fine powder, and washing in large quantities of hot distilled water. Pure calomel in the form of a yellowish white insipid powder remains.

657. It was formerly the custom to submit calomel to very numerous sublimations, under the idea of rendering it mild; but these often tend to the production of corrosive sublimate; and the calomel of the first sublimation, especially if a little excess of mercury be found in it, is often more pure than that afforded by subsequent operations.

658. Here follows the method directed in the Pharmocopœia, for the production of calomel, which for the reasons given above we also omit. 659. It will be observed, continues Mr. B., that in these processes the operation consists in reducing the perchloride to the state of protochloride, by the addition of mercury. Various modes have, however, been adopted for the direct formation of calomel; two of these may here be noticed, of which the first is in the humid way, as devised by Scheele and Chenevix. It is as follows:

660. Form a nitrate of mercury, by dissolving as much mercury as possible in hot nitric acid; then dissolve in boiling water a quantity of common salt, equal to half the weight of the mercury used, and render the solution sensibly sour by muriatic acid, and pour the hot nitrate of mercury into it. Wash and dry the precipitate.

661. If this process be carefully performed, and the precipitate thoroughly edulcorated, the calomel is sufficiently pure.

662. The second process, however, or that by which calomel is directly formed in the dry way, appears on the whole the least exceptionable for the production of this very important article of pharmacy. It is the method followed at Apothecaries' Hall, sanction having been obtained for its adoption from the Royal College of Physicians. Fifty pounds of mercury are boiled with seventy pounds of sulphuric acid to dryness, in a cast-iron vessel: sixty-two pounds of the dry salt are triturated with forty pounds and a half of mercury, until the globules disappear, and thirty-four pounds of common salt are then added. This mixture is submitted to heat in earthen vessels, and from ninety-five to 100 lbs. of calomel are the result. It is to be washed in large quantities of distilled water, after having been ground to fine and impalpable powder.

663. Protochloride of mercury is usually seen in the form of a white mass of a crystalline texture; and, when very slowly sublimed, it often presents regular four-sided prisms, perfectly transparent and colorless. Its specific gravity is 7.2. It is tasteless, and very nearly insoluble in water. It can scarcely be called poisonous, since in considerable doses it only proves purgative. By exposure to light it becomes brown upon its surface. If scratched it gives a yellow streak which is very characteristic, and does not belong to the perchloride. When very finely levigated it becomes of a buff color.

664. It consists of one proportional of mercury, 190+ one proportional of chlorine 33.5, and its representative number is 223-5.

665. Native chloride of mercury, or mercurial horn ore, has been found in Germany, France,

and Spain, usually crystallised, and sometimes incrusting and massive. Brande.

666. Iodine and mercury unite in two proportions, forming the protiodide, which is a yellow compound, and the priodide or the deutiodide which is red. They are insoluble in

water.

667. Salts of mercury.-Protosulphate of mercury is formed by boiling mercury in equal or double its weight of sulphuric acid. This salt requires 500 parts of water for its solution. If heated for some time to a pretty high temperature, part of its acid is expelled, and a hard gray mass is formed. When this is removed from the fire, and hot water is poured upon it, a yellowish-colored substance is formed, which was formerly called turpeth or turbith mineral, it is a super-sulphate of mercury, and a bipersulphate remains in solution.

668. Chlorate of mercury.—Both the oxides of mercury dissolve in chloric acid. Both the salts, when heated, give out oxygen, and are converted into per-oxide and per-chloride of mercury. An. de Chim. 95, 103.

669. Cyanide of mercury.—This may be formed by boiling one part of finely powdered red oxide of mercury, with two of Prussian blue, in eight parts of water. In this way a solution is obtained, which, if filtered while hot, deposits yellowish white crystals which are the cyanide.

670. Nitrates of mercury.-These are the proto-nitrate and per-nitrate. The first is formed by dissolving mercury in nitric acid, without the assistance of heat; this solution yields by evaporation the salt in question. The second is procured by using heat in the solution, and the metal thereby becomes more highly oxidated.

671. The substance commonly called red precipitate, is produced by exposing the nitrates to a heat gradually raised to upwards of 600°, nitric acid is given off, and a brilliant red substance remains, which is properly a nitro-oxide of mercury, and is thus designated in the Pharmacopoeia.

