COPPERAS is the sulphate of iron, and is commonly called green vitriol. If sulphuric acid be diluted with water, and be poured upon iron, much effervescence will be seen : the metal will be dissolv ed, and the solution, when evaporated, will exhibit the sulphate of iron, or com mon copperas, which is a neutral salt in a very impure state. Copperas is the basis of many dyes: it gives a fine black, i though it rather subjects the material to decay, unless used with extreme caution, the least excess occasioning the cloth, &c. to rot very soon. It seems that wool is more affected by it than felt, as is ob vious from the greater duration of hats beyond what broad cloths, &c. exhibit when dyed black. Ink owes its rich blackness principally to the copperas it contains ; and our fine black leathers are equally indebted to its powerful quali ties, which so firmly fix the colour on all occasions. Many servants are in the habit of cleansing their copper kitchen utensils with green vitriol, which is ex tremely dangerous : the copperas is highly corrosive, and disengages a very large portion of the copper, which cannot be always removed, even when much pains are taken, the salt being buried under projecting rims, rivets, &c..
We are apt to believe that many most painful and dangerous complaints have resulted from this, though probably they may have been assigned to other suppos ed causes.
Mr. Murdoch, of Cornwall, obtained a patent for extracting copperas from mun die, and other ores containing sulphur, zinc, or arsenic. He washed the.calcined mundic, &c. and by evaporating the li quid produces chrystals of copperas. it is probably owing in a great degree to the quantity of green vitriol it contains, that ink is so efficacious in the cure of burns where' the skin is not off; but it should be applied without delay. Where copperas comes in contact with metals, it occasions an oxide to be formed, which is highly prejudicial to linens, &c. its well as to health. When it acts upon iron, it produces a stain called iron-mould, which may, however, be easily removed, if at tended to in doe time, by the use of ve getable acids ; especially the salt of le mons, and partially by cream of tartar, which is of ten sold by those itinerant knaves, who impose it on the ignorant throughout the country for the concen tratedealt of that fruit.