Next, M. Maumend examined the yellow mother liquor from the first crystal. This, in evaporation, yielded a crop of beautiful crystals, of which grms. gave on calcination only 0.010 of sulphate of lime, mixed with a little iron, and the residue exhibited no reaction on reddened litmus. By a crystallization from distilled water, this purification was almost complete, of well dried orystals giving only 0.002 of non-alkaline residue.
The way to obtain pure oxalic acid then, is to dissolve the ordinary acid in sufficient water to give 10 or 20 per cent. of crystals according to the impurity of the sample. The first crystals are rejected, and the mother liquor is evaporated to furnish a fresh crop, which after two or three crystallizations will be found to be quite free from alkaline oxalate. How found similar results, when following Mohr's method, in which the directions are to leave a large quantity of the acid undissolved by lukewarm water—the author evideutly being aware of the difficulties threatened —and relying upon the acid oxalates being left undissolved. How thinks that he may have dissolved these up by using water in too great quantity or of too high temperature, but despair ing of the whole proeess, he dissolved all the crops of crystals together in nearly boiling water, with the addition of enough nitric acid to make the liquid thoroughly acid. The crystals deposited in cooling were in thick prisms, and when washed and pressed they left a very small residue. After two crystallizations of these, a crop of crystals was obtained, which when dry left only •016 per cent. of a reddish coloured, slightly alkaline residuum, and the mother liquor of the crop preceding these gave, on evaporation, crystals approaching • 0159 per cent. of a similar residue, while from the mother liquor of both these crops evaporated together, crystals were obtained of such purity that the residue from about 30 grains could not be weighed. As M. Maumene's purest
crystals contained 0.09 per cent. of residuum, it is evidently an excellent plan to render the original water strongly acid when purifying oxalic acid.
Oxalic acid forms a large number of sults, of which the following only possess any commercial importance : The acid, or bin-oxalate of potash, originally procured, as already described, from the wood sorrel (oxalis acctosella). The manufacture from this source still holds its ground in some parts of Germany and Switzerland. It erystallizes in oblique rhombic prisms, and dissolves in 14 times its amount of boiling water.
The quadroxalate is made in a similar manner to the binoxalate, but three equivalents of oxalic acid are added to the neutral compound. It crystallizes in colourless transparent prisms, The neutral ammonia oxalate is prepared by neutralizing oxalic acid with carbonate of ammonia and crystallizing. It is used in the laboratory for the detection and determination of lime.
Oxalic acid is consumed chiefly by dyers and printers as a discharger in certain kinds of calico printing, as well as in woollen dyeing and printing, and in silk dyeing. Its cleansing properties are very great, and though it can scarcely be called a staple article of manufacture, it is undoubtedly of no small importance. For whitening leather and cleaning boot-tops it is invaluable, as well as in the bleaching of straw used in the making of bonnets, and for removing ink stains and iron moulds from linen. In cleaning copper utensils, and in many other ways, it may be used with great advantage over the more commonly employed mineral acids.
The largest manufacturers of acetic acid in this country produce about 20 tons weekly. The price has been reduced in a few years from 16d. to 5d. per lb.
A. L.