This acid, which abounds in wood sorrel, and which, combined with a small portion of potash, as it exists in that plant, has been sold under the name of 'salt of lemon, to be used as a substitute for the use of that fruit, particularly for discharging ink-spots and iron-moulds, was long supposed to be analogous to that of tartar. The oxalic acid is a good test for detecting lime, which it separates from all the other acids, unless they are present in excess. It has, likewise, a greater affinity for lime than for any of the other bases, and forms with it a pulverulent insoluble salt, not decomposable except by fire, and turning syrup of violets green. Some fatal accidents have occurred from persons mistaking this salt for Epsom salts; two or three drachms of the oxalic acid acting as a violent poison.