Chapter 2

Fine pulverization of the sample is not essential, and in fact is rather detrimental, as the graphite, when fine, is more difficult to wash without loss. When operating on a coarse sample more time is necessarily taken, but the resulting graphite shows the manner of occurrence better, whether in scales or in the amorphous form.

In consulting the literature bearing on the subject, I cannot find any mention of this method employed as an analytical process; it has, however, been previously described as a commercial method for the purification of graphite,[1] and I understand has been tried on a small scale in this country. The method, though inexpensive, yet seems to have been abandoned for some reason, and I am not aware that it is now employed anywhere.--_Sch. Mines Quarterly._

[Footnote 1: Schloffel, Zeitschrift der K.K. geolog. Reichanstalt, 1866, p. 126.]

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SULPHOCYANIDE OF POTASSIUM.

The elements of cyanogen, combined with sulphur, form a salt radical, sulphocyanogen, C_{2}NS_{2}, which is expressed by the symbol Csy. The sulphocyanide of potassium, KCsy, is prepared by fusing ferrocyanide of potassium, deprived of its water of crystallization, intimately mixed with half its weight of sulphur and 17 parts of carbonate of potassa. The molten mass, after having cooled, is exhausted with water, the solution evaporated to dryness, and extracted with alcohol, from which the crystals of the salt are separated by evaporation.

It is also made by melting the ferrocyanide of potassium with sulphide of potassium. It is a white, crystallizable salt of a taste resembling that of niter, soluble in water and alcohol, and extremely poisonous. It dissolves the chlorides, iodides, and bromides of silver, is, therefore, a fixing agent, but has not come in general use as such. Vogel speaks highly of it as an addition to the positive toning bath, although he prefers the analogous ammonium salt in the following formula:

Chloride of gold solution.... (1:50) 3 c. cm. (46-1/5 grains). Sulphocyanide of ammonium ... 20 grammes (308 grains). Water........100 c. cm. (3 ounces 5 drachms 40 grains).

_Ferrocyanide of Potassium_--K_{2}Cfy+3HO, or K_{2}C_{8}N_{3}Fe+3HO, is generally known by the name of yellow prussiate of potassa. It contains ferrocyanogen, a compound radical, consisting of 1 eq. of metallic iron and 3 eq. of the elements of cyanogen, and is designated by the symbol Cfy.

The potassium salt is manufactured on a large scale from refuse animal matter, as old leather, chips of horn, woolen rags, hoofs, blood (hence its German name, "Blutlaugen salz"), greaves, and other substances rich in nitrogen, by fusing them with crude carbonate of potassa and iron scraps or filings to a red heat, the operation to go on in an iron pot or shell, with the exclusion of all air. Cyanide of potassium is generated in large quantities. The melted mass is afterward treated with hot water, which dissolves the cyanide and other salts, the cyanide being then quickly converted by the action of oxide of iron, formed during the operation of fusing, into ferrocyanide. The filtered solution is evaporated, crystallized, and recrystallized. The best temperature for making the solution is between 158 and 176 deg. F. The conversion of the cyanide into the ferrocyanide is greatly facilitated by the presence of finely divided sulphuret of iron and caustic potash. Some years ago this salt was manufactured by a process which dispensed with the use of animal matter, the necessary nitrogen being obtained by a current of atmospheric air. Fragments of charcoal, impregnated with carbonate of potassa, were exposed to a white heat in a clay cylinder, through which a current of air was drawn by a suction pump. The process succeeded in a chemical sense, but failed on the score of economy.

Richard Brunquell passes ammonia through tubes filled with charcoal, and heated to redness so as to form cyanide of ammonium, which is converted into the ferrocyanide of potassium by contact with potash solution and suitable iron compounds. Ferrocyanide of potassium is in large beautiful transparent four-sided tabular crystals, of a lemon-yellow color, soluble in four parts of cold and two of boiling water, insoluble in alcohol. Exposed to heat it loses three eq. of water, and becomes anhydrous; at a high temperature it yields cyanide of potassium, carbide of iron, and various gases. This salt is said to have no poisonous properties, although the dangerous hydrocyanic acid is made from it. In large doses it occasions, however, vertigo, numbness, and coldness. It is used in various photographic processes. Newton employs it in combination with pyrogallol and soda in the development of bromo-gelatine plates.

