Scheele's Green
Encyclopedia
Scheele's Green, also called Schloss Green, is chemically a cupric
hydrogen arsenite
(also called copper arsenite or acidic copper arsenite), CuHAsO3. It is a compound similar to Paris Green
. It is a green pigment
, of yellowish hue and was used in the past in some paint
s but has since fallen out of use due to its toxicity.
Scheele's Green was invented in 1775 by Carl Wilhelm Scheele
. By the end of the 19th century, it virtually replaced the older green pigments based on copper carbonate.
Another method used to produce Scheele's green was by directly adding dilute copper sulphate solution to an alkali solution of arsenic. This would then precipitate—the precipitate also being Scheele's green.
It has been found that Scheele's green was composed of a variety of different compounds, including copper metaarsenite (CuO·As2O3), copper arsenite salt (CuAsHO3 and Cu(AsO3)2·3H2O)), neutral copper orthoarsenite (3CuO·As2O3·2H2O), copper arsenate (CuAsO2 and Cu(AsO2)2), copper diarsenite (2CuO·As2O3·2H2O).
Scheele's Green was more brilliant and durable than the then-used copper carbonate pigments. However it tended to fade and blacken when subjected to hydrogen sulfide
containing atmosphere. It also can not be mixed with pigments based on sulfide
s or containing sulfur.
Emerald green, also known as Paris Green
, was developed later in attempt to improve Scheele's Green. It had the same tendency to blacken, but was even more durable. By the end of 19th century, both greens were made obsolete by zinc oxide
and cobalt green
, also known as zinc green.
in 1930s, together with Paris Green. Scheele's Green can be used also to color wax candle
s.
Scheele's Green was used as a color for paper, e.g., for wallpapers and paper hangings, and in paints, even on some children's toys. It was also used to dye cotton and linen. The wallpapers containing Scheele's Green are implicated in the arsenic poisoning
of Napoleon Bonaparte. Tiny particles of the pigment tend to flake off and become airborne, and then are absorbed by the lungs. Also, when the wallpaper becomes damp and moldy, the pigment hydrolyzes and releases poisonous arsine containing gas.
Poisoning events due to this gas produced by certain microbes was assumed to be associated with the arsenic in paint in the late 19th century. In 1893 the Italian physician Bartolomeo Gosio published his results on "Gosio gas" that was subsequently shown to contain trimethylarsine
. Under wet conditions, the mold Scopulariopsis brevicaulis produces significant amounts of methyl arsines via methylation of arsenic-containing inorganic pigment
s, especially Paris green
and Scheele's Green, which were once used in indoor wallpapers. Newer studies show that trimethylarsine has a low toxicity and could therefore not account for the death and the severe health problems observed in the 19th century.
Arsenic poisoning was usually caused by the inhalation of arsine gas (AsH3), which can be released from compounds containing arsenic following certain chemical processes, such as heating, or its metabolism by an organism. Fungi such as Scopulariopsis or the Paecilomyces species release arsine gas, when they are growing on a substance containing arsenic. In these compounds, the Arsenic is either pentavalent or trivalent (arsenic is in group 15), depending on the compound. In humans, arsenic of these valences is readily absorbed by the gastrointestinal tract, which accounts for its high toxicity. Pentavalent arsenic tends to be reduced to trivalent arsenic and trivalent arsenic tends to proceed via oxidative methylation in which the trivalent arsenic is made into a mono, di and trimethylated products by the S adenosyl methionine (an enzyme) and its cofactor glutatione. Arsenic is not only toxic, but it also has carcinogenic effects.
Despite its high toxicity, Scheele's Green was also used as a food dye for sweets
such as green blancmange
, a fondness of traders in 19th century Greenock
, leading to a long-standing Scottish prejudice against green sweets. The presence of Scheele's Green as a colorant in absinthe
is now thought to be the source of the problems with the liquor that led to its banishment in most European countries and the US by 1915. Another popular poisonous colorant was chrome yellow
, used for sweets, snuff
and custard
powder. There is one example of an acute poisoning of children attending a Christmas party where such candles were burned.
