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nitrate and of the sulphate of iron, and in others acetic acid is present, as wellas the nitric and sulphuric. In specific gravity nitrates of iron range from40° to 120 0 Tw. Some of the varieties are prepared from copperas, some fromscrap iron, and others from both. Previously made nitric acid is used in somecases, whilst in others the iron is dissolved by nascent nitric acid, generatedby the aCtion of sulphuric acid upon nitrate of soda.

Taking first the k ‘ blue ” irons, used for dyeing Prussian blues upon silk orcotton, we find that they are “ sharper ” than the “ black” and “ common ”irons. They contain, in other words, a relatively larger amount of acid and asmaller of iron. If they are too “ dead ”—that is, if the proportion of ironbe too great—a large part of the colour formed will be deposited, not on thefibre, but at the bottom of the dye-beck, and the part which is fixed upon thegoods will be uneven, flat, and loose. Still the blue nitrate of iron must notbe too raw, or the shades resulting will be meagre, and the fibre will be indanger of being “ tendered ” by the free acid.

For dyeing cotton-yarns or unmixed cotton piece-goods, a blue iron madefrom copperas, and brought as closely as possible to a perfect per-salt, willgive shades superior to a pure nitrate made by the aCtion of aquafortis uponscrap iron. The following formula will give satisfaction :—Put into a largecask, capable of holding at least 130 gallons, 5 cwts. of dry, clean copperas.Pour upon it 130 lbs. of double aquafortis (nitric acid, at 64°Tw.),and stir thewhole well together, so that every part of the copperas may come in contactwith the acid. During this operation care must be taken to avoid the suffo-cating fumes which are given off in great quantities. On this account themanufacture of nitrate of iron is best carried on in open sheds where the windmay have free play, or under a hood, connected with a chimney having apowerful draught. At night the mixture is thoroughly stirred up again. Thestirring should not be too violent. The operator should avoid hasty circularmovements, and try, instead, to turn over every portion of the copperas,thrusting his pole to the very bottom, and working as if groping with the endfor some lost article. The stirring is repeated the second day, morning andnight, and on the morning of the third day ; the third night it will be finished.The copperas, if the operation has been successful, will be found entirely con-sumed, or perhaps a few pounds may remain at the bottom of the cask. It isthen let down with water to about 70° or 8o° Tw., well stirred up, allowed tosettle, and drawn off into carboys. If the ingredients are good, and theprocess has been carefully conducted, the resulting liquid will be clear andbright. It is, of course, a nitro-sulphate of the peroxide of iron. If any ofthe copperas has not dissolved in the nitric acid, but has been merely takenup by the water added for dilution, a small quantity of proto-salt of iron(sulphate) will be present. This iron, if preserved from light and fromextremes of temperature, keeps well. Still, especially in summer, it is notadvisable to make more than a fortnight’s consumption at once.

If mixed piece-goods with a cotton warp, such as coburgs, delaines, &c.,have to be dyed blue, and if the worsted has first been got up to the requiredshade with one of the aniline blues, a blue nitrate of iron made from copperasIs not admissible, since it works to some extent upon the worsted as well asupon the cotton, and injures the tone of the former. If a light or sky-blue isintended, or if the blue is to serve as the basis of a green, the lollowing