The ferri or ferrid cyanide of potassium discovered by Gmelin is often, but improperly, termed red prussiate of potash. It is formed by passing a current of chlorine gas through a solution of ferrocyanide of potassium until the liquid ceases to give a precipitate with a salt of sesquioxide of iron, and acquires a deep, reddish-green color. The solution is then evaporated, crystallized, and recrystallized. It forms regular prismatic or tabular crystals, of a beautiful ruby-red tint, permanent in the air, soluble in four parts of cold water. The crystals burn when introduced into the flame of a candle, and emit sparks.

The theory of the formation of this salt is, that one eq. of chlorine withdraws from two eq. of the ferrocyanide of potassium, one eq. of potassium, forming chloride of potassium, which remains in the mother liquid. The reaction is explained by the following equation: 2(K_{2}Cfy)+Cl=K_{3}Cfy_{2}+KCl.

The radical ferridcyanogen, isomeric[2] with ferrocyanogen, is supposed to be formed by the coalescence of two equivalents of ferrocyanogen, and is represented by the symbol Cfdy; accordingly the formula of ferridcyanide of potassium is K_{3}Cfdy.

[Footnote 2: Isomeric bodies, or substances different in properties yet identical in composition, are of constant occurrence in organic chemistry, and stand among its most peculiar features.]

Ferridcyanide of potassium has found extensive application in photographic processes for intensifying negatives; those of Eder, in combination with nitrate of lead, or Selle's, with nitrate of uranium; Ander's blue intensification of gelatine negatives, Farmer's process of reducing intensity, the coloring of diapositives, the very important blue printing, and various others, are daily practiced in our laboratories.

The ferrocyanide of potassium is a chemical reagent of great value, giving rise to precipitates with the neutral or slightly acid solutions of metals, like the beautiful brown ferrocyanide of copper, and that of lead. When a ferrocyanide is added to a solution of a sesquioxide of iron, Prussian blue or ferrocyanide of iron is produced. The exact composition of this remarkable substance is not distinctly stated, as various blue compounds may be precipitated under different circumstances. Berzelius gives the following account: 3 eq. of ferrocyanide and 2 eq. of sesquioxide of iron are mutually decomposed, forming 1 eq. of Prussian blue and 6 eq. of the potassa salt, which remains in solution, or 3K_{2}Cfy + 2(Fe_{2}O_{3}3NO_{3}) = Fe_{4}Cfy_{3} + 6(KO,NO_{5}). It forms a bulky precipitate of an intense blue, is quite insoluble in water or weak acids, with the exception of oxalic acid, with which it gives a deep blue liquid, occasionally used as blue ink.

Ferridcyanide of potassium, added to a salt of the sesquioxide of iron, yields no precipitate, but merely darkens the reddish-brown solution; with protoxide of iron it gives a blue precipitate, containing Fe_{3}Cfdy, which is of a brighter tint than that of Prussian blue, and is known by the name of Turnbull's blue. Hence, the ferridcyanide of potassium is as excellent a test for protoxide of iron as the yellow ferrocyanide is for the sesquioxide.--_E., Photo. Times_.

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FOUCAULT'S APPARATUS FOR MANUFACTURING ILLUMINATING GAS AND HYDROGEN.

The illuminating gas and hydrogen apparatus, illustrated herewith, is adapted to all cases in which it is desirable to manufacture gas upon a small scale.

Through the use solely of oil or water, it produces illuminating gas or pure hydrogen for all the applications that may be required of them. It consists of three parts, viz., of a vaporizer, A, which converts the liquids into gas; of a distributer, B, which contains and distributes the liquids to be converted into gas, and of a regulator, C, which automatically regulates the flow of the liquids in proportion as they are used.

