Another.-Write on a sheet of paper any sentence with a transparent infusion of nut-galls, and dip the paper in a transparent solution of the sulphate of iron. The writing, which was before invisible, will now, on a slight exposure to the air, turns quite black. A neater way of performing this experiment will be by smearing the written parts over with a feather dipped in the solution of the metallic salt; it may also be reversed, by writing with the salt and smearing with the infusion. Another. If a letter be written with a solution of sulphate of iron, the inscription will be invisible, but if it afterwards be rubbed over by a feather dipped in a solution of prussiate of potassa, it will appear of a beautiful blue color.

Another.-Write a letter with a solution of nitrate of bismuth. The letters will be invisible. If a feather be now dipped in a solution of the prussiate of potass, and rubbed over the paper, the writing will appear of a beautiful yellow color, occasioned by a formation of prussiate of bismuth. lead or tartar emetic; moisten the writing (or drawing) and expose to a current of sulphuretted hydrogen gas. The lead will turn black, and the antimony orange brown.

Another.-Write with a solution of sugar of

Chemical Landscapes. These are drawn partly in Indian-ink and partly in sympathetic inks, which are only visible when gently heated. The picture represents ordinarily a winter scene, but when heated the sky becomes blue, the leaves green, and flowers and fruit are seen. The materials are as follows: Green, chloride of nickel; blue, pure chloride or acetate of cobalt; yellow, chloride of copper; brown, bromide of copper. If the picture is too highly heated it will not again fade.

Triturate in a mortar equal parts of silver foil and sulphate of potassa, until reduced to a fine powder; then wash out the salt, and mix the residue with a mucilage of equal parts of gum Arabic and water.

Brown Ink.

Digest powdered catechu, 4 parts, with water, 60 parts, for some hours; filter, and add sufficient of a solution of bichromate of potassa, 1 part in 16 of water.

Yellow Ink.

Blue Ink.

part.

bonate of potash, 16 parts, in 144 of water, for 24 2. Digest powdered cochineal, 8 parts, and carand add 24 of cream of tartar, with 3 parts of hours; then boil up with powdered alum, 4 parts, tartaric acid, and, when effervescence has ceased, another part of the acid, or enough to produce the color; let cool, filter, and boil the residue on the filter with 12 parts of water; filter again, mix the liquids and dissolve in them 24 parts of gum Arabic, and lastly part of oil of cloves. No iron ves els must be used in this process.

acid, 2 parts; dilute acetic acid, 80 parts; distil3. Digest powdered cochineal, 16 parts; oxalic led water, 40 parts, for 36 hours; then add powdered alum, 1 part; gum Arabic, 1 to 10; shake up, let stand for 12 hours, and strain.

4. Dissolve 1 part of carmine in 8 to 10 parts of aqua ammonia, and add mucilage of gum Arabic sufficient to reduce it properly.

ASSAYING OF METALLIC ORES.

Before metallic ores are worked upon in the large way, it will be necessary to inquire what sort of metal, and what portion of it, is to be found in a determinate quantity of the ore; to discover whether it will be worth while to extract it largely, and in what manner the process is to be conducted,

so as to answer that purpose. The knowledge requisite for this is called the art of assaying.

Assay of Ores in the Dry Way.

The assaying of ores may be performed either in the dry or moist way; the first is the most ancient, and, in many respects the most advanta

When cold it is ready for testing with the following solution.

Dissolve 50 grs. of crystallized permanganate of potassa in 20 oz. of distilled water, and keep it in a tightly corked bottle, marked "Standard Solution Permanganate of Potassa." To ascertain the standard of this solution, dissolve 10 grs. of iron piano wire in dilute hydrochloric acid in a narrow-mouth flask with gentle heat. Dilute to 10 oz. Take 1 oz. of the diluted iron solution and dilute to 20 oz. with distilled water in a white porcelain dish.

Allow the solution of permanganate to run slowly in from a graduated pipette, stirring constantly until the solution assumes a faint pink color. Record the amount used, this represents 1 gr. of metallic iron.

Proceed in the same manner to test the solution of ore first obtained, noting the amount required to produce the first tint of pink color. Divide this amount by the amounts required for 1 gr. of iron, and the result is the number of grains of metallic iron contained in the ore.

Tin Ores.

Mix a quintal of tin ore, previously washed, pulverized, and roasted till no arsenical vapor arises, with half a quintal of calcined borax, and the same quantity of pulverized pitch; these are to be put in a crucible lined with charcoal, which is placed in an air-furnace. After the pitch is burnt, give a violent heat for a quarter of an hour, and on withdrawing the crucible, the regulus will be found at the bottom. If the ore be not well washed from earthy matters, a larger quantity of borax will be requisite, with some powdered glass; and if the ore contain iron, some alkaline salt may be added.

