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is found, upon inspection, to have missed the principle of free phenol liberation in cursu. This, no doubt, came about through the use of additional reactants, such as calcium carbonate and the like; at least, the preliminary step of acidification is described as necessary to set free the phenol. I n our experiments connected with the use of salts of strong bases and weak acids, we make no addition of acid to reaction product for the purpose of liberating phenol; the phenol is already there in the free state. This new type of phenol manufacture, with copper as a catalyst, requires not so high a temperature as by use of caustic soda on the same halides. The introduction, therefore, of the benzene halide-sodium carbonate mixture into a continuous system offers a great improvement over the former processes. Above all is this to be approved by reason of the fact that sodium carbonate solution contributes in far less degree than caustic soda to the production of hydrogen in closed metallic systems. Organic chemical reactions under high pressure are now in the first stage of development. The difficulties that have attended the employment of hot caustic liquors within metal tubes have demanded our constant attention. Already a marked improvement in the continuous system, as heretofore described, is before us. The invention, as such, is made the subject of patent application by the senior author now pending. It consists primarily in the employment of a set of tubes for intake of the caustic on the one hand, and a set for the intake of organic compounds on the other. Each tubular system will be constructed of properly selected material. Thus, the caustic soda solution will preferably be supplied through heated copper tubes; the benzene derivatives will be supplied cold and through any sort of tubing. The two reactants will be pumped into copper or copperlined autoclaves, either in individual or continuous set-up, and the heat supply in the caustic will be made to suffice for the completion of the hydrolysis of organic derivatives. Following this stage, either by cooling directly or pumping through an additional continuous system, discharge will
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be made and the h a 1 liquor worked up for hydroxy aromatic compounds. I n the procedure just outlined it will be noted that little if any overheating of organic derivatives is possible. Rapid and complete hydrolysis will be highly favored from the start. The time of actual reaction will be reduced to a minimum, possibly from 3 to 5 minutes for a benzene halidecaustic soda mixture. In the midst of experimental work with constant attention upon results carried out over monthly periods, it is yet too soon to state that our process is just so and so. That is exactly what it is not. As to the relative merits of the new process as compared with the old sulfonation process, this is a matter of individual opinion. Whatever the disparagement in prices between chlorine and sulfuric acid as intermediary reactants, this is of no concern to chlorine manufacturers; and as for labor, the sulfonation process really requires an abundance-the new process runs almost by itself. Acknowledgment
Many of the experimental data presented in this paper have been taken from the reports made to The Dow Chemical Company by William H. Williams and Joseph W. Britton. The authors hereby acknowledge their indebtedness to these industrious members of our Organic Research Division. We wish further to express to Thomas Griswold and the Engineering Department, and to Mark E. Putman of the Production Department, our highest appreciation for the keen interest and assistance they have always rendered in the unraveling of complexities that were wont to confront us. And, to the long line of investigators who have striven to establish the practicability of benzene halide hydrolysis, we would express our admiration of their each and every effort. Finally, it can be written that their efforts and ours have produced a new successfully operating synthetic phenol plant that will afford the arts and industries a chemically pure phenol at lowest prices.
Measurement of Surface Temperature’ D. F. Othmer and H. B. Goats DEPARTMENT O F CHEMICAL EKGIKEERIXG, UNIVERSITY
HE study of the rate of heat transfer is no longer merely one of over-all coefficients-from the heating to the cooling medium-but has become instead the study of individual film coefficients. The concept of at least a single stagnant film on each side of a metal wall dividing the two fluids a t different temperatures is generally accepted. These films may be considered to transfer heat entirely by conduction and, because of the low thermal conductivity of the fluids, divide between them almost the entire difference between the temperatures in the bodies of the two fluids. The high thermal conductivity of the metals used in tubes as compared with that of any fluid film makes the temperature drop across the tube almost negligible for work with any degree of accuracy yet attained. For example, in the case of steam condensing on one side of a tube to heat a liquid on the other, the tube may usually be considered radially isothermal. An accurate measurement of this tube temperature is essential for calculating the film coefficients. Since the temperatures of the two fluids and the amount of
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Received December 16, 1926; revised paper received November 5,
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heat passed through the tube wall can usually be obtained very simply, the only difficult measurement is that of the tube temperature. Lack of general agreement between investigators with regard to film coefficients is probably due t o faulty tube-temperature measurement. Previous Work
An accurate means of measuring tube temperatures was desired by one of the authors as a first requisite in the study of the rate of condensation of steam. A number of methods have been published, which will be briefly reviewed for comparison. This is not a complete bibliography; in fact, some of the methods found were so obviously crude or inaccurate as to deserve no consideration. A case in point is the use of plugs of easily fusible alloys sunk in the metal. The metal temperature was taken at the end of an experiment as the mean between the known fusion temperature of the last plug to fuse and that of the one with the next higher melting point which did not fuse.2 MERCURY THERMOMETERS-The use of mercury thermom2
Durston. Trans. Insl. Naml Arcb., 1898, 130.
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For determining the therconductivity of iron , Methods for attaching thermocouples to heating Hall" copper-plated the top surfaces by mechanical means may give satisfactory and bottom Of a cy1inder Of results, but may also give very erratic results. If the the metal t o a thickness of junction is formed by plating a layer of the second about2mm' "PIJer wires metal on the surface whose temperature is to be were attached to the top Or studied, and if the leads are attached before plating and bottom surfaces, which perature' The direct so that they are imbedded in the plate, uniform results were maintained a t different urement Of the linear exare obtained. Directions are given for making nickeltemperatures with hot and pansion Of a tube as a copper junctions on tubes. cold water. The thirteen of estimating its temperadifferent thermocoudes so ture was used bv S t a n t ~ n . ~ formed varied among themHis extensometer could be read to 0.1" F., but he found it necessary to calibrate it be- seIves by an amount equaI t o 8 to 10 per cent of the total fore and after every experiment because of uncertainty of the temperature drop from top to bottom of the iron. metallic expansion. The extensometer method was also used The methods of attaching thermojunctions experimented by Soenneckens with a more elaborate apparatus, which he also with in this laboratory include (1) soldering wires to surface found was accurate only if frequently recalibrated. This of tube; (2) soldering wires together and then to walls of a method, like the two previous ones, is obviously to be used small hole in the tube; (3) soldering wires in separate holes only with experimental apparatus especially designed with in tube; (4) swaging wires in small holes; (5) butt-welding reference to the method of temperature measurement, and wires and soldering the junction in a slot in the tube; (6) soldering or welding wires to a butt junction, insulating all as such has only a very limited application. Sucksmiths indicates a large refinement on any previous but this junction with fine asbestos fiber and soldering this The insulation work with an extensometer, although he did not measure junction in a hacksaw slot in the tube tube temperatures. He applied the ultramicrometer to the of method (6) was covered with solder and the whole surface measurement of small increments of temperature. (as also the previous ones) was filed smooth. The tubes on THERMOCOUPLES-Thermocouples have been the most which these wires were fastened were mounted so that steam common means of measuring tube temperature because of condensed on the outside and cooling water circulated on their applicability to distant reading. It is always possible the inside with the wires drawn out of the steam space through to devise a method of running wires to the junctions, but a packing gland. Concordant results could not be obtained this entails a complication which must be overcome before even among several couples put on in the same manner, and the use of thermocouples can even be considered. The leads all methods but (6)12 gave a temperature drop much higher to the junction on the tube, after leaving the tube surface, than was expected. The error in the readings was due to must traverse a zone of higher or lower temperature than localized heating of the tube by heat conducted along the that of the tube itself. This results in a conduelion of heat thermocouple wire from the steam. Discrepancies between along the wires, which in turn causes an increase or decrease several couples put on by method (6) were not so large, but in temperature a t the junction of the wire with the tube wall. amounted to differences of from 5 to 15 per cent of the total That this causes a very serious error has been shown by several temperature drop from steam to tube. previous experimenters and by some trials in this laboratory, Electrodeposition Method in which the thermocouples formed by simply sealing the two wires in the tube wall indicated a temperature closer to that The method finally adopted depended on the embedding of the steam than the known temperature of the tube found of wires in an electrodeposited layer of the same metal on by another method. the surface of a tube of a second metal. I n effect this proSeveral experimenters have minimized this difficulty by vided a comparatively broad interface-i. e., a part of the shielding the small section of tube where the thermojunction
ably find it capable of producing very good results. EXTE'SoMETER-The exp a n s i o n Of a body with change of temperature is the p r o p e r t y usually used to
4
6
a
64, 481 (1897). Trans. Roy. SOL.(London), A190, 67 (1897). Milt. Forschungsarbcitcn, 108-109, 33-78 (1911). Phil. Mag., [e] 43, 223 (1922); see Whiddington, Ibid.,
(1920).
Proc. Insl. Mech. Eng. (London), 1909, 1317. Trans. Insl. Eng. Shipbudders Scotland, 1713, 57. 8 J . Sci. Inslrurnenls, 2, 260 (1925). 10 I n d . Eng. Chem., 18, 728 (1926). 1 1 A m . A c a d . A r t s Sci., 34, 283 (1898). 12 Devised and utilized by L. A. Phillips in this laboratory. 7
* Engineering,
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[e] 40, 634
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surface of the tube-for one junction of the thermocouple. A second wire of the same metal as the tube was either similarly embedded in an electrodeposited plate of its metal on another section of the tube or pressed against an unplated spot on the tube. The cold junction was made in the usual manner, and the wires were connected to selective switches and thence to a potentiometer. Metals Used
Since only pure elementary metals can be used in this type of thermocouple, the first to suggest themselves are copper and nickel. For example, a copper tube may have nickel wires embedded in a nickel deposit plated on its surface for one side of the circuit and a copper wire pressed or copperplated to an unnickeled spot for the other side. The nickel wires are then welded or soldered to copper wires leading to the potentiometer and these junctions kept in an appropriate ice bath. A metal which would remain unoxidized and constant in regard to surface conditions affecting the rate of heat transfer was necessary and nickel fulfils that requirement better than copper. Note-Badger, “Heat Transfer and Evaporation,” p. 134, Chemical Catalog Company, 1926, shows that copper is liable to oxidation, which renders consistent experimental results unobtainable Later work in his laboratory, as yet unpublished, shows that after a time the surface conditions of copper tubes are unchanged with respect to the rate of heat transfer.
Thickness of Layer
It was at first considered necessary to plate a very thick layer of nickel on the copper tube, and the initial experiments were made with a plating as thick as 2.5 111111. (0.1 inch). Later experiments showed that a layer one-fifth to onetenth as thick was satisfactory, but even a layer of this thickness is quite difficult to put on smoothly. A much easier operation is the enclosure of copper wires in an electrolytic deposit of copper on the surface of a nickel tube, because a thick copper plate may be obtained without roughness. The plated deposit must be thick, preferably as thick as the diameter of the wires, in order that the heat conducted along the wires may be dissipated through a large mass of metal before the interface is reached, to prevent irregularities of temperature there. A thick layer introduces an error, however, because the temperature is measured, not on the outer surface of the tube in contact with the fluid, but a t the interface between the plating and the tube proper. I n accurate work correction may be made for this by means of the equation Q = X S AO/At, where Q, the quantity of heat flowing; X, the coefficient of thermal conductivity of the metal in the plate; S, the area; and At, the thickness of the electroplate, are all known and the temperature correction, Ae, is to be calculated. Preparation of Tube
.
The preparation of the tube for plating begins with a thorough cleaning with fine emery paper, wet pumice stone and a brush, hydrochloric acid, 10 per cent caustic solution, hydrochloric acid, and distilled water. The alkaline-acid ilm of water on treatments are repeated until a continuous f the surface does not “break.” After the mechanical and before the chemical treatment, the nickel wires for the thermocouple leads are attached. A piece of No. 30 nickel wire about 20 cm. (8 inches) longer than the circumference of the tube has the end bent back sharply to form a hook (Figure 1). The wire is wound once around the tube loosely and caught in the hook turned on the end. .It is then caught with a pair of pliers at a point opposite the hook and a loop twisted until the wire holds tightly. The free end of the
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wire, to which the lead wires will later be soldered or welded, is either given several coats of a rubber-base cement or, better, is entirely covered to its junction with the tube with a piece of small rubber tubing closed with cement. This is to prevent enlargement of the wires due to plating and must be carefully done because the solution plates through many ordinary insulations. Plating Two methods of plating were used-the first for 2.2-cm. (‘/*-inch) tubes and the second for 7.6-cm. (3-inch) tubes. An anode was rolled out of sheet nickel to form B hollow cylinder about 7 cm. larger in diameter than the smaller tubes and a trifle longer than the part of the tube it was desired to plate. The tube was mounted concentrically with the anode in the plating solution. This method is applicable only for small tubes or for one on which only a small band is to be plated, because of the large anodes which would otherwise have to be employed. For the 7.6-cm. tube it was simpler t o suspend it from a bearing and rotate it in the solution a t about 100 r. p. m., in which was also immersed a standard rolled bar anode. The ends of the tube were closed with wooden plugs axially drilled for an iron rod which fitted tightly through them. A single heavy copper wire from the top of the tube to the vertical shaft served both as a flexible coupling and conductor of the plating current. The tube was filled with water to prevent its floating in the solution and was rotated smoothly by the motor FIGURE I driving the vertical shaft. The plating tank for B band more than 60 cm. (2 feet) long is most simply made by cementing together sections of standard sewer tiling. The nickel-plating solution used was made up of 2.25 N nickel sulfate, 0.30 N boric acid, and 0.1 N nickel chloride. To this was added sufficient nickel carbonate to form a slight sludge, which was filtered off after boiling. The pH of the boiled solution was adjusted to 4.3 to 4.7 with sulfuric acid, and maintained in that range during the plating process by adding more sulfuric acid or nickel carbonate. One cubic centimeter of hydrogen peroxide was added per liter of solution per hour of plating time to prevent bubbles. A fixed brush held against a rotating tube or a periodic brushing of a stationary tube was found to keep the surface free from bubbles, but was not used except experimentally because of the mechanical difficulty presented by the attached wires. The solution was heated to about 40” C. before plating started, and the heat of reaction kept it a t approximately that temperature throughout the process. If the solution cooled, a part was removed, heated, and returned. For the first tubes the current density was held at about 450 to 550 amperes per square meter of surface by a controlling rheostat, but in the case of the 7.6-cm. tube, which was to be plated for 1meter of its length, the capacity of the generator limited the density to about a third of this value. When the plating was put on as thick as was possible without obtaining bubbles or excessive “tree” growths, the tube was removed from the solution and all “buds” filed off. The irregularities built up around the wires and their hooks and loops were filed until the whole tube had a smooth surface. Description of Tubes and Temperature Measurements
0
Of the tubes which were prepared with thermocouples in this way, three will be described. TUBE1-The first (Figure 2) was a 2.2-cm. (’/&inch) copper tube plated in a 28ter graduate using a sheet-nickel
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INDUSTRIAL AND ENGINEERING CHEMISTRY
anode. It was rotated, and in 20 cm. of length near one end had nine wires embedded in a nickel plate about 2.5 mm. thick. Except for the 20 cm. to be plated, the tube was protected from electrodeposition by rubber tubing tied on tightly. After plating, the tube was placed in a lathe and a cut in the plating made between the third and fourth and between the sixth and seventh wires (Figure 2). This left three thermocouple wires on each of the three nickel bands. The ends of these wires were soldered to nickel wires leading to copper junctions which were immersed in melting ice. A single return for the other side of the circuit was made by winding a bright copper wire around the polished end of the copper tube and connecting this wire to the measuring instrument. In this, as in all other experiments, the thermocouple wires were insulated with small rubber tubing. The tube was then steam-jacketed (the copper lead wire was connected outside of the steam jacket) and a connection made
FIGURE 2
to circulate cold water through it. Since it was possible to measure the inlet and outlet temperatures and the volume of this cooling water, a complete heat balance could be made. Note-If the wires are t o be exposed to steam for long periods of time, the sulfur in vulcanized rubber destroys them. Envulcanized rubber tubing or varnished cotton tubing as is used in radio work may be used if the wires are otherwise uninsulated. Copper wires which are enameled and protected by double silk insulation have been uninjured when encased in vulcanized rubber tubing in steam for a per.od of several months.
Several average series of readings are reproduced with a temperature drop of 3 to 5 degrees from the steam to the tube -4larger temperature drop could not be obtained with this apparatus, but more heat was flowing per unit area than in the usual evaporator or condenser. 2.170 millivolts correspond to 100” C., and the millivolts corresponding to the temperature of the tube surface are shown for each thermocouple. (1) 2.165 2.099 2.106 2.121 2.074
(Figures in millivolts) (2) (3) (4) (5) (6) (7) 2.160 2.160 2.164 2.164 2.164 2.164 2.096 2.092 2.100 2.100 2.100 2.100 2.100 2.100 2.111 2.109 2.105 2.100 2.121 2.120 2.120 2 118 2.118 2.118
(8)
2.162 2.100 2.100 2.124 2.093 2.093 2.093 2.093 2.093 2.093 2 093
(9) 2.161 2.100 2.100
2.124 2.093
Each line of data represents conditions maintained as nearly constant as possible with this rough apparatus. In some cases the steam-film coefficient was calculated and the average of the values obtained was 3100 b. t. 11. per square foot per degree Fahrenheit per hour, which is in good agreement with the work of other experimenters using other methods of temperature measure. TUBE2-The second tube (Figure 3) was 7.6 em, (3 inches) outside diameter and was rotated while being plated as described above. Six wires were equidistantly spaced in the middle 75 em. of its 125 em. length. Except for about 12 em. on each end, the tube was covered with a firm, smooth nickel layer approximately 0.25 mm. thick. The exact value mas obtained from the difference of the averages of about 120 micrometer measurements before and the same number after plating. A thicker plate might have been better, but it was realized from the appearance of the tube that a rough surface would be obtained if the plating was continued. Experimentation in this field would probably make it possible to produce much thicker layers of electrodeposited nickel than have so far been obtained without surface roughness.
127
A channel about 6 mm. (I/d inch) in width and deep enough to expose the copper was cut entirely around the tube about 15 cm. from each end. This localized the central part of the tube ( A , Figure 3) as the thermocouple surface, and eliminated temperature discrepancies due to end conduction. The single copper lead ( B )to the potentiometer was attached to a copper screw so arranged that it could be screwed down tightly on the bare end of the copper tube. I n addition to the nickel wires leading to copper wires in cold junctions, a copper wire was soldered to each nickel wire a t a point (C) about 10 em. from the attachment with the tube. Thus each of the six thermocouple circuits had three junctionsthe junction on the tube surface, the junction about 10 cm. from the tube in the steam space, and the cold or ice junction. By combining any two of these three junctions in pairs it was possible to obtain three different temperature differences: that between the tube and the ice point-i. e., the temperature of the tube above 0” C.; that between the steam and the ice point-i. e., the temperature of the steam above 0 ” C.; and that between the steam and the tube-i. e., the “temperature drop” directly. Since this last temperature difference is small compared with the actual temperatures of the tube or the steam, and since in any apparatus for the study of heat transfer fluctuations of operating conditions, and hence temperature, are unavoidable, it is an advantage to be able to read the small temperature difference directly instead of finding it by subtraction of the tube temperature from that of the steam. This method eliminates the simultaneous readings of tube and steam temperatures which would otherwise be necessary. The thermocouple wires were insulated and connected to a selective switchboard, which was in turn connected to a Leeds and Northrup type K potentiometer. The tube was fixed in its position in an apparatus for studying the rate of condensation of steam which will be described in another report. The thermocouples were calibrated and, except for one which had been damaged, were so consistent in their readings that they were connected in multiple and always read that way. Since a reading of e. m. f. on a potentiometer is independent of the resistance of the circuit, no corrections for the decreased resistance of the several thermocouple circuits in parallel, as compared with that of a single one, were h
SELECTIVE SWITCHBOARD I
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necessary. This difference of resistance might cause an appreciable error if a low-resistance millivoltmeter were used to measure the thermal e. m. f. TUBE3-The third tube, which was plated, was a 2.2-em. (‘/pinch) nickel tube 125 em. long taken from a Swenson experimental evaporator. Four copper bands about 2 em. wide and 1 mm. thick were electrodeposited a t different distances along the length. Two No. 30 copper wires were embedded in each of two of the bands, and a single KO.30 copper wire was embedded in each of the other tlvo. Rubber tubing prevented plating of the tube except on these bands.
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A glass graduate was used as a plating tank, a cylindrical anode was used and the tube was not rotated. The solution was 1.6 N copper sulfate and 1.6 N sulfuric acid, and the deposit was thicker and smoother than the nickel deposits. Near one end of the tube a band of nickel enclosing two nickel wires was plated on, the wires forming the other side of the thermocouple circuit. After the usual external connections were made with the tube in position in the evaporator, the thermocouples were calibrated against a standard thermocouple. Water was circulated in the evaporator a t various temperatures and the thermocouples checked among themselves t,o 0.03-0.05° C. Discussion of Results
The agreement among the thermocouples attached to these three tubes was of the same order when there was a large temperature difference between the tube and the steam as it was when the tube and surroundings were in thermal equilibrium. Temperature differences of as high as 35" C. between tube and steam have been measured with these thermocouples, and the agreement between readings has always been within a millionth of a volt, corresponding to about 0.05" C., when it was possible to maintain uniform operating conditions during the reading of the thermocouples. As has been mentioned above, a thicker and smoother electroplate could be deposited if the surface of the tube was
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brushed during plating. A very thick plate of nickel (3 to 4 mm.) can be put on in this way in a hot solution with high current density if no wires are to be embedded. An arrangement of a nickel screw to be pressed or screwed against a point of the nickel surface could be devised which should answer the same purpose as the embedded wires. No experiments have been made with this type of junction, or with a junction formed by simply welding a nickel wire to a heavy nickel plate. Because of the very high rate of heat transfer between a condensing vapor and a metal surface, the measurement of the temperature of a surface on which steam is condensing is more liable to errors than a similar temperature measure ment of a surface through which heat is passing between two fluids without a change of state. It is therefore believed that this method, which has