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INDUSTRIAL AND ENGINEERING CHEMISTRY
perience to sharpen properly and keep the knife in condition. These considerations have led the present writers to publish the result of a study of the polishing methods that has been in progress for some time, and in which has been developed a technic that is rapid, can be successfully carried out with any polishing equipment, and leads to the formation of ideal surfaces for microscopical examination. Figures 11, 12, 13, and 14 illustrate the appearance of the structures of a 1 per cent antimony-lead alloy after various treatments, as developed by the methods of polishing and etching described here. Figures 15 and 16 illustrate the structure of a 3 per cent tin-lead alloy as developed by the same process. The time required to prepare a sample depends entirely
Vol. 19, No. 9
on the skill of the operator, an experienced one being able to complete the entire operation in less than an hour. The structure of properly prepared samples can be easily developed in 10 seconds, even when employing as slow an acting reagent as that previously described. It is by no means necessary to etch deeply in order to get below polishing imperfections. The fact that the blackening often observed during the polishing operation can be avoided by careful manipulation or removed, when it appears, by gentle polishing on a very wet cloth, seems to indicate that its cause is other than oxidation due to the polishing operation. It has been observed that a polished specimen of lead will retain its bright surface for several days.
Total Carbon in Coal’ Determined by Analysis of Gas from Bomb Calorimeter By Geo. B. Watkins DEPARTMENT OF CHEMICAL ENGINEERING, UNIVERSITY OF MICHIGAN. ANN ARBOR,MICH.
A mercury-sealed gasometer suitable for measuring ard for the determination of HEAT balance on furthe volume of the gaseous products of combustion from carbon and hydrogen in ornaces u s i n g f u e l t o heating value determinations of coal and combustible ganic compounds and fuels.2 supply the heat energy organic compounds is described. The carbon dioxide While this method gives requires a material balance. content of these products is determined and the total excellent results when used by A material balance requires carbon calculated. skilled and competent chemthe measurement of either the Five different coal samples and benzoic acid and suists in laboratories especially air or fuel entering the furcrose were exploded in a bomb and temperature-time equipped for the study of nace and the analysis of the readings necessary for heating value calculations refuels, it is unreliable when products of combustion. The corded. The products of combustion were then reused under adverse circumanalysis of the combustion leased into the gasometer and their volume was measstances. For t h i s r e a s o n products is relatively simple. ured at about atmospheric pressure. Samples of gas numerous attempts have been A direct measurement of the were withdrawn from the gasometer and carbon dimade to replace it by a simair required for combustion oxide was determined by absorption in caustic solution. p l e r a n d m o r e expeditious is practically irnpossiblc since The total carbon of the coals calculated from these method. the air usually enters the furdata checks the Bureau of Mines value within oneG o u t a l determines the nace a t many points. The tenth of one per cent. The time required for the total t o t a l c a r b o n in coals by choice of methods for making carbon determination is less than one-half hour after exploding the sample in a t h e m a t e r i a l and the heat the completion of the heating value test. b o m b s i m i l a r in design to b a l a n c e on the furnace is the one proposed by KroLker.