In the Humid Way.

Dissolve the ore in hot muriatic acid, pass through the solution a current of sulphuretted hydrogen in large excess. Allow the precipitate to subside, add to it, with the aid of heat, nitric acid until no sulphuretted hydrogen is given off. This transforms the tin into stannic acid, wash carefully, dry, and weigh. Stannic acid contains 78.61 per cent. of tin.

Lead Ores.

As most of the lead ores contain either sulphur or arsenic, they require to be well roasted. Take a quintal of roasted ore, with the same quantity of calcined borax, a quintal of fine powdered glass, of a quintal of pitch, and as much clean iron filings. Line the crucible with wetted charcoal-dust, and put the mixture into the crucible, and place it before the bellows of a forge-fire. When it is red hot, raise the fire for 15 or 20 minutes, then withdraw the crucible, and break it when cold.

the zine will be found adhering to the neck of the retort in its metallic form.

In the Humid Way (Percy).

Take 20 grs. of the ore (finely pulverized) to be assayed. Digest it for 1 hour in nitric acid 1 part, water 2 parts, with a few drops of hydrochloric acid; add carbonate of ammonia dissolved in liquid ammonia until the reaction is strongly alkaline. Digest for half an hour, dilute with an equal bulk of distilled water; filter and mark the filtrate Sol. A.

Make a standard solution of zine by dissolving grs. of pure zinc in nitric acid and diluting to 10 oz. Sol. B.

10

Make a solution of sulphide of sodium, 1 oz. of saturated solution to 10 oz. of distilled water. Sol. C.

Take of solution chloride of iron, oz.; distilled water, 5 oz.; add aqua ammonia; separate all of the iron. Shake. Sol. D.

Take of solution B, 1 oz.; dilute to 3 oz.; add of solution D, 1 oz.; take in a graduated pipette of solution C, and add gradually to the mixture of B and D (stirring rapidly all the while), until the flocculent iron begins to change color to grayish black. Make a memorandum of the number of graduations of solution C required. This is the amount of sulphide of sodium necessary to precipitate 1 gr. of metallic zinc.

Take of solution A (diluted to 12 oz.) equal 6 oz.; add of solution D, 2 oz.; then with graduated pipette run in slowly the solution C until the flocculent iron begins to change color as before. The number of graduations required, divided by the number used in the former experiment, indicate the number of grains of metallic zine in 10 grs. of the ore, and represent the per centage likewise.

Copper Ores.

Take an exact troy ounce of the ore, previously pulverized, and calcine it well; stir it all the time with an iron rod without removing it from the crucible; after the calcination add an equal quantity of borax, the quantity of fusible glass, the quantity of pitch, and a little charcoal-dust; rub the inner surface of the crucible with a paste composed of charcoal-dust, a little fine powdered Cover the mass with common clay, and water. salt, and put a lid upon the crucible, which is to be placed in a furnace; the fire is to be raised gradually till it burns briskly, and the crucible continued in it for hour, stirring the metal frequently with an iron rod; and when the scoria which adheres to the rod appears clear, then the crucible must be taken out and suffered to cool; after which it must be broken and the regulus separated and weighed. This is called black copper; to refine which equal parts of common salt and nitre are to be well mixed together. The black copper is brought into fusion, and a teaspoonful of the flux is thrown upon it, which is repeated 3 or 4 times, when the metal is poured into an ingot mould and the button is found to be

fine copper.

In the Humid Way.

Make a solution of vitreous copper ore in 5 times its weight of concentrated sulphuric acid, and boil it to dryness; add as much water as will dissolve the vitriol thus formed. To this solution add a clean bar of iron, which will precipitate the whole of the copper in its metallic form. If the solution be contaminated with iron, the copper must be re-dissolved in the same manner and

precipitated again. The sulphur may be separated by filtration.

Volumetric Assay of Copper Ores. (Percy.) Dissolve 10 grs. of the copper ore finely pulverized and moistened with strong sulphuric acid, in strong nitric acid, adding the acid gradually; and when the fumes of hyponitric acid cease to be evolved, add a small amount of water and boil for a few minutes. Dilute to 10 oz. and treat with ammonia in excess, and it will become of a deep blue color. Set aside to cool, and prepare the following solution: Dissolve 500 grs. of granulated cyanide of potassium in 20 oz. of distilled water, and keep in a tight-stoppered bottle in the dark. Mark "Standard Solution Cyanide of Potassium." To ascertain the standard of this solution, dissolve 10 grs. of electrotype copper in dilute nitric acid and boil to expel hyponitric acid fumes, and dilute to 10 oz. with distilled water. Take of this solution 1 oz. and dilute to 5 oz. with distilled water, and allow the standard cyanide solution to flow very slowly into it at intervals, from a graduated pipette, and note the amount used to render it nearly colorless. This process takes from to of an hour. Proceed in the

same manner to test the solution of ore first obtained, noting the amount required to reduce the color to a faint lilac. Divide this amount by the amount found required for 1 gr. of metallic copper, and the result is the number of grains of metallic copper in the ore tested.