672. Fulminating mercury.-The account of this preparation we extract verbatim from Dr. Henry's elements. Mercury is the base of a fulminating compound, discovered by the late Mr. E. Howard. To prepare this powder 100 grains (or a greater proportional quantity, not exceeding 500), are to be dissolved with heat in a measured ounce and half of nitric acid. The solution being poured cold upon two measured ounces of alcohol, previously introduced into any convenient glass vessel, a moderate heat is to be applied till effervescence is excited. A white fume then begins to undulate on the surface of the liquor, and the powder will be gradually precipitated on the cessation of action and re-action. The precipitate is to be immediately collected on a filter, well washed with distilled water, and cautiously dried in a heat not exceeding that of a water bath. The immediate washing of the powder is material, because it is liable to the re-action of the nitric-acid; and, while any of that acid adheres to it, it is very subject to be decomposed by the action of light. From 100 grains of mercury about 120 or 130 of the powder are obtained (see Phi

losophical Transactions, 1800). This powder has the property of detonating loudly in a gentle heat, or by slight friction. Hence it has been proposed as a means of firing ordnance. But an accident described by professor Silliman, as having happened in his laboratory, shows that this fulminating compound explodes from such trifling causes as not to be kept without danger, even when secured from friction or heat. It has been shown from the experiments of Liebeg and Gay Lussac (Au. de Ch. et de Phys. 24 and 25), that fulminating mercury owes its properties to a peculiar acid united with oxide of mercury, which may be transferred from it to alkaline and other bases, but is not obtainable in a separate state. To this acid they have given the name of

fulminic.

673. Sulphurets of mercury are two, the one formerly called Æthiop's mineral, and the other cinnabar. The first is obtained by triturating for a length of time one part of mercury with three of sulphur, or by pouring at once mercury into melted sulphur. If the black sulphuret or Æthiops be fused together and sublimed, the red, or vermillion sulphuret is procured, which is the cinnabar of former times. Native cinnabar furnishes most of the mercury which is employed in commerce, this compound being distilled with iron filings. Æthiop's mineral is a proto-sulphuret or sulphuret; cinnabar is a bisulphuret of mercury.

674. With most of the metals mercury combines, and forms a class of compounds called amalgams; in the case of these combinations mercury loses its fluidity. It is a curious fact, that a solid amalgam of lead, mixed with one of bismuth, instantly becomes fluid.

675. Combination with mercury gives to some metals a facility of uniting with oxygen. See the word AMALGAM.

COPPER.

676. Copper is found native, and in various states of combination; the copper of commerce, too, is occasionally contaminated with other metals, as antimony, lead, and arsenic; and Berzelius states, that a small quantity of charcoal and sulphur are always found in it. Philosophical Mag. xlvii. 206. To be rendered perfectly pure it must be dissolved in muriatic acid, and into the solution a polished plate of iron is to be immersed, upon which the pure copper is precipitated. When the metal has thus been purified, it is to be washed with dilute sulphuric, or muriatic acid, and it may be fused, or kept in a divided form.

677. Copper has great malleability, ductility, and tenacity. It fuses at a dull white heat, and, if the heat be urged on, it evaporates in visible fumes.

678. The native copper is met with in different forms, massive, granular, and in crystals. It is found in Cornwall, Saxony, Siberia, Sweden, &c. It is also met with in America.

679. Oxides of copper.-This metal is susceptible of two degrees of oxidisement; the one combination constituting the protoxide, the other the peroxide of the metal. The first, or lowest stage of oxidisement, forms a red substance; and the second, or maximum, is black.

680. The protoxide occurs native. It may be produced artificially, by mixing metallic copper and peroxide of copper in muriatic acid. If potassa be added to this solution, a hydrated protoxide is obtained, which falls to the bottom, which is of an orange color; if quickly dried, without being subjected to oxygen, it becomes red.

681. The black, or peroxide, is procured by precipitating nitrate of copper with carbonate of potass. A simple ignition of the nitrate will produce it.

682. Chlorine with copper.-Copper is acted on forcibly by gaseous chlorine, and, when these materials are treated together, two compounds are simultaneously produced, the proto-chloride and per-chloride of copper. The first of these compounds was called resin of copper by Boyle. It is insoluble in water, but soluble in muriatic acid; the color of it is dark brown, but it acquires a green hue by exposure to the air. This substance remains in the retort after the distillation of a mixture of two parts of corrosive sublimate (bi-chloride of mercury) and one of copper filings.