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
hydrogen arsenite
Arsenite
In chemistry an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3.The different forms of the anion are the next ones:* ortho-arsenite: AsO33-* meta-arsenite: AsO2-...
(also called copper arsenite or acidic copper arsenite), CuHAsO3. It is a compound similar to Paris Green
Paris Green
Paris Green is an inorganic compound more precisely known as copper acetoarsenite. It is a highly toxic emerald-green crystalline powder that has been used as a rodenticide and insecticide, and also as a pigment, despite its toxicity. It is also used as a blue colorant for fireworks...
. It is a green pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
, of yellowish hue and was used in the past in some paint
Paint
Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...
s but has since fallen out of use due to its toxicity.
Scheele's Green was invented in 1775 by Carl Wilhelm Scheele
Carl Wilhelm Scheele
Carl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
. By the end of the 19th century, it virtually replaced the older green pigments based on copper carbonate.
Preparation
The pigment was originally prepared by making a solution of sodium carbonate at a temperature of around 90 °C, then slowly adding in arsenious oxide, while constantly stirring until everything had dissolved. This sodium arsenite solution was then added to a copper sulphate solution. The sodium would displace the copper, which resulted in the formation of the desired product in the form of a green precipitate. This copper arsenite was then filtered off and warmed to around 43 °C to dry the crystals. To enhance the color, the salt was subsequently heated to 60-70 °C. The intensity of the color depends on the copper : arsenic ratio, which in turn was affected by ratio of the starting materials, as well as the temperature.Another method used to produce Scheele's green was by directly adding dilute copper sulphate solution to an alkali solution of arsenic. This would then precipitate—the precipitate also being Scheele's green.
It has been found that Scheele's green was composed of a variety of different compounds, including copper metaarsenite (CuO·As2O3), copper arsenite salt (CuAsHO3 and Cu(AsO3)2·3H2O)), neutral copper orthoarsenite (3CuO·As2O3·2H2O), copper arsenate (CuAsO2 and Cu(AsO2)2), copper diarsenite (2CuO·As2O3·2H2O).
Scheele's Green was more brilliant and durable than the then-used copper carbonate pigments. However it tended to fade and blacken when subjected to hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
containing atmosphere. It also can not be mixed with pigments based on sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
s or containing sulfur.
Emerald green, also known as Paris Green
Paris Green
Paris Green is an inorganic compound more precisely known as copper acetoarsenite. It is a highly toxic emerald-green crystalline powder that has been used as a rodenticide and insecticide, and also as a pigment, despite its toxicity. It is also used as a blue colorant for fireworks...
, was developed later in attempt to improve Scheele's Green. It had the same tendency to blacken, but was even more durable. By the end of 19th century, both greens were made obsolete by zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...
and cobalt green
Cobalt green
Cobalt green, sometimes known as Rinman's green or Zinc Green, is a translucent green pigment made by heating a mixture of cobalt oxide and zinc oxide. Sven Rinman, a Swedish chemist, discovered this compound in 1780. Although it is stable and can be safely mixed with other pigments, it is rarely...
, also known as zinc green.
Uses
Scheele's Green was used as an insecticideInsecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
in 1930s, together with Paris Green. Scheele's Green can be used also to color wax candle
Candle
A candle is a solid block or cylinder of wax with an embedded wick, which is lit to provide light, and sometimes heat.Today, most candles are made from paraffin. Candles can also be made from beeswax, soy, other plant waxes, and tallow...
s.
Scheele's Green was used as a color for paper, e.g., for wallpapers and paper hangings, and in paints, even on some children's toys. It was also used to dye cotton and linen. The wallpapers containing Scheele's Green are implicated in the arsenic poisoning
Arsenic poisoning
Arsenic poisoning is a medical condition caused by increased levels of the element arsenic in the body. Arsenic interferes with cellular longevity by allosteric inhibition of an essential metabolic enzyme...
of Napoleon Bonaparte. Tiny particles of the pigment tend to flake off and become airborne, and then are absorbed by the lungs. Also, when the wallpaper becomes damp and moldy, the pigment hydrolyzes and releases poisonous arsine containing gas.
