two main theories about the cause of wallpaper poisoning events have been proposed: dust particles caused by pigment and paper peeling, and toxic gas production. The tiny particles of the pigment can peel and become air, and then absorbed by the lungs. Alternatively, toxic gases can be released from compounds containing arsenic after certain chemical processes, such as heating, or metabolism by organisms. When the wallpaper becomes damp and moldy, the pigment may be metabolized, causing the release of arsenine gas toxic ( AsH
3 ). Fungi genera such as Scopulariopsis or Paecilomyces release arsine gas, as they grow on arsenic-containing substances. Italian physician Bartolomeo Gosio published in 1893 the results of "Gosio gas", which later proved to contain trimethylarsine. In wet conditions, the fungus Scopulariopsis brevicaulis produces large amounts of methyl arsine through the methylation of inorganic pigments containing arsenic, especially green Paris and Scheele Green.
In this compound, arsenic is either pentavalent or trivalent (arsenic in group 15), depending on the compound. In humans, arsenic from this valency is readily absorbed by the gastrointestinal tract, which is responsible for its high toxicity. Pentavalent arsenic tends to be reduced to trivalent arsenic and trivalent arsenic tends to continue through oxidation methylation where trivalent arsenic is made into mono, di and trimethylation products by methyltransferasease and methylene S-adenosyl methylene supply cofactors. However, more recent studies show that trimethylarsine has a low toxicity, and therefore can not account for the deaths and severe health problems observed in the 19th century.
Arsenic is not only toxic, but also has a carcinogenic effect.
Role in Napoleon's death
During Napoleon's exile at St. Helena, she lives in a house where the room is painted a bright green, her favorite color. The cause of his death is generally believed to be stomach cancer, and arsenic exposure has been linked to an increased risk of stomach cancer. Analysis of her hair samples showed a large amount of arsenic. Because St. Helena has a rather humid climate, like mushrooms growing on the walls. It has also been suggested that the presence of such high levels of arsenic may be due to the effort to preserve the body.
See also
- Do not be confused with copper arsenate
- List of inorganic pigments
References
External links
- Case Study in Environmental Medicine - Arsenic Poisoning
- National Pollutant Inventory - Copper and compound fact sheet
- Napoleon Toxic Wallpaper
Source of the article : Wikipedia
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