683. The per-chloride may be produced by dissolving peroxide of copper in muriatic acid, and evaporating to dryness at a heat below 400°. This compound is of a yellow color, but dissolved in water it becomes eventually green.

684. An iodide of copper may be precipitated from solutions of the metal, by hydriodic acid. This substance is brown and insoluble.

685. Salts of copper.-Muriatic acid does not act readily on metallic copper; but it freely dissolves the peroxide, and thus forms the permuriate. A proto-muriate is also obtained by digesting copper filings with the peroxide of the metal in muriatic acid. A native submuriate of copper is found in Chili and Peru; and it is a submuriate of copper that is formed by the destructive action of sea-water upon the copper sheathing of ships, the oxygen necessary to the formation of the muriate being derived from the air of the atmosphere. Now, according to the views of Sir H. Davy, copper can only act upon sea-water when in a positive state, and that philosopher was therefore led to conceive, that if the electric state of the copper were reversed, by bringing it into contact with some metal of more energetic electrical power, the action of the seawater would cease. Philosophical Transactions, 1824. This led him to a discovery which promises to be most important in its practical consequences, viz. that extensive surfaces of copper may be completely protected from the corroding effects of sea-water, by placing comparatively small quantities of malleable or cast iron, in contact with the copper sheathing of a ship; and it has been found that the covering of vessels so protected is uninjured, even by long voyages, in tropical countries. This discovery has been applied by Dr. Bostock to the protection of utensils employed for culinary purposes.' An. of Philos. viii. p. 76. Henry.

686. Chlorate of copper is formed by dissolving peroxide of copper in chloric acid. This salt is of a bluish-green color, not easily crytallised, and is deliquescent,

687. Iodate of copper is procured by precipitation from solutions of copper, by means of the iodate of potassa or other alkaline iodates.

688. Nitrate of copper is obtained by direct solution of the metal in dilute nitric acid; and a sub-nitrate is obtainable by adding a small portion of alkali to the solution of the nitrate. There appears to be no proto-nitrate of copper, for protoxide of copper, digested in very dilute nitric acid, is resolved into peroxide, which dissolves, and into metallic copper. Potassa forms in solution a bulky blue precipitate of hydrated peroxide of copper, which, when boiled in potassa or soda, becomes black from the loss of its combined water. Brande.

689. If peroxide of copper be dissolved in ammonia, a bright blue liquid will be produced, from which blue crystals may be procured by evaporation, and these constitute the ammoniaret of copper, or cuprate of ammonia.

690. Sulphates of copper.-The blue salt which is formed by digesting strong sulphuric acid with copper is a sulphate; but it is better to use the oxide of the metal for the preparation, otherwise, part of the sulphuric acid being decomposed, and furnishing oxygen to the metal, it is dissolved. The sulphate, or persulphate of copper, is a regularly crystallised salt, which has been called blue vitriol, or Roman vitriol. Upon a large scale this salt is formed by exposing to the air and moisture a sulphuret of copper. This preparation is the salt of Venus of the alchemists.

691. A sub-sulphate of copper may be formed by adding potassa or ammonia carefully to a solution of the sulphate; and Dr. Thomson has recently described a quadri-sulphate, consisting of 1 atom of base + 4 atoms of acid.

692. Sulphite of copper may be obtained by passing sulphurous acid gas into a vessel containing water and oxide of copper. See An. de Chim. 83.

693. Phosphoric acid unites with the oxide of copper in two proportions, viz. into a bi-phosphate and phosphate. The latter has been found in a native state near Cologne.

694. Carbonate of copper is formed by exposing the metal to a damp air; and it may be produced by adding alkalis, in their carbonated state, to solutions of copper. There is a fine blue preparation of copper, which is called verditer, and principally used by silver-refiners; this is formed by adding carbonate of lime to the nitrate of copper.

695. Native carbonate of copper is met with of a green and of a blue color; the first (malachite) is found in Siberia, it has been met with in Cornwall. The blue carbonate is found in Bohemia, and near Lyons, &c. One variety of this is sometimes called the mountain blue.

696. Verdigris is an acetate of copper; by the solution of this substance in distilled vinegar, a binacetate is formed. A sub-acetate is procurable by acting on verdigris with water. Berzelius speaks of other proportionals of acetic acid with oxide of copper, An. of Phil. N. S. 8. 188.

