ANALYSIS OF ZINC ASH AND CALCINED PYRITES BY MEANS OF AMMONIUM CARBONATE.
In a recent issue of the Chemiker Zeitung Dr. Kosmann has reported an analytical method for the examination of zinciferous products; according to this report, the ash and flue dust produced by the extraction of zinc from its ore comprise:
- Zinc dust, from the distillation of zinc,
- Flue dust, condensed in chambers of zinc furnaces with Kleemann's receivers,
- Zinc ash, of various assortments, from iron blast furnaces.
Of these, zinc dust is the only ready product which is, as color or reducing agent, employed in analytical and technical processes. Its value, when serving the latter purpose, is determined by the percentage of finely divided metallic zinc and cadmium contained therein; of equal reducing power is cadmium, generally associating zinc; injurious, and therefore uneffective, are zinc oxide and oxides of other metals, also metallic lead.
Flue dust, condensed in chambers of zinc furnaces with Kleemann's receivers, is employed with zinc ores in the extraction of zinc, and in small quantities as substitute for zinc white; its commercial value is similarly estimated as that of zinc ores.
The various modifications of zinciferous flue ashes from blast furnaces are an object for continual demand, being both a valuable material for the production of zinc and, in its superior qualities, a desirable pigment. In the regeneration of zinc the presence of foreign substances is of some concern; detrimental are lead, sulphur, and sulphuric acid in form of lead, zinc, and lime sulphate.
The chemico-technical analysis of these products has until recently been confined to the volumetric determination of zinc by means of sodium sulphide (Schaffner's method). But as a remnant of sulphur, as sulphuric acid, in roasted blende causes a material loss during distillation, and otherwise being induced to produce a zinc free of lead, the estimation of sulphur, sulphuric acid, and lead became necessary. These impurities are determined by well-known methods; sulphur is oxidized and precipitated with barium chloride, lead by sulphuric acid and alcohol. The examination of zinc dust, when used for the regeneration of metal, determines the quantity of zinc resident therein, and employed as reducing agent, the quantity of metal which causes the generation of hydrogen. Cadmium, showing the same deportment, must also be considered as well as lead and arsenic.
A most complete and rapidly working method for the examination of zinciferous products has originated with the application of neutral ammonium carbonate as solvent. A solution of this preparation is made, according to H. Rose, by dissolving 230 grm. commercial ammon carbonate in 180 c.c. ammoniacal liquor of 0.92 s.g., and, by addition of water, augmenting it to one liter.
This solution dissolves the metallic components, their oxides, and basic zinc sulphate, and transfers cadmium and lead oxide, also lead, magnesium, and lime sulphate, into insoluble carbonates. Iron and manganese, when present as protoxide, are dissolved; of iron sesquioxide but traces, and of cadmium oxide in statu nascendi a small portion enter into solution. The solution of ammonium carbonate contains in each 10 c.c. 1 grm. ammonia, which dissolves 1.5 grm. zinc.
The sample for examination is moistened with water and mixed with an adequate volume of the solvent, is digested at 50-60° C. until complete decomposition is effected. The heating of the liquid prevents the solution of iron, manganese, and cadmium. The content, sediment and liquid, is thrown on a filter and washed with hot water to which a small quantity of the solvent has been added. When the solution contains iron and manganese, it is separated by decantation from the sediment and oxidized with bromine (according to the method of Nic-Wolff) until a flocculent precipitate of iron sesquioxide and manganese dioxide becomes visible; it is united with the original residue and filtered.
The filtrate is diluted till it appears cloudy, boiled to expel ammonia, tested with sodium sulphide upon the presence of zinc, and, when freed of all zinc, decanted. The precipitate of zinc carbonate is filtered, exhausted with water, transferred into zinc oxide by ignition, and weighed. The gravimetric method can be substituted by the volumetric by introducing a solution of sodium sulphide of known strength into the ammoniacal filtrate. On dividing the filtered liquid into various equal portions other substances, arsenic and sulphuric acid, can be determined from the same sample. For this purpose the filtrate is concentrated; divided into two equal portions, one of which is acidified and treated with hydrogen sulphide for the determination of arsenic, the other is acidified and used for the estimation of sulphuric acid by means of barium chloride. The original residue is dissolved in muriatic or acetic acid and filtered. The lead of the filtered liquid is thrown down by sulphuric acid, and alcohol, and cadmium, after dissipation of alcohol into gas, precipitated by hydrogen sulphide. Iron, manganese, alumina, and other substances present in the solution are determined by known methods.
