Manufacturer and builder 6, 1871
In certain localities, a blue vitriol free from iron, and also vinegar, acetate of lime, or acetate of soda, may be obtained at such a low figure that it is much more economical to manufacture green colors from these ingredients than front verdigris. The details of the operation are as follows
1. With acetate of soda.
In place of 100 lbs. dis-tilled verdigris, take a solution of 136 lbs. crystallized acetate of soda, and 125 lbs. pure blue vitriol, free from iron. The mutual decomposition produces 100 parts of acetate of copper and 161 parts of sulphate of soda, which latter does not interfere in the least with the formation of the color. The remainder of the operation is the same as that explained for the Schweinfurter green, (page 98.)
2. With acetate of lime.
This acetate must be the pure, dry acetate, and not the dirty compound obtained by the distillation of wood. If dry, 80 pounds, and more when moist, are dissolved in about 150 pounds of water. Then 125 pounds of blue vitriol are dis-solved in about 500 pounds of water, and boiled. The solutions are allowed to cool a little, and the former is then poured slowly into the latter, as long as precipitate takes place. All, or nearly all, the acetate is required; what remains is used for the next operation. The precipitate (sulphate of lime) is separated by filtration, while the liquid, containing the acetate of copper (verdigris) in solution, is placed in the copper boiler. The precipitate is washed repeatedly, in order not to lose the adherent verdigris, and the wash-water is used for future solutions, in place of water. However, there always remains, adhering to the precipitate, some basic, less soluble acetate of copper, which can not well be washed out. It is usually preferred, therefore, to change the acetate of lime first into acetate of soda, by mixing the solution of about 80 pounds of acetate of lime, already descrioioed, with one of 165 pounds of crystallized sulphate of sea, (Glauber salts,) as long as a precipitate is formed. This precipitate is an almost pure sulphate of lime, while the acetate of soda remains in a clear solutions. Filtration separates this from the deposit. For the given quantities no more water sheuld be used than GOO pounds altogether. The solution is then placed in the boiler; 125 pounds of blue vitriol are aded, and the further treatment is the same as for a verdi-gris solution.
3. With vinegar.
The vinegar, or acetic acid, must be pure or distilled; but the required quantity depends entirely on its strength. The method of ascertaining this is given in another article. As an equivalent to the use of 100 pounds distilled verdigris, or 100 pounds of arsenic, 60 pounds of hydrated acetic acid is required. If this quantity is mixed with nine times its weight of water, so as to form 600 pounds of vinegar, (or, iu other words, if we have vinegar which contains 10 per cent of acetic acid,) it is only necessary to put the vinegar in the boiler and add 144 pounds of crystallized carbonate of soda, or add the soda until little or no more effervescence takes place. The solution is then acetate of soda, to which 125 pounds of blue vitriol is added, when the solution is acetate of copper, and may be further treated as such. If the same amount of acetic acid is contained in more vinegar, a larger quantity will be needed to be saturated by 144 pounds of carbonate of soda. It may be brought to about 600 pounds by evaporation. To avoid the latter necessity, however, the amount of the weak vinegar is previously determined which will contain 40 pounds of acetic acid. Suppose it is 900 pounds. Of this, 600 pounds is placed in the verdi-gris boiler, and the balance in the arsenic boiler. If necessary, water is added, to obtain the right quantity of liquid in the latter. It is then boiled, and, gradually, 144 pounds of crystallized carbonate of soda are added, until effervescence stops. In the vinegar contained in the verdigris boiler, 125 pounds of blue vitriol is in the mean time dissolved, and when both solutions are ready, that is, when nothing is left undissolved, they are poured together. The vinegar may also be placed in the arsenic boiler, and as soon as all the arsenic is dissolved in the soda solution, (which goes on more rapidly than without soda,) the blue vitriol may be thrown in, dissolved, and drawn off; or the green may be allowed to form in the boiler itself.
All these variations are permitted, and give different greens, as well in regard to size of grains as to shade. The method of using only two thirds as much acetic acid as is present in 100 parts of crystallized verdigris is, in most cases, mere economical than the method of changing all the vinegar first into acetate of lime, and using sulphate of soda in place of the car-bonate, in order to obtain acetate of soda. The shades of green obtained without the use of lime compounds are also clearer and purer, and no sulphate of lime or plaster has a chance to mix with the paint. The same method may also be followed with strong vinegar, taking only two thirds of the otherwise required 60 pounds of hydrated acetic acid in the mass of vinegar, putting the vinegar and the blue vitriol together, boiling the arsenic with the carbonate of soda, and then proceeding as described.