697. A ferro-cyanate of copper is obtained by adding ferro-cyanate of potassa to a dilute solution of sulphate or nitrate of copper, or to the

muriate of the metal. This substance has been recommended by Mr. Hatchett to be used as a brown piginent.

698. Sulphuret of copper exists native in two forms; the one is black and is capable of being artificially formed by melting in a glass tube three parts of iron filings with one part of sulphur. The other is a bi-sulphuret, which forms the ore of copper called pyrites.

699. Phosphorus and copper unite by fusion, and form a phosphuret which is of a grayishwhite color.

700. On the alloys of copper, as some of them are important, we shall extract some paragraphs from Mr. Brande's Manual. With gold it forms a fine yellow ductile compound, used for coin and ornamental work. Sterling or standard gold consists of 11 gold + 1 copper. The specific gravity of this alloy is 17-157. With silver it forms a white compound, used for plate and coin. Lead and copper require a high red heat for union; the alloy is gray and brittle.

701. Brass is an alloy of copper and zinc. The metals are usually united by mixing granulated copper with calamine and charcoal; the mixture is exposed to heat sufficient to reduce the calamine and melt the alloy, which is then cast into plates. The relative proportion of the two metals varies in the different kinds of brass; there is usually from twelve to eighteen per cent. of zinc. Brass is very malleable and ductile when cold; and its color, and little liability to rust, recommend it in preference to copper for many purposes of the arts. According to M. Sage a very beautiful brass may be made by mixing fifty grains of oxide of copper, 100 of calamine, 400 of black flux, and thirty of charcoal powder; melt these in a crucible till the blue flame is no longer seen round the cover, and, when cold, a button of brass is found at the bottom, of a golden color and weighing one-sixth more than the pure copper, obtained from the above quantity of oxide.

702. The analysis of brass may be performed by solution in nitric acid; add considerable excess of solution of potass and boil, which will dissolve the oxide of zinc and leave that of copper, wash the latter, and dry, and heat to redness; 125 parts indicate 100 of copper. The zinc in the filtered alkaline solution may be precipitated by carbonate of soda, having previously added a small excess of muriatic acid; wash this precipitate, dry it, and expose it to a red heat; it is then oxide of zinc, 123 parts of which, indicate 100 of the metal.

703. Tutaneg is said to be an alloy of copper, zinc, and a little iron; and tombac, Dutch gold, similor, Prince Rupert's metal, and pinchback are alloys, containing more copper than exists in brass, and consequently made by fusing various proportions of copper with brass. According to Wiegleb, manheim gold consists of three parts of copper, and one of zinc. A little tin is sometimes added, which, though it may improve the color, impairs the malleability of the alloy.

704. Speculum metal is an alloy of copper and tin, with a little arsenic; about 6 copper, 2 tin, 1 arsenic. On this subject the reader is referred to Mr. Edwards' experiments (Nicholson's Journal 4to. iii.) Bell-metal and bronze are alloys of

copper and tin; they are harder, and more fusible, but less malleable than copper; the former consist of three parts of copper and one of tin; the latter from eight to twelve of tin with 100 of copper. A little zinc is added to small shrill bells.

705. Vessels of copper used for culinary purposes are usually coated with tin, to prevent the food from being contaminated with copper. Their interior surface is first cleaned, then rubbed over with sal-ammoniac. The vessel is then heated, a little pitch spread over the surface, and a bit of tin rubbed over it, which instantly unites with and covers the copper. Brande.

706. Respecting the alloys of copper much valuable information may be found in the 4th volume of Bishop Watson's Chemical Essays, and in Aikin's Dictionary of Chemistry, article BRASS &c. From a recent investigation of them Mr. Dalton finds that in all alloys of copper which are characterised by useful properties, the ingredients enter in atomic proportions; and it is probable that by attention to these proportions, the manufacture of the artificial alloys may be greatly improved.

707. Most of the copper of commerce is obtained from copper pyrites, or yellow copper ore, which is a compound of sulphur, iron, and copper, in such proportions, as render it probable that it is composed of two atoms of proto-sulphuret of iron, and one atom of per-sulphuret of copper, with a little arsenic and earthy matter (An, of Philos. N. S. lxxxiii. p. 301). The sulphur and arsenic are separated by roasting, and the copper is obtained by repeated fusions, in one of which an addition of charcoal is made. Henry.

IRON.