In the vaporizer Mr. Foucault, the inventor of the apparatus, obtains a perfectly regular combustion through the use of a central column, 15, charged with fuel, closed at the upper part, open beneath, and entering a furnace that is fed by it with regularity, the zone of combustion not being able to extend beyond the level of the draught. The grate, 16, is capable of revolving upon its axis in order to separate the cinders. It also oscillates, and is provided with jaws for crushing the fuel; and it may likewise be lowered so as to let the fire drop into the ash-pan when it is desired to stop operations.

The vaporizer, properly so called, is not placed directly over the fire, and for this reason the production of a spheroidal state of the liquid is avoided. It consists of a vessel, 44, into which the liquid is led by a pipe, 43. The cast-iron evaporating vessel, 14, is provided with appendages, 14 _bis_, which dip into the liquid and bring about its evaporation. A refractory clay sleeve, 41, protects the lower part of the cylinder, 15, from the fire, and diminishes the smoke passages at 42. The vapor produced makes its way vertically through a layer of charcoal placed between the evaporating vessel, 14, and the receiver, 17, and serving to decompose the aqueous vapor formed.

All clay and red and white lead joints are done away with in this part of the apparatus, as are also packing bolts. Thus, at the upper part the cover, 19, is provided with a rim that enters a cavity filled with lead, so, too, the lower part of the evaporating vessel, 14, rests in a channel containing lead. There is also at 30, a joint of the same character for the rim of the external cylindrical vessel, 18. Both this latter and the receiver, 17, dip beneath into a tank of water, 66.

The distributer, B, is so arranged as to cause the water, and oil, and the liquids to be vaporized to flow with the greatest regularity, and proportionally to the consumption of the gas in cases where the latter is not stored up in a gas meter. The flow is controlled by cocks that are actuated by variations in the height of the regulator receiver. All the condensation that occurs in the various parts of the apparatus collects in a receptacle, 52, so arranged as to perform the office of a separator and set apart the oil at 20, and the water at 21, through the natural effect of their difference in density. This latter is likewise utilized for causing the oil to flow into the vaporizer through 26 and 27, instead of using a graduated cock that receives a variable pressure from the receiver. In this way every cause of obstruction is avoided.

We have stated that the regulator, C, serves to automatically regulate the flow of the liquids proportionally to the consumption of the gases produced. To effect this a communication is established between the regulator receiver, 59, and the aperture through which the liquids flow, and the flow is thus modified by the valves, 54 and 55.

The water contained in the reservoir of the regulator serves to wash the gas which enters through a number of orifices in the disk, 60, this latter being fixed beneath the level of the water. The gas may be purified by dissolving metallic salts in the water.

By means of the arrangement above described, there may be manufactured at will a rich gas from liquid hydrocarburets, hydrogen from water, and gas obtained by an admixture of two others simultaneously produced and combined in the apparatus.--_Chronique Industrielle._

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SUGAR NITRO-GLYCERINE.

