Manufacturer and builder 3, 1871
There is a class of bright green paints in the trade, which are all a combination of copper and arsenic, with some lime, potash, etc., in different proportions, and which, chemically considered, should bear the name of arsenite of copper; in time common language of the trade they bear different names in different localities, and these are still more varied by their shade of color, which often depends on a trifle during time preparation. Besides the names mentioned at time head of this article, which are time most common in this part of time world, they are called Schweinfurter green, after the German city where it was first manufactured; Scheele's green, after the eminent chemist who first discovered it; Saalfeld, Vienna, Cassel green, after different cities from whence it may be obtained; new green, as once it was a novelty; kaiser, or imperial green, as it is time most brilliant of all greens; in fact, there exists time greatest confusion imaginable in regard to time names given to these paints. All differ slightly, and ought only to be judged by close inspection.
The original green as made by Scheele, in Sweden, comes into time trade in broad, irregular tabular pieces, but differs in tone from bright green to a very deep color. The fracture is conchoidal, (like a shell,) and possesses in time darker varieties a beautiful brown lustre. It is very brittle, and when powdered much lighter in color. In manufacturing the different shades, there is no difference in time method except in the quantity of arsenic, a larger proportion of which makes it lighter, until finally, by excess of arsenic, it becomes yellowish green. As the copper paints are naturally bluish-green, it is seen that the arsenic counteracts this, as it has a tendency to make yellow compounds - for instance, orpiment, which is a com-pound of arsenic and sulphur.
To make Paris green, take 10 parts cupric sulphate, (blue vitriol,) dissolve in about 50 parts water, let the solution settle till clear, and draw it off into a vessel which has previously been filled with about 100 parts of water.
Then take 9 parts of pure calcined potash, and 5 parts of quicklime, and make a caustic lye of time strength of about 15° to 20° of time hydrometer; separate the clear solution from time deposit of lime.
Then take 1 part arsenious acid, and 2 parts calcined potash, dissolve them together with sufficient water, by boiling in a copper vessel, let it settle, and pour off time clear liquid.
Then pour time arsenic solution in that of the cupric sulphate, stir well, and add the caustic lye; a precipitate will be formed, which is the paint desired, and which by washing is purified from the adhering caustic liquid. This washing must be repeated three to six times; then time precipitate is dried in a warm place upon linen filters, in layers of less than half an inch thick, which are afterward pressed. Warmth improves the appearance and lustre.
We suggest that soda, and even the crystallized carbonate, or so-called washing-soda, which is at present so cheap in this country, may be used in place of time potash. Fourteen parts of time same may supplant the nine parts of potash mentioned, the same amount of lime to be used.
From the amount of ingredients mentioned, we obtain about 5 parts dry paint. It is seldom adulterated, as it can not stand it. It loses its lustre and peculiar fracture by time addition of white; also it is very difficult to divide the white adulteration so well that it can not be seen on the fracture. The only adulteration possible is with barytic-sulphate, (heavy spar;) and this is easily found by dissolving time paint in nitric acid, when the heavy spar will remain undissolved. When it is required to ascertain the amount of the adulteration, time spar must be digested with liquid ammonia, to purify it, then dried and weighed.
This paint is the original Scheele's green, and so, called in Sweden; but what at the present day is called in Germany and the United States Scheele's green, is made by simply dissolving, in a solution of 9 parts calcined potash, about 3 to 4 parts of arsenic, more or less according to tint desired, and throwing it in a boiling solution of 10 parts of cupric-sulphate, which must contain no iron. After stirring well, it is left to settle, and the precipitate is washed and dried. It is used as a water-color, oil-color, and as a lime-color.