708. Iron, although not so malleable as gold and silver, is still more ductile than either of them. This metal exists in such abundance that few fossils are entirely free from it. Iron is of a bluish-white color, and is susceptible of very high polish. It is considered by many as of meteoric origin, and indeed, masses of native iron have been seen to fall from the atmosphere. It is one of the most infusible of the metals.

709. Iron and oxygen.-The rusting of iron from exposure to a moist atmosphere, is, in fact, the combination of it with oxygen. It combines with this principle in at least two proportions, forming protoxide and peroxide. The protoxide may be artificially made by precipitating a solution of sulphate of iron with potassa, washing and evaporating it. It is black; Gay Lussac has supposed that in drying, an additional proportion of oxygen is absorbed, and thus that a deutoxide of the metal is formed. Mr. Brande says there is some reason to doubt the accuracy of this conclusion.

710. Protoxide of iron may be obtained by burning iron in oxygen gas; this process forms a beautiful experiment, it was first described by Dr. Ingenhous.

711. When this protoxide is boiled in nitric acid, and precipitated by ammonia, then washed dried and calcined, it is converted into a reddish or brown oxide. This is the peroxide of the

metal.

712. Corresponding with these two oxides of iron, there appear to be two hydrates, or hydrooxides, obtainable by precipitating the acid solutions by a fixed alkali. It is, however, difficult to obtain a pure hydrate of iron, on account of the facility with which it parts with water.

713. The native oxides of iron, says Mr Brande, constitute a very extensive and important class of metallic ores. They vary in color, depending upon mere texture in some cases; in others upon the degree of oxidisement. Some varieties are magnetic, and those which contain the least oxygen are attracted by the magnet.

714. Magnetic iron ore is generally black, with a slight metallic lustre. It occurs massive and octahedral. It is often sufficiently magnetic to take up a needle. It occurs chiefly in primitive countries, and is very abundant at Roslagen in Sweden, where it is manufactured into a bar-iron particularly esteemed for making steel.

715. Another variety of oxide of iron is called iron glance, and micaceous iron ore. It is found crystallised, of singular beauty, in the isle of Elba, and occasionally among the volcanic products of Vesuvius, and the Lipari islands.

716. A third variety is hæmatite or red iron stone; it occurs in globular and stalactitic masses, having a fibrous and diverging structure. In this country it abounds near Ulverstone in Lancashire; and most of our iron plate and wire is made from it. Sometimes it is of a brown, black, or ochraceous color.

717. A fourth variety of oxide of iron is known under the name of clay iron stone, on account of the quantity of argillaceous earth with which it is contaminated. It is found in masses of different shapes and sizes, and sometimes in small round nodules like peas. Some of the globular masses are called ætites. is abundant in the coal formations of Shropshire, South Wales, Staffordshire, and Scotland.

It

718. Though this is far from being the purest iron ore found in this country, it is the chief source of the cast and bar iron in ordinary use. Its employment is chiefly referrible to the coal which accompanies it.

719. The essential part of the process by which these ores of iron are reduced, consists in decomposing them by the action of charcoal at high temperatures. The argillaceous iron of Wales, Shropshire, &c. is first roasted and then smelted with lime-stone and coke; the use of the former being to produce a fusible compound with the clay of the ore, by which the latter is enabled to act upon the oxide, and to reduce it to the metallic state. Brande.

720. Chlorine and iron unite in two proportions, forming the proto-chloride, and the perchloride; these products have not been much examined.

721. Iodine also unites with iron into a brown fusible compound, which is an iodide of the metal, and which, when acted upon by water, becomes a hydriodate of a green color.

722. Sulphur and iron.-There is a proto-sulphuret and a bi-sulphuret of iron, the latter of which is exclusively a natural product, and is found abundantly; it is called iron-pyrites. The former may be prepared by melting iron filings

and sulphur together; this is also found native, but it is distinguishable from the bi-sulphuret by its black color and by its being magnetic, it is called indeed magnetic pyrites, to distinguish it from the common pyrite or yellow sulphuret. The magnetic pyrite is found to contain just half the sulphur which exists in the other.

723. Carbon and iron.-With carbon, iron unites in various proportions, and a great difference is found in the properties of these compounds, according to the proportion of their ingredients. On these varieties, indeed, together with an occasional union of a small quantity of oxygen, depend the different kinds and qualities of the metal found in commerce, and employed in the

arts.