Take a common crucible, bore a number of small holes in the bottom, and place it in another crucible a size smaller, luting them well together; then put the proper quantity of ore in small lumps into the upper crucible, and lute thereon a cover; place these vessels on a hearth and surround them with stones about 6 in. distant from them; the intermediate space must be filled with ashes, so that the undermost crucible may be covered with

them; but upon the upper charcoal must be laid,

and the whole made red hot by the assistance of hand bellows. The antimony being of easy fusion is separated, and runs through the holes of the apper vessel into the inferior one, where it is col

lected.

with charcoal- dust, covering the crucible with another inverted and luted on, and exposing it to the strongest heat of a forge for an hour or more. The ore is very difficult to reduce. Arsenical Ores.

sels. Beat the ore into small pieces and put them This assay is made by sublimation in close ves into a matrass, which place in a sand-pot with a proper degree of heat. The arsenic sublimes in the vessel; when it must be carefully collected, this operation and adheres to the upper part of with a view to ascertain its weight. A single sublimation will not be sufficient. It is better to perform the first sublimation with a moderate heat, and afterwards bruise the remainder and expose it to a stronger heat. The addition of charcoal is useful.

In the Humid Way.

Digest the ore in muriatic acid, adding nitrio by degrees, to help the solution. The sulphur will be found on the filter; the arsenic will remain in the solution, and may be precipitated in its metallic form by boiling with a strip of copper. Nickel Ore.

The ores must be well roasted to expel the sulphur and arsenic; the greener the calx proves during this torrefaction, the more it abounds in the nickel; but the redder it is, the more iron it contains. The proper quantity of this roasted ore is fused in an open crucible, with twice or thrice its weight of black flux, and the whole covered with common salt. By exposing the crucible to the strongest heat of a forge fire, and making the fusion complete, a regulus will be produced. This regulus is not pure, but contains a portion of arsenic, cobalt, and iron. Of the first it may be deprived by a fresh calcination, with the addition of powdered charcoal; and of the second by scorification. But it is with difficulty that it is entirely freed from the iron.

In the Humid Way.

By solution in nitric acid it is freed from its sulphur; and by adding water to the solution, bismuth, if any, may be precipitated; as may silver, if contained it, by muriatic acid; and copper, when any, by iron.

To separate cobalt from nickel, the two oxides are dissolved in muriatic acid; the solution diluted with distilled water. The liquor is saturated with chlorine, and when cold, an excess of precipitated for 18 hours, when the cobalt will be precipitated' carbonate of baryta added. It is then set aside as sesquioxide, while the nickel will remain in solution.

Cobalt Ores.

Free them as much as possible from earthy matnic by roasting. The ore thus prepared is to be ters by well washing, and from sulphur and arse

mixed with 3 parts of black flux, and a little decrepitated sea-salt; put the mixture in a lined crucible, cover it, and place it in a forge-fire, or in a hot furnace, for this ore is very difficult of fusion.

When well fused, a metallic regulus will be found at the bottom, covered with a scoria of a deep blue color; as almost all cobalt ores contain bismuth, this is reduced by the same operation as the regulus of cobalt; but as they are incapable of chemically uniting together, they are always found distinct from each other in the crucible. The regulus of bismuth, having a greater specific gravity, is always at the bottom, and may be separated by a blow with a hammer.

In the Humid Way.

Make a solution of the ore in nitric acid, or

aqua regia, and evaporate to dryness; the residuum, treated with the acetic acid, will yield to it the cobalt; the arsenic should be first precipitated by the addition of water.

Mercurial Ores.

By Cupellation.

the water of the receiver.

Sulphuretted Mercurial Ores.

The sulphurous ores are assayed by distillation in the manner above, only these ores require an equal weight of clean iron-filings to be mixed with them, to disengage the sulphur, while the heat volatilizes the mercury, and forces it into the receiver. These ores should likewise be tried for cinnabar, to know whether it will answer the purpose of extracting it from them; for this a determinate quantity of the ore is finely powdered and put into a glass vessel, which is exposed to a gentle heat at first, and gradually increased till nothing more is sublimed. By the quantity thus acquired, a judgment may be formed whether the process will answer. Sometimes this cinnabar is not of so lively a color as that which is used in trade; in this case it may be refined by a second sublimation, and if it be still of too dark a color, it may be brightened by the addition of a quantity of mercury, and subliming it again.