‘ therefore limited to the measThe bomb has a capacity of approximately 100 cc. and is urement and analysis of fuel input. The actual analytical data relative to fuels, and neces- equipped with two needle valves, placed half way up and sary for making a material and heat balance, are the heating diametrically opposite. The products of combustion are exvalue, moisture, ash, and total carbon. While the first three panded into a special absorption apparatus containing caustic determinations are relatively short and simple, the recog- solution, and the carbon dioxide is determined by titrating nized standard method for total carbon determination is the excess alkali with standard acid. This method is said to slow and tedious, requiring expensive apparatus and skilful be accurate within 0.3 per cent. Parr’s6 method for estimating the total carbon in coal is manipulation. The methods for determining total carbon in organic com- an example of the second class, in which oxygen other than pounds and fuels all involve the oxidation of the carbon with molecular is used to oxidize the carbon. The method consubsequent determination of the carbon dioxide formed. sists in utilizing the residue from the sodium peroxide fusion The methods may be divided roughly into two classes: (1) in which the total carbon of the coal has been oxidized and those using molecular oxygen to complete the oxidation, and combined with the chemical to form sodium carbonate. The (2) those using oxidizing agents other than molecular oxygen residue, consisting mainly of sodium peroxide and sodium to complete the oxidation. An example of the first class is carbonate, is dissolved in water and treated with acid. The the well-known Liebig method for ultimate analysis, in which carbon dioxide evolved is estimated by absorption in caustic the combustion is carried out in a stream of dry and pure solution. The method proposed in this paper consists of exploding oxygen, absorbing the carbon dioxide formed in potassium 2 For detailed directions see Bur. Mines, Tech. Paper 8. hydroxide solution. This method is the recognized stand-
A
Fuel Science Practice, 2 , 344 (1923). Z . Vcr. Rubenzuckerind., 46, 177 (lS96). “Fuel Gas Water and Lubricants,” p. 179, McGraw-Hill Book Co.. (1922). 8
Presented before the Division of Gas and Fuel Chemistry at the 73rd Meeting of the American Chemical Society, Richmond, Va , April 11 t o 16, 1927. I
1
September, 1927
I,VDUSTRIAL A X D ENGINEERING CHEMISTRY
the coal sample in a Mahler type of bomb, using approximately 20 atmospheres pressure of oxygen, and recording the temperature-time readings necessary for heating value computations. The gaseous products of combustion from the heating value determination are expanded into a mercurysealed gasometer and their volume is measured at about atmospheric pressure. Their carbon dioxide content is then estimated in the usual way and the total carbon of the sample computed. Apparatus
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with caustic solution are used to estimate the carbon dioxide content of the gaseous products.
Calibration of Gasometer Before starting the experimental work it was necessary to calibrate the gasometer. This was accomplished by introducing a measured amount of mercury into a gas-tight system through a separatory funnel. The system was connected t o the float chamber E so that a definite volume of dry air was forced into the gasometer. The system was brought to atmospheric pressure by raising or lowering the float chamber by means of an auxiliary screw attachment, and the calibration mark made on the float chamber. The calibration was continued in this way at 500-cc. intervals up to a volume of 6500 cc. Then, by means of a pair of dividers, the 500-cc. intervals were further divided into 100-cc. intervals. In the experimental work the gasometer was always read with the level sight, J , upon one of the calibration marks and the pressure, either positive or negative, relative to atmospheric was recorded on the water manometer.
GASOMETER-The mercury-sealed gasometer shown a t the left i n Figure 1 was constructed to use as small a n amount of mercury as possible by concentrically welding two h'o. 16 B. W. gage steel tubes, A and C, to a steel plate, D. The outside diameters of the steel tubes A and C are 10.16 and 8.25 cm. (4 and 31/a inches), respectively. A cover plate is welded to the top of the smaller tube, C, which is approximately 127 cm. (50 inches) long. The steel plate, D , is mounted on a wooden base 40 by Fuels Studied 61 cm. (16 by 24 inches) and 5 cm. (2 inches) thick, which in turn is mounted on castors. The float chamber, B , was constructed from No. 11 B. W. gage steel tube, by welding a cover plate to the For the purpose of checking the accuracy of this method top. A steel nipple connection, E , welded to the cover plate for total carbon determination, benzoic acid and sucrose observes as an inlet and outlet for the gases. The float chamber has an outside diameter of 95 cm. (33/4 inches), giving the tained from the Bureau of Standards, Washington, D. C., gasometer a capacity of approximately 9000 cc. It can be and five different coals obtained from A. C. Fieldner, of the raised or lowered freely in the annular space between the tubes Bureau of Mines, Pithburgh, Pa., were used for the experiA and C by means of the windlass, F,which is supported on the mental work. The coals, whose ultimate analysis had been wooden base of the apparatus. The length of the float chamber inch) shorter than tube c, giving determined at the Bureau of Mines, included semianthracite, is approximately 0 159 cm. ample room for the mercury t o flow in the annular space when the semibituminous, bituminous, and lignite. float chamber is lowered to its zero position. The mercury reservoir, G, was constructed from a sheet steel pan, approximately 24 cm. (9'/: inches) in diameter and 12.7 cm. (5 inches) high, by welding a right-angle connection t o the bottom. From 2 this connection a rubber tube leads to a steel nipple I ( connection, H , welded a t right angles to the outside tube, A . The reservoir is mounted on a wooden shelf which is supported from the base of the apparatus. A bowl-shaped collar, I,machined from cast iron J, and fitted t o the top of tube A , serves as a reservoir 'I t o prevent the loss of mercury by overflow in case the float chamber of the gasometer is rapidly forced t o its zero position. A level sight, J , attached to the collar to facilitate the reading of the instrument was constructed from a piece of sheet steel and extended nearly t o the wall of the float chamber. BOMB-The bomb, K, connected to the gasometer and manometer by means of the double needle valve, &I, and rubber tubing is shown in the upper righthand corner of Figure 1. The bomb, machined from monel metal, has a capacity of 255 cc. The needle valve (l), which closes the bomb during explosion, was carefully packed so t h a t the gases cannot escape around the connections when the valve is opened. This was accomplished by recessing the packing nut .and winding asbestos cord around the valve stem. A detailed drawing of the bomb6 is shown in the lower right-hand corner of Figure 1. The double needle valve, M , is connected t o the oxygen intake in the head of the bomb by means of .the brass nipple, N. The brass nipple (2) controlled by valve (3) is connected t o the float chamber of the gasometer at E by a heavy-walled rubber tube. A few centimeters from the nipple (2) a glass bulb, 0 , made from a 25-cc. volumetric pipet, is inserted in the line. The glass bulb is loosely packed with moist cotton gauze, wound on a copper wire and 'introduced into the bulb in a spiral manner so as to fill the free space completely. This serves to saturate the gases with water vapor as they expand from the bomb into the gasometer. The brass nipple (4)controlled by valve ( 5 ) is connected by a rubber tube to a three-way glass stopcock, P, which in 'turn is connected to the water manometer, L. A mercury-filled buret and a bubbling pipet filled
J
I
Copied from White's "Gas and Fuel Analysis," p. 2 6 0 , McGraw-Hill Book Co. (1920).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Experimental Work
T a b l e I-Total
Vol. 19, No. 9
Carbon and HeatincL Value of Coals ~
~~~~
TOTALCARBON HEATING VALWE A sample of fuel (0.8-1 gram) was exploded as usual in zj KINDOF COAL the bomb calorimeter containing approximately 20 atmosB. of M. Gasometer B. of h l . M o n ~ ~ ~ ~ t a ’ pheres pressure of oxygen to complete the combustion. The Cal. per Cal. per initial temperature of the water in the calorimeter was slightly Per cent Percent gram gram A.26840 Bituminous 73.4 below that of the room, so that the final temperature of the 73.4 system would be approximately equal to that of the room. 73.5 73.6 The temperature-time readings necessary for heating value 73.6 computations were recorded. The bomb was removed from Av. 73.5 73.5 7183 7193 the calorimeter can and connected to the gasometer through A.26847 Bituminous 76 2 the needle valve, M , by screwing the brass nipple, N , into the 76 4 7.5 5 head of the bomb. Then with both valves (3) and (4) open 76.0 and the stopcock P open to the air, the gaseous products Av. 76.1 76.03 7605 7595 from the previous run were expelled from the gasometer by A.26839 Semianthracite 63.6 lowering the float chamber to its zero point. When the float 62.9 chamber was in this position the level of the mercury came 62.6 62.7 just to the top of the steel nipple E in the float chamber, Av. 62.1 62.7 5861 5827 leaving the rubber tube and connections from the gasometer to the bomb filled with the gases from the previous run. The A26566 Semibituminous 83.2 83.1 volume of the rubber tube and connections was about 50 cc. 83.1 83.1 The carbon dioxide content of the gaseous products varied from 1 to 3 per cent with different runs, making it unnecesAv. 83.1 83.1 8083 8124 sary to consider the volume of the tube and connections in A.27336 Lignite 52.6 52.8 measuring the total volume, as it canceled out from one run 52.4 to another introducing a negligible error. 52.9 When the mercury in the gasometer and reservoir was a t Av. 52.4 52.67 4806 4811 the same level, valves (3) and ( 5 ) were closed. The needle valve (1)of the bomb was opened half a turn; then by using Table 11-Total C a r b o n of Organic Compounds valve (2) as a control, the gases were slowly expanded into COMPOUND THEORETICAL FOUND the gasometer. The float chamber was adjusted to the nearPer cent Per cent est calibration mark that would give approximately atmosBenzoic acid 68.7 pheric pressure. Then the water manometer was connected 68.9 68.8 to the system by closing the stopcock P to the air and open68.8 Av. 68.8 ing valve ( 5 ) . After waiting a few minutes until the pressure in the system had equalized, the manometer reading 42.2 Sucrose 42.3 was recorded and added to or substracted from the baro42.1 Av. 42.25 metric reading, according to whether the pressure in the system was above or below atmospheric. The room temperature and the gasometer reading were recorded. I n all the C o m p u t a t i o n of T o t a l C a r b o n f r o m Experimental D a t a experiments reported in this paper the gasometer reading The experimental data required for computing the total was 5000 cc. This value added to the volume of the bomb (255 cc.) represented the total volume of the gas under the carbon will be easily seen by taking as an example, the first run on the semianthracite coal, No. A. 26839, and making conditions of the experiment. the computation.
2%
Gas Analysis
Gas samples for analysis were withdrawn from the gasometer through stopcock P into a 100-cc. buret and the volume was measured over mercury. The carbon dioxide content was estimated by absorption in a bubbling pipet containing caustic solution. A couple of drops of acidulated water were introduced on top of the mercury in the buret to compensate for the dehydration of the gas in the caustic pipet. Four or five gas analyses were made on each explosion and the average value was taken to compute the percentage of total carbon in the fuel. I n computing the total carbon, 22,260 cc. were used as the gram-molecular volume of carbon dioxide under standard conditions of temperature and pressure. Results
Table I gives the results of determinations on the coals. The values reported in the last column are the average of two runs only, as the prime object of the experimental work was to check the method for total carbon determination. Corrections proposed by Geniesse and S00p7 for the solution of copper and nickel in monel metal bombs were applied in computing the heating values. Table I1 gives the results of determinations on the organic compounds. 7
THISJOURNAL, 17, 1197 (1925).
DATA Weight of coal sample Gasometer reading Volume of bomb Barometric pressure Manometer reading Room temperature Average C o t content of gaseous products
0.9860 gram 5000 cc. 255 cc. 747 mm. H g 173 mm. ofwater
+2 4 . O o C .
23.7 per cent
COMPUTATION = 5255 cc. Total gas volume = 747 12.84 = 759.84 Total pressure on system Absolute temperature of syst:? = 273 f 24 = 297’ K. 273 ,a9.84x 0.237 X 12 = 62.6percent Total carbon = 5265 X 297 X 760 986 22,260
+ - Correction
I n “Our Foreign Trade in Chemicals and Allied Products in 1926,” THISJOURNAL, 19, 469 (1927), the statement is made under “Acids and Anhydrides,” that “The largest export item is sulfuric acid, which goes entirely to Canada.” The reference should be t o our imports of su!furic acid and not our exports. Practically the whole of our large acid imports come from t h a t country, but acid exports are scattered among many countries, the sales to Canada being comparatively small, as that country is a large producer of sulfuric acid. The comparison is, of course, on the basis of quantity rather than value. OTTO WILSON