724. There can scarcely, says Dr. Henry, be a more striking example of essential differences in external and physical characters being produced by slight differences in chemical composition, than in the carburets of iron, for steel owes its properties to not more than from to Tth its weight of carbon. This appears to be the only addition necessary to convert iron into steel; for, though it is proved that the best steel is made from iron which has been procured from ores containing manganese, yet careful and skilful analysis discovers no manganese in steel. An. de Chim. et de Phys. 3.

725. Steel is a compound, then, of iron and carbon, the proportions being variable; and the latter metal is converted into the former by a process which is called cementing, and which consists of heating bar-iron in contact with charcoal. We should say that what is called cast or crude iron contains oxygen and the base of silica, besides incidental admixtures; of this there are two species, the one containing more, the other less of carbon. By the process of puddling, as it is called (for an account of which see the eighty-first volume of the Philosophical Transactions), cast iron becomes converted into malleable, in other words it is made purer; and it is now called bar-iron, which is used, as we have just stated, for the formation of steel. By combining a still larger quantity of carbon with the bar iron, the fine cast-steel is procured; so that steel, though, like cast-iron, it is combined with carbon, most essentially differs from iron, by being without oxygen, silex, and other matters. 726. Plumbago is another carburet of iron; this is used for black lead pencils, and for covering iron in order to prevent rust. Iron unites with various metals in alloy.

727. Salts of iron.-Copperas, or green vitriol as it has been called, is a sulphate of iron. It is usually formed by dissolving iron filings in dilute sulphuric acid. When in solution this salt absorbs nitric oxide gas, and acquires a brown color: it also unites with chlorine, muriatic acid becomes formed, and in this case the water of solution becomes decomposed.

728. By exposure to air, or if treated with nitric acid, it is converted from a proto-sulphate into a per-sulphate. Sulphuric acid used to be formed from this salt by expelling it with heat; and when thus treated a peroxide of iron remained in the vessel. This residue was known

under the appellation of colcothar or caput mor tuum vitrioli.

729. This salt (the green vitriol) occurs native in several of the coal mines of this country; it is usually combined with pyrites.

730. Muriate of iron is formed by dissolving iron filings in muriatic acid. The proto-muriate is in crystals of a green color, the per-muriate is of a reddish brown. It is this last which is used in the preparation of the Pharmacopœia called tinctura ferri muriatis.

731. Nitrate of iron-The nitric acid acting upon iron produces also the green or proto-nitrate, in which the oxide is at the minimum of oxidation, and the red or per-nitrate, in which it is at the maximum.

732. Carbonic acid unites with the protoxide of iron, and forms a proto-carbonate

733. Ferro-cyanate of iron or Prussian blue.— We shall give an account of this substance in a distinct article. Here we shall confine ourselves to extracting the following remarks from Dr. Henry, respecting its nature and properties :—

734. Respecting the nature of Prussian blue a variety of opinions have been entertained, and it is still a subject on which chemists are by no means agreed. No theory respecting it can be entitled to notice that was anterior to Gay Lussac's discovery of cyanogen. His researches led him to believe that Prussian blue is a compound of cyanogen with metallic iron, and it is therefore not a prussiate but a cyanide; but Vauquelin, having directed his attention to this part of the subject, was still induced to regard it as a true prussiate. According to Mr. Porrett's view, it is a compound of ferro-cyanic acid with peroxide of iron. Berzelius, not admitting the existence of any such acid as the ferro-cyanic, regards Prussian blue as a compound of hydrocyanate of protoxide of iron with peroxide of iron, in proportions admitting of some variations (An. of Phil. N. S. 1. 444). Robiquet, on the other hand, considers it as a cyanide of iron combined with a ferro-cyanate of the peroxide and with water (An. de Chim. et Phys. 12 and 17). The subject, in its present state, appears to me very obscure, and I refer the reader, who is disposed to examine it, to the papers of Berzelius and Robiquet already quoted.'

For an account of the combination of iron with the gallic acid and tan, see the article INK in this Encyclopædia.

735. Acetate of iron. This combination may also, like the other salts of the metal, exist in two different states; it is a per-acetate of iron, which is much used in dyeing and calico-printing, see DYEING.

736. Proto-phosphate of iron may be formed by adding solution of phosphate of soda to the proto-sulphate of iron; and the per-phosphate by adding the same solution to the per-sulphate of

iron.

737. The proto-phosphate is found native, both in the form of a blue powder and in prismatic crystals. It has been improperly named native Prussian blue.

738. Iron unites with many other metals in the way of alloy.