It is manifest that the determination of substances—zinc, lead, and sulphuric acid—which are of importance in technical analysis of zinc ash, can be executed by this method within a comparatively short time. The application of ammonium carbonate as solvent has the advantage, over the application of ammonia, that it is a far better solvent, that it decomposes insoluble basic sulphates, and that the remaining carbonates are readily dissolved by acids.
The decomposition of zinc dust is accompanied by a lively evolution of gas; it is therefore necessary to continue the digestion of the sample till no more hydrogen is given off. Zinc dust contains both metals and their oxides, and methods which, from the volume of hydrogen generated, determine indirectly the percentage of metallic zinc do not give the real composition of the zinc dust. For the determination of the metallic components the material is digested with a solution of copper sulphate, which dissolves zinc and cadmium; the liquid is filtered, acidified, and decomposed with hydrogen sulphide, or treated with a solution of ammonium carbonate. The use of cupric chloride is not advisable, as it corrodes lead, and gives rise to the formation of soluble chloride of lead, which complicates the separation of zinc from cadmium. The best mode of operation is the following: Both copper sulphate and zinc dust are weighed separately, the former is dissolved in water and the latter introduced into the solution of copper sulphate in small portions until it appears colorless. During the operation the vessel is freely shaken, lumps are comminuted with a glass rod, and a few drops of the liquid are ultimately tested with hydrogen sulphide or ammonia. The remainder of zinc dust is then weighed, and its value deducted from the original weight. Zinc and cadmium of the filtrate are determined as above. On repeating this method several times most satisfactory results are obtained.
Another mode of operating is to employ an excess of copper sulphate and to determine the copper dissolved in the filtrate. The separation of copper from cadmium being difficult and laborious, and the volumetric estimation with potassium cyanide not practicable, it is not prudent to apply this method.
When calcined zinciferous pyrites have to be examined, the estimation of zinc is similar to that employed in the analysis of zinc ore. The sample is exhausted with water, filtered, and, to eliminate calcium sulphate and basic iron sulphate, evaporated to dryness. It is then dissolved in a small quantity of alcohol and water, refiltered, and the filtrate decomposed with ammonium carbonate. The original residue is treated with a solution of ammonium carbonate, which dissolves arsenious acid and basic zinc sulphate, filtered, and united with the first filtrate. When iron and manganese are present, the filtrates are treated with bromine. The united filtrates are boiled or examined volumetrically with sodium sulphide.
PETROLEUM AS FUEL IN LOCOMOTIVE ENGINES.[[2]]
By Mr. THOMAS URQUHART.
Comparing naphtha refuse and anthracite, the former has a theoretical evaporative power of 16.2 lb. of water per lb. of fuel, and the latter of 12.2 lb., at a pressure of 8 atm. or 120 lb. per square inch; hence petroleum has, weight for weight, 33 per cent. higher evaporative value than anthracite. Now in locomotive practice a mean evaporation of from 7 lb. to 7½ lb. of water per lb. of anthracite is about what is generally obtained, thus giving about 60 per cent. efficiency, while 40 per cent. of the heating power is unavoidably lost. But with petroleum an evaporation of 12.25 lb. is practically obtained, giving 12.25/16.2 = 75 per cent. efficiency. Thus in the first place petroleum is theoretically 33 per cent. superior to anthracite in evaporative power; and secondly, its useful effect is 25 per cent. greater, being 75 percent. instead of 60 percent.; while, thirdly, weight for weight, the practical evaporative value of petroleum must be reckoned as at least from (12.25 - 7.50)/7.50 = 63 per cent. to (12.25 - 7.00)/7.00 = 75 per cent. higher than that of anthracite.