A new explosive has been discovered by M. Roca, a French engineer, who communicates an account of it to _Le Génie Civil_. The discovery was due entirely to scientific induction from some experiments made upon different specimens of dynamite, with a view to the determination of the effect on the explosive force of the various inert or at least slowly combustible substances with which nitro-glycerine is mixed to produce the dynamite of commerce. Of late, in place of the infusorial earth which formed the solid portion of Nobel's dynamite, such substances as sawdust, powdered bark, and even gunpowder, have been used, probably for the sake of economy alone, without, except in the latter case, any reference to the influence which they might have upon the combustion of the nitro-glycerine; but M. Roca, in testing a variety of samples, was struck by the difference among them in regard to energy of explosion, and discovered that if a portion of free carbon, sufficient to combine with the oxygen disengaged from the nitro-glycerine, was present at the moment of detonation, the effect was greater than where, as in the case of gunpowder, the solid portion alone furnished oxygen enough to burn all the free carbon, without calling upon the nitro-glycerine for any. In fact, it appeared from experiment that the dose of carbon might with advantage be so great as not only to be itself oxidized into carbonic oxide by the oxygen of the nitro-glycerine, but to reduce the carbonic acid developed by the explosion of the latter itself into carbonic oxide. The limit of the advantageous effect of free carbon ceased here, and if more were added to the mixture, the cavities formed by the explosion in the lead cubes used for test were found simply lined with soot; but up to the limit necessary for converting all the carbon in the dynamite into carbonic oxide, the addition of a reducing agent was shown to be an important gain. This was confirmed by theory, which shows that pure nitro-glycerine, which is composed of six parts of carbon and two of hydrogen, combined with three times as much nitric acid and water, decomposes on explosion into six parts of carbonic acid, five of watery vapor, one of oxygen, and three of nitrogen, while the addition of seven more parts of free carbon to the mixture causes the development, by explosion, of thirteen volumes of carbonic oxide, five parts of watery vapor, and three of nitrogen, or twenty-one volumes of gas in place of fifteen. As the power of an explosive depends principally on the amount of gas which results from its sudden combustion, it was evident that the addition of pure or nearly pure carbon, in a condition to be readily combined with the other elements, ought to increase materially the force of nitro-glycerine, and M. Roca experimented accordingly with an admixture of sugar, as a highly carbonized body immediately available, and found that three parts of this, mixed with seven parts of nitro-glycerine, detonated with a force from thirty to thirty-five per cent. greater than that of pure nitro-glycerine. Many other organic carbonaceous substances may be employed in place of sugar, with various advantages. In comparing these simple compounds with the celebrated explosive gum, prepared by dissolving gun-cotton in nitro-glycerine, it is found that the latter is far inferior, having an energy very little superior to that of pure nitro-glycerine.

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THE CIRCLE-DIVIDER.

This little apparatus, invented by Prof. Mora, of Senlis, permits of dividing circumferences or circles into equal or proportional parts. It consists (Fig. 2) of a rule, A, divided into equal or proportional parts, which pivots in the manner of a compass around a rod, T, that serves as a central rotary point. Along this rule moves a slide, R, provided with an aperture, C, which is made to coincide with one of the divisions. This division corresponds to the number of equal or proportional parts into which the circle is to be divided. The slide is provided with a wheel, E, that carries a point which serves at every revolution to trace the points that indicate the divisions of the circumference.

The apparatus operates as follows: Suppose, for example, that it becomes necessary to divide a circumference into 19 equal parts: We make the aperture, C, coincide with the 19th division of the rule, and fix the point of the rod, T, in the center of the circumference, and cause the rule to revolve around it. The wheel, E, will revolve upon its axis, g, and, at every revolution, its point will make a mark which corresponds to the 19th part of the circumference--

Circumf. c / Circumf. C = r / R

It is always necessary that the extremity of the wheel, E, and the center-point, T, shall be at the same height in order to have the divisions very accurate.

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SOLUBLE GLASS.

Although the manufacture of soluble glass does not strictly belong to the glass maker's art, yet it is an allied process to that of manufacturing glass. Of late soluble glass has been used with good effect as a preservative coating for stones, a fire-proofing solution for wood and textile fabrics. Very thin gauze dipped in a solution of silicate of potash diluted with water, and dried, burns without flame, blackens, and carbonizes as if it were heated in a retort without contact of air. As a fire-proofing material it would be excellent were it not that the alkaline reaction of this glass very often changes the coloring matters of paintings and textile fabrics. Since soluble glass always remains somewhat deliquescent, even though the fabrics may have been thoroughly dried, the moisture of the atmosphere is attracted, and the goods remain damp. This is the reason why its use has been abandoned for preserving theater decorations and wearing apparel. Another application of soluble glass has been made by surgeons for forming a protecting coat of silicate around broken limbs as a substitute for plaster, starch, or dextrine.

The only use where soluble glass has met with success is in the preservation of porous stones, building materials, paintings in distemper, and painting on glass. Before we describe these applications, we will give the processes used in making soluble glass.

