Page:The American Cyclopædia (1879) Volume XII.djvu/772

 T58 OXALIC ACID OXALIS effloresce slightly, and gently heated they be- come opaque, and lose two atoms (28*5 per cent.) of water, their composition then being H 2 C 2 O4. The crystals may crumble to powder, and even be almost wholly sublimed, without decomposition; but the other atom of water is expelled only at a decomposing heat, when the compound is converted into carbonic and formic acids and carbonic oxide. If the whole of the water be abstracted by treatment with strong sulphuric acid, the elements of dry oxalic acid are instantly resolved into equal volumes of carbonic acid and carbonic oxide. Two salts of oxalic acid are of especial importance, the binoxalate of potash and oxalate of lime. The former, known as salt of sorrel, sometimes im- properly called salt of lemons, is used to remove ink stains from linen, which it does by form- ing a soluble double salt of potassium and the metal whose oxide or compound produces the stain. For lime oxalic acid has a very strong affinity, separating it from its solution in much stronger acids, and converting it into an insolu- ble oxalate. The acid is consequently an excel- lent test of the presence of lime in solutions. Oxalic acid is a corrosive poison, extremely virulent and rapid in its effects when taken into the stomach in large doses ; and from the resemblance of its crystals to those of Epsom salts, it has often been sold and administered instead of this purgative with fatal effects. Emetics and the stomach pump may be im- mediately applied, but the true antidote is copious draughts of water containing pulver- ized chalk or magnesia. These neutralize the acid, forming with it an insoluble oxalate of lime or magnesia, either of which is harmless. The salts formed by oxalic acid with potassa or ammonia are also poisonous, and consequently these alkalies are not to be used as antidotes. Some of the plants mentioned above, which contain oxalate of potassa, are efficient anti- scorbutics, and the acid itself has been used for this purpose. Oxalic acid is largely em- ployed in calico printing for discharging col- ors ; it is also used for cleaning the straw of bonnet makers and the leather of boot tops, and for removing stains of ink and iron rust from fabrics. Many tons of oxalic acid are now made weekly in England for the calico printers, by heating saw dust with a mixture of hydrate of potash. A concentrated solution of mixed caustic soda and potash, of specific grav- ity 1'35, is prepared, containing two atoms of hydrate of soda to one of hydrate of potash. Saw dust is introduced in order to form a thick paste, and this is placed in layers on heated iron plates, and stirred constantly while the temperature is gradually raised. The heat is continued for three or four hours, taking care to avoid charring. The mass becomes thoroughly dry, and finally contains 28 to 30 per cent, of oxalic acid in combination with soda. Hydrate of lime converts the oxalate of soda into oxalate of lime, from which oxalic acid is obtained by treatment with sulphuric acid. OXALIS (Grr. bv$, sour, the foliage containing an acid, watery juice), a genus of plants of which the common wood sorrel is a familiar representative. This and a few other genera for- merly composed the family oxalidacece, which modern botanists have reduced to a tribe of the geranium family (geraniacece). The genus contains about 230 species, mostly herbs, or a few having somewhat woody stems ; many have bulb-like rootstocks; some have no stem above ground, and all have leaves of three or more leaflets. The flowers are regular, with five se- pals and as many petals ; stamens ten, often uni- ted at the base, with the alternate ones short- er ; ovary five-lobed, five-celled, with five dis- tinct styles; the membranaceous, oblong cap- Common Wood Sorrel (Oxalis aceto:ella). sule five-celled, each cell opening on the back and liberating two or more seeds ; flowers soli- tary or in many-flowered clusters. Some species produce inconspicuous and particularly fruit- ful flowers, which are fertilized in the bud. The genus is widely distributed, but the great- er number of species are natives of tropical America and southern Africa. Three species are found in the Atlantic states, one of which, the yellow wood sorrel (0. stricta), is very abun- dant, and makes its appearance in cultivated grounds as a weed ; it has running subterrane- an shoots, leafy branching stems, which are at first erect, and then spreading upon the ground, and small yellow flowers in clusters of five or six on axillary peduncles. Our other two spe- cies are stemless, their leaves and scapes arising from a rootstock or scaly bulb. The common wood sorrel, 0. acetosella, also a native of Europe and Asia, is common in woods from Pennsylvania northward to Canada, and it ex- tends to the Pacific. The long petioles bear three obovate, delicate green leaflets, and the flower stalks, 2 to 5 in. high, bear each a solitary flower, with white petals beautifully veined with red. The foliage is pleasantly sour, owing to the presence of binoxalate of potash. Before the discovery of the method