Spray injector.—Steam not superheated, being the most convenient for injecting the spray of liquid fuel into the furnace, it remains to be proved how far superheated steam or compressed air is really superior to ordinary saturated steam, taken from the highest point inside the boiler by a special internal pipe. In using several systems of spray injectors for locomotives, the author invariably noticed the impossibility of preventing leakage of tubes, accumulation of soot, and inequality of heating of the fire box. The work of a locomotive boiler is very different from that of a marine or stationary boiler, owing to the frequent changes of gradient on the line, and the frequent stoppages at stations. These conditions render firing with petroleum very difficult; and were it not for the part played by properly arranged brickwork inside the fire box, the spray jet alone would be quite inadequate. Hitherto the efforts of engineers have been mainly directed toward arriving at the best kind of "spray injector," for so minutely subdividing a jet of petroleum into a fine spray, by the aid of steam or compressed air, as to render it inflammable and of easy ignition. For this object nearly all the known spray injectors have very long and narrow orifices for petroleum as well as for steam; the width of the orifices does not exceed from ½ mm. to 2 mm. or 0.02 in. to 0.08 in., and in many instances is capable of adjustment. With such narrow orifices it is clear that any small solid particles which may find their way into the spray injector along with the petroleum will foul the nozzle and check the fire. Hence in many of the steamboats on the Caspian Sea, although a single spray injector suffices for one furnace, two are used, in order that when one gets fouled the other may still work; but, of course, the fouled orifices require incessant cleaning out.
Locomotives.—In arranging a locomotive for burning petroleum, several details are required to be added in order to render the application convenient. In the first place, for getting up steam to begin with, a gas pipe of 1 inch internal diameter is fixed along the outside of the boiler, and at about the middle of its length it is fitted with a three-way cock having a screw nipple and cap. The front end of the longitudinal pipe is connected to the blower in the chimney, and the back end is attached to the spray injector. Then by connecting to the nipple a pipe from a shunting locomotive under steam, the spray jet is immediately started by the borrowed steam, by which at the same time a draught is also maintained in the chimney. In a fully equipped engine shed the borrowed steam would be obtained from a fixed boiler conveniently placed and specially arranged for the purpose of raising steam. In practice steam can be raised from cold water to 3 atm. pressure—45 lb. per square inch—in twenty minutes. The use of auxiliary steam is then dispensed with, and the spray jet is worked by steam from its own boiler; a pressure of 8 atm.—120 lb.—is thus obtained in fifty to fifty-five minutes from the time the spray jet was first started. In daily practice, when it is only necessary to raise steam in boilers already full of hot water, the full pressure of 7 to 8 atm. is obtained in from twenty to twenty-five minutes. While experimenting with liquid fuel for locomotives, a separate tank was placed on the tender for carrying the petroleum, having a capacity of about 3 tons. But to have a separate tank on the tender, even though fixed in place, would be a source of danger from the possibility of its moving forward in case of collision. It was therefore decided, as soon as petroleum firing was permanently introduced, to place the tank for fuel in the tender between the two side compartments of the water tank, utilizing the original coal space. For a six-wheeled locomotive the capacity of the tank is 3½ tons of oil—a quantity sufficient for 250 miles, with a train of 480 tons gross exclusive of engine and tender. In charging the tender tank with petroleum, it is of great importance to have strainers of wire cloth in the manhole of two different meshes, the outer one having openings, say, of ¼ in., the inner, say ⅛ in.; these strainers are occasionally taken out and cleaned. If care be taken to prevent any solid particles from entering with the petroleum, no fouling of the spray injector is likely to occur; and even if an obstruction should arise, the obstacle being of small size can easily be blown through by screwing back the steam cone in the spray injector far enough to let the solid particles pass and be blown out into the fire-box by the steam. This expedient is easily resorted to even when running; and no more inconvenience arises than an extra puff of dense smoke for a moment, in consequence of the sudden admission of too much fuel. Besides the two strainers in the manhole of the petroleum tank on the tender, there should be another strainer at the outlet valve inside the tank, having a mesh of ⅓ in. holes.