Poisoning events due to this gas produced by certain microbes was assumed to be associated with the arsenic in paint in the late 19th century. In 1893 the Italian physician Bartolomeo Gosio published his results on "Gosio gas" that was subsequently shown to contain trimethylarsine
Trimethylarsine
Trimethylarsine is the chemical compound with the formula 3As, commonly abbreviated AsMe3 or TMAs. This organic derivative of arsine has been used as a source of arsenic in microelectronics industry, a building block to other organoarsenic compounds, and serves as a ligand in coordination...
. Under wet conditions, the mold Scopulariopsis brevicaulis produces significant amounts of methyl arsines via methylation of arsenic-containing inorganic pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s, especially Paris green
Paris Green
Paris Green is an inorganic compound more precisely known as copper acetoarsenite. It is a highly toxic emerald-green crystalline powder that has been used as a rodenticide and insecticide, and also as a pigment, despite its toxicity. It is also used as a blue colorant for fireworks...
and Scheele's Green, which were once used in indoor wallpapers. Newer studies show that trimethylarsine has a low toxicity and could therefore not account for the death and the severe health problems observed in the 19th century.
Toxicity
Today it is intuitive to most that a complex containing arsenic is most likely to be toxic, but in the 19th century this was not readily known. 19th century journals reported of children wasting away in bright green rooms, of ladies in green dresses swooning and newspaper printers being overcome by arsenic vapors.Arsenic poisoning was usually caused by the inhalation of arsine gas (AsH3), which can be released from compounds containing arsenic following certain chemical processes, such as heating, or its metabolism by an organism. Fungi such as Scopulariopsis or the Paecilomyces species release arsine gas, when they are growing on a substance containing arsenic. In these compounds, the Arsenic is either pentavalent or trivalent (arsenic is in group 15), depending on the compound. In humans, arsenic of these valences is readily absorbed by the gastrointestinal tract, which accounts for its high toxicity. Pentavalent arsenic tends to be reduced to trivalent arsenic and trivalent arsenic tends to proceed via oxidative methylation in which the trivalent arsenic is made into a mono, di and trimethylated products by the S adenosyl methionine (an enzyme) and its cofactor glutatione. Arsenic is not only toxic, but it also has carcinogenic effects.
Despite its high toxicity, Scheele's Green was also used as a food dye for sweets
SweetS
was a Japanese idol group. Put together through auditions, the group debuted in 2003 on the avex trax label. Although the group met minor success, they disbanded after three years with the release of a final single in June 2006....
such as green blancmange
Blancmange
Blancmange is a sweet dessert commonly made with milk or cream and sugar thickened with gelatin, cornstarch or Irish moss, and often flavored with almonds. It is usually set in a mould and served cold. Although traditionally white, blancmanges are frequently given a pink color as well...
, a fondness of traders in 19th century Greenock
Greenock
Greenock is a town and administrative centre in the Inverclyde council area in United Kingdom, and a former burgh within the historic county of Renfrewshire, located in the west central Lowlands of Scotland...
, leading to a long-standing Scottish prejudice against green sweets. The presence of Scheele's Green as a colorant in absinthe
Absinthe
Absinthe is historically described as a distilled, highly alcoholic beverage. It is an anise-flavoured spirit derived from herbs, including the flowers and leaves of the herb Artemisia absinthium, commonly referred to as "grande wormwood", together with green anise and sweet fennel...
is now thought to be the source of the problems with the liquor that led to its banishment in most European countries and the US by 1915. Another popular poisonous colorant was chrome yellow
Chrome yellow
Chrome Yellow is a natural yellow pigment made of lead chromate . It was first extracted from the mineral crocoite by the French chemist Louis Vauquelin in 1809...
, used for sweets, snuff
Snuff
Snuff is a product made from ground or pulverised tobacco leaves. It is an example of smokeless tobacco. It originated in the Americas and was in common use in Europe by the 17th century...
and custard
Custard
Custard is a variety of culinary preparations based on a cooked mixture of milk or cream and egg yolk. Depending on how much egg or thickener is used, custard may vary in consistency from a thin pouring sauce , to a thick pastry cream used to fill éclairs. The most common custards are used as...
powder. There is one example of an acute poisoning of children attending a Christmas party where such candles were burned.