The following ingredients are heated in a reverberatory furnace until fusion becomes quieted: 1,260 pounds white sand, 660 pounds potash of 78°. This will produce 1,690 pounds of transparent, homogeneous glass, with a slight tinge of amber. This glass is but little soluble in hot water. To dissolve it, the broken fragments are introduced into a iron digester charged with a sufficient quantity of water, at a high pressure, to make a solution marking 33° to 35° Baume. Distilled or rain water should be used, as the calcareous salts contained in ordinary water would produce insoluble salts of lime, which would render the solution turbid and opalescent; this solution contains silica and potash combined together in the proportion of 70 to 30.

Silicate of soda is made with 180 parts of sand, 100 parts carbonate of soda (0.91), and is to be melted in the same manner as indicated previously.

Soluble glass may also be prepared by the following method: A mixture of sand with a solution of caustic potash or soda is introduced into an iron boiler, under 5 or 6 atmospheres of pressure, and heated for a few hours. The iron boiler contains an agitator, which is occasionally operated during the melting. The liquid is allowed to cool until it reaches 212°, and is drawn out after it has been allowed to clear by settling; it is then concentrated until it reaches a density of 1.25, or it may be evaporated to dryness in an iron kettle. The metal is not affected by alkaline liquors.

The glass is soluble in boiling water; cold water dissolves but little of it. The solution is decomposed by all acids, even by carbonic acid. Soluble glass is apparently coagulated by the addition of an alkaline salt; mixed with powdered matters upon which alkalies have no effect, it becomes sticky and agglutinative, a sort of mineral glue.

To apply soluble glass for the preservation of buildings and monuments of porous materials, take a solution of silicate of potash of 35° Baume, dilute it with twice its weight of water, paint with a brush, or inject with a pump; give several coats. Experience has shown that three coats applied on three successive days are sufficient to preserve the materials indefinitely, at a cost of about 15 cents per square yard. When applied upon old materials, it is necessary to wash them thoroughly with water. The degree of concentration of the solutions to be used varies with the materials. For hard stones, such as sand and free stones, rock, etc., the solution should mark 7° to 9° Baume; for soft stones with coarse grit, 5° to 7°; for calcareous stones of soft texture, 6° to 7°. The last coating should always be applied with a more dilute solution of 3° to 4° only.

Authorities are divided upon the successful results of the preservation of stone by silicates. Some claim in the affirmative that the protection is permanent, while others assert that with time and the humidity of the atmosphere the beneficial effects gradually disappear. It might be worth while to experiment upon some of the porous sandstones, which, under the extreme influence of our climate, rapidly deteriorate; such, for instance, as the Connecticut sandstone, so popular at one time as a building material, but which is now generally discarded, owing to its tendency to crumble to pieces when exposed to the weather even for a few years.

Soluble glass has also been used in Germany to a great extent for mural painting, known as stereochromy. The process consists in first laying a ground with a lime water; when this is thoroughly dry, it is soaked with a solution of silicate of soda. When this has completely solidified, the upper coating is applied to the thickness of about one-sixteenth of an inch, and should be put on very evenly. It is then rubbed with fine sandstone to roughen the surface. When thoroughly dry, the colors are applied with water; the wall is also frequently sprinkled with water. The colors are now set by using a mixture of silicate of potash completely saturated with silica, with a basic silicate of soda (a flint liquor with soda base, obtained by melting 2 parts sand with 3 parts of carbonate of soda). As the colors applied do not stand the action of the brush, the soluble glass is projected against the wall by means of a spray. After a few days the walls should be washed with alcohol to remove the dust and alkali liberated.

The colors used for this style of painting are zinc white, green oxide of chrome, cobalt green, chromate of lead, colcothar, ochers, and ultramarine.

Soluble glass has also been used in the manufacture of soaps made with palm and cocoanut oil; this body renders them more alkaline and harder.

Interesting experiments have been made with soluble glass for coloring corals and shells. By plunging silicated shells into hot solutions of salts of chrome, nickel, cobalt, or copper, beautiful dyes in yellow, green, and blue are produced. Here seems to be a field for further application of this discovery.