Driving locomotives.—In lighting up, certain precise rules have to be followed, in order to prevent explosion of any gas that may have accumulated in the fire box. Such explosions do often take place through negligence; but they amount simply to a puff of gas, driving smoke out through the ash-pan dampers, without any disagreeably loud report. This is all prevented by adhering to the following simple rules: First clear the spray nozzle of water by letting a small quantity of steam blow through, with the ash-pan doors open; at the same time start the blower in the chimney for a few seconds, and the gas, if any, will be immediately drawn up the chimney. Next place on the bottom of the combustion chamber a piece of cotton waste, or a handful of shavings saturated with petroleum and burning with a flame. Then by opening first the steam valve of the spray injector, and next the petroleum valve gently, the very first spray of oil coming on the flaming waste immediately ignites without any explosion whatever; after which the quantity of fuel can be increased at pleasure. By looking at the top of the chimney, the supply of petroleum can be regulated by observing the smoke. The general rule is to allow a transparent light smoke to escape, thus showing that neither too much air is being admitted nor too little. The combustion is quite under the control of the driver, and the regulation can be so effected as to prevent smoke altogether. While running, it is indispensable that the driver and fireman should act together, the latter having at his side of the engine the four handles for regulating the fire, namely, the steam wheel and the petroleum wheel for the spray injector, and the two ash-pan door handles in which there are notches for regulating the air admission. Each alteration in the position of the reversing lever or screw, as well as in the degree of opening of the steam regulator or the blast pipe, requires a corresponding alteration of the fire. Generally the driver generally passes the word when he intends shutting off steam, so that the alteration in the firing can be effected before the steam is actually shut off; and in this way the regulation of the fire and that of the steam are virtually done together. All this care is necessary to prevent smoke, which is nothing less than a waste of fuel. When, for instance, the train arrives at the top of a bank, which it has to go down with the brakes on, exactly at the moment of the driver shutting off the steam and shifting the reversing lever into full forward gear, the petroleum and steam are shut off from the spray injector, the ash-pan doors are closed, and if the incline be a long one, the revolving iron damper over the chimney top is moved into position, closing the chimney, though not hermetically. The accumulated heat is thereby retained in the fire-box; and the steam even rises in pressure, from the action of the accumulated heat alone. As soon as the train reaches the bottom of the incline and steam is again required, the first thing done is to uncover the chimney top; then the steam is turned on to the spray injector, and next a small quantity of petroleum is admitted, but without opening the ash-pan doors, a small fire being rendered possible by the entrance of air around the spray injector, as well as by possible leakage past the ash-pan doors. The spray immediately coming in contact with the hot chamber ignites without any audible explosion; and the ash-pan doors are finally opened, when considerable power is required, or when the air otherwise admitted is not sufficient to support complete combustion. By looking at the fire through the sight hole it can always be seen at night whether the fire is white or dusky; in fact, with altogether inexperienced men it was found that after a few trips they could become quite expert in firing with petroleum. The better men contrive to burn less fuel than others, simply by greater care in attending to all the points essential to success. At present seventy-two locomotives are running with petroleum firing; ten of them are passenger engines, seventeen are eight-wheel coupled goods engines, and forty-five are six-wheel coupled. As might be expected, several points have arisen which must be dealt with in order to insure success. For instance, the distance ring between the plates around the firing door is apt to leak, in consequence of the intense heat driven against it, and the absence of water circulation; it is therefore either protected by having the brick arch built up against it, or, better still, it is taken out altogether when the engines are in for repairs, and a flange joint is substituted, similar to what is now used in the engines of the London and Northwestern Railway. This arrangement gives better results, and occasions no trouble whatever.
Storage of petroleum.—The length of line now worked with petroleum is from Tsaritsin to Burnack, 291 miles. There is a main iron reservoir for petroleum at each of the four engine sheds, namely at Tsaritsin, Archeda, Filonoff, and Borisoglebsk. Each reservoir is 66 ft. internal diameter and 24 ft. high, and when full holds about 2,050 tons. The method of charging the reservoir, which stands a good way from the line, and is situated at a convenient distance from all dwelling houses and buildings, is as follows: On a siding specially prepared for the purpose are placed ten cistern cars full of oil, the capacity of each being about ten tons. From each of these cars a connection is made by a flexible India rubber pipe to one of ten stand pipes which project 1 ft. above the ground line. Parallel with the rails is laid a main pipe, with which the ten stand pipes are all connected, thus forming one general suction main. About the middle of the length of the main, which is laid underground and covered with sawdust or other non-conducting material, is fixed a Blake steam pump. As soon as all the ten connections are made with the cistern cars, the pump is set to work, and in about one hour the whole of the cars are discharged into the main reservoir, the time depending of course upon the capacity of the pump. All the pipes used are of malleable iron, lap-welded, and of 5 in. internal diameter, having screwed coupling muffs for making the connections. At each engine shed, in addition to the main storage reservoir, there is a smaller distributing tank, which is erected at a sufficient height to supply the tenders, and very much resembles the ordinary water tanks. These distributing tanks are circular, about 8½ ft. diameter and 6 ft. high, and of ¼ in. plates; their inside mean area is calculated exactly, and a scale graduated in inches stands in the middle of the tank; a glass with scale is used outside in summer time. Each inch in height on the scale is converted into cubic feet, and then by means of a table is converted into Russian poods, according to the specific gravity at various temperatures. As it would be superfluous to graduate the table for each separate degree of temperature, the columns in the table show the weights for every 8 degrees Reaumur, which is quite sufficient: namely, from 24 deg. to 17 deg., from 16 deg. to 9 deg., and so on, down to -24 deg.; the equivalent Fahrenheit range being from 86 deg. down to -22 deg. Suppose the filling of a tender tank draws off a height of 27 in. from the distributing tank, at a temperature of say -20 deg. R., these figures are shown by the table to correspond with 200.61 poods = 7,245 lb., or 3.23 tons, of petroleum. This arrangement does very well in practice; both the quantity and the temperature are entered on the driver's fuel bill at the time of his taking in his supply.
Engines.—The engines used in the trials were built by Borsig, of Berlin, Schneider, of Creusot, and the Russian Mechanical and Mining Company, of St. Petersburg. Their main dimensions and weights were about the same, as follows, all of them having six wheels coupled, and 36 tons adhesive weight; as originally constructed they had ordinary fire boxes for burning anthracite or wood; cylinders 18⅛ in. diameter and 24 in. stroke; slide valves, outside lap 1-1/16 in., inside lap 3/32 in., maximum travel, 4-9/16 in.; Stephenson link motion; boiler pressure, 120 lb. per square inch; six wheels, all coupled, 4 ft. 3 in. in diameter; distance between centers of leading and middle wheels, 6 ft. 2¾ in.; between middle and trailing, 4 ft. 9¼ in.; total length of wheel base, 11 ft.; weight empty, on leading wheels, 12.041 tons; middle, 10.782 tons; trailing, 10.685 tons; total weight, 33.508 tons empty; weight in running order, on leading wheels, 12.563 tons; middle, 11.885 tons; trailing 12.790 tons; total weight, 37.238 tons in running order. Tubes number 151; outside diameter, 2⅛ in.; length between tube plates, 13 ft. 10⅛ in.; outside heating surface, 1,166 square feet; fire box heating surface, 82 square feet; total heating surface, 1,248 square feet; fire grate area, 17 square feet;tractive power = 65 per cent. of boiler pressure × (cyl. diam.)² × stroke / diameter of wheels = 0.65 × 120 × (18.125)² × 24 / 51 = 5.383 tons. Ratio of tractive power to adhesion weight = 5.383 / 37.238 = 1 / 6.9.
Tender.—Contents: water, 310 cubic feet, or 1,933 gallons, or 8½ tons; anthracite, 600 poods, or 10 tons; or wood, 1½ cubic sajene, or 514 cubic feet; weight empty, 13.477 tons; weight in running order, 28.665 tons; six wheels.
Petroleum Refuse—Comparative Trials with Petroleum, Anthracite, Bituminous Coal, and Wood, between Archeda and Tsaritsin on Grazi and Tsaritsin Railway, in Winter Time.
-----+----+-----+------+---+-----+------+-----------+-------------+------+------------
| L | | | | | | | |
| o | | Train | | | | Consumption | |
| c | | alone. | | | | Including | |
Date.| o | | | | | | Lighting up.| |
1883.| m | |----+-----| | | | | Cost |
| o |Train|Num-| | Dis-| Car | | | of |Atmospheric
| t | |ber |Gross|tance|miles.| Fuel. |-------+-----| fuel |temperature
| i | | of |load.| run.| | | | Per | per | and
| v | |Loa-| | | | | Total |train| train| weather.
| e | |ded | | | | | |mile.| mile.|
| . | |cars| | | | | | | |
-----+----+-----+----+-----+-----+------+-----------+-------+-----+------+------------
| | | No.| Tons|Miles| | | | |Pence.|
-----+----+-----+----+-----+-----+------+-----------+-------+-----+------+------------
| 8 |32-23| 25 | 400 | 388 | 9,700|Anthracite.| 31799 |81.90|11.957|-17° to -18°
| |32-23| | | | | | lb. | lb. | | Reau.,
Feb.| | | | | | | | | | | equiv. to
8 | |24-21| | | | | | | | |-6° to -8½°
| 14 |24-21| 25 | 400 | 388 | 9,700|Bituminous |37557.5|96.53|14.093| Fah.
| | | | | | | Coal. | lb. | lb. | |
| 7 |26-29| 25 | 400 | 194 | 4,830|Petroleum | 9462 |48.77| 5.487| Strong
| | | | | | refuse. | lb. | lb. | | side wind.
-----+----+-----+----+-----+-----+------+-----------+-------+-----+------+------------
| 24 |32-23| 25 | 400 | 194 | 4,850|Anthracite.|12639.5|65.15| 9.512|-5° to -9°
March| | | | | | | | lb. | lb. | | Reau.,
6 | 21 |24-21| 25 | 400 | 194 | 4,850|Wood, in | 1071.8| 5.52| 8.5 | equiv. to
| | | | | | | billets. | c. ft.|c. ft| | 21° to 12°
| | | | | | | | | Fah.
| 23 |26-27| 25 | 400 | 194 | 4,850|Petroleum | 7228 |37.28| 4.188| Light
| | | | | | refuse. | lb. | lb. | | side wind.
-----+----+-----+----+-----+-----+------+-----------+-------+-----+------+-----------
Prices of fuel:
Petroleum refuse, 21s. per ton; Anthracite and bituminous coal, 27s. 3d. per ton;
Wood, in billets, 42s. per cubic sajene = 343 cubic feet;
equivalent to 1.47d. per cubic foot.
Dimensions of locomotives:
Cylinders, 18 ⅛ in. diam. and 24 in. stroke; Wheels, 4 feet 3 in. diam.;
Total heating surface, 1,248 sq. feet: Total adhesion weight, 36 tons;
Boiler pressure, 8 to 9 atm.
The preceding table shows the results of comparative trials made in winter with different sorts of fuel, under exactly similar conditions as to type of engine, profile of line, and load of train. Two sets of comparative trials were made, both of them in winter. The three engines used were some of those built by Schneider. In comparison with anthracite, the economy in favor of petroleum refuse was 41 per cent. in weight, and 55 per cent. in cost. With bituminous coal there was a difference of 49 per cent. in favor of petroleum as to weight and 61 per cent. as to cost. As compared with wood petroleum was 50 per cent. cheaper. At a speed of fourteen miles an hour up an incline of 1 in 125 the steam pressure was easily kept up at 9 to 9½ atm. with a No. 9 injector feeding the boiler all the time.
Up to the present time the author has altered seventy-two locomotives to burn petroleum; and from his own personal observations made on the foot plate with considerable frost he is satisfied that no other fuel can compare with petroleum either for locomotives or for other purposes. In illustration of its safety in case of accident, a photograph was exhibited of an accident that occurred on the author's line on 30th December, 1883, when a locomotive fired with petroleum ran down the side of an embankment, taking the train after it; no explosion or conflagration of any kind took place under such trying circumstances, thus affording some proof of the safety of the petroleum refuse in this mode of firing. Although it is scarcely possible that petroleum firing will ever be of use for locomotives on the ordinary railways of coal-bearing England, yet the author is convinced chat, even in such a country, its employment would be an enormous boon on underground lines.
Abstract of paper read before the Institution of Mechanical Engineers.