Humid Assay of Cinnabar. The stony matrix should be dissolved in nitric acid, and the cinnabar being disengaged, should be boiled in 8 or 10 times its weight of aqua regia, composed of 3 parts of nitric, and 1 of muriatic acid. The mercury may be precipitated in the metallic form by zinc.

Silver Ores.

Take the assay quantity of the ore finely powdered, and roast it well in a proper degree of heat, frequently stirring it with an iron rod; then add to it about double the quantity of granulated lead, put it in a covered crucible, and place it in a furnace; raise the fire gently at first, and continue to increase it gradually, till the metal begins to work; if it should appear too thick, make it thinner by the addition of a little more lead; if the metal should boil too rapidly, the fire should be diminished. The surface will be covered by degrees with a mass of scoria, at which time the metal should be carefully stirred with an iron hook heated, especially towards the border, lest any of the ore should remain undissolved; and if what is adherent to the hook when raised from the crucible melts quickly again, and the extremity of the hook, after it is grown cold is covered with a thin, shining smooth crust, the scorification is perfect; but, on the contrary, if, while stirring it, any considerable clamminess is perceived in the scoria, and when it adheres to the hook, though red hot, and appears unequally tinged, and seems dusty or rough, with grains interspersed here and there, the scorification is incomplete; in consequence of which the fire should be increased a little, and what adheres to the hook should be gently beaten off, and returned with a small ladle into the crucible again. When the scorification is perfect, the metal should be poured into a cone, previously rubbed with a little tallow, and when it becomes cold, the scoria may be separated by a few strokes of a hammer. The button is the produce of the assay.

the scoria is formed it will be taken up by the quantity is introduced; then raise the fire, and as cupel, and at last the silver will remain alone. This will be the produce of the assay, unless the lead contains a small portion of silver, which may be discovered by putting an equal quantity of the same lead on another cupel, and working it off at the same time; if any silver be produced it must be deducted from the assay. This is called the

witness.

In the Humid Way — Gay Lussac's Method, Dissolve the ore or coin in nitric acid. Prepare a standard solution of common salt; 542-74 of common salt will precipitate 1000 parts of silver. It is convenient to have, also, solutions of 1-10th the standard strength for the final precipitations. Add the solution until no precipitate appears. From the amount of solution, and consequently of salt used. the amount of silver is at once determined without further weighing. To correct the result a standard silver solution is used at the same time, and any correction it may require is applied to the rest of the assay.

To Assay the Value of Silver.

The general method of examining the purity of silver is by mixing it with a quantity of lead proportionate to the supposed portion of alloy; by remaining button of silver. This is the same protesting this mixture, and afterwards weighing the cess as refining silver by cupellation.

It is supposed that the mass of silver to be examined consists of 12 equal parts, called penny. weights; so that if an ingot weighs 1 oz., each of the parts will be 1-12th oz. Hence, if the mass of silver be pure, it is called silver of 12 dwts.; if it contain 1-12th of its weight of alloy, it is called silver of 11 dwts.; if 2-12ths of its weight be alloy, it is called silver of 10 dwts; which parts of pure silver are called 5 dwts. It must be observed here that assayers give the name dwt. to a weight equal to 24 real grs., which must not be confounded with their ideal weight. The assayers' grs. are called fine grs. An ingot of fine silver, or silver of 12 dwts., contains, then, 288 fine grs.; if this ingot contain 1-288th of alloy, it is said to be silver of 11 dwts. and 23 grs.; if it contain 4-288th of alloy, it is said to be 11 dwts., 20 grs., etc. Now a certain real weight must be taken to represent the assay-weights; for instance, 36 real grs. represent 12 fine dwts. ; this is subdivided into a sufficient number of other smaller weights, which also represent fractions of fine dwts, and grs. Thus, 18 real grs. represent 6 fine dwts; 3 real grs. represent 1 fine dwt., or 24 grs; 14 real grs. represent 12 grs.; 1-32d of a real gr. represents of a fine gr., which is only 1-752d part of a mass of 12 dwt.

Double Assay of Silver.

It is customary to make a double assay. Tho silver for the assay should be taken from opposite sides of the ingot, and tried on a touch stone. Assayers know pretty nearly the value of silver merely by the look of the ingot, and still better by the test of the touch-stone. The quantity of lead to be added is regulated by the portion of alloy, which being in general copper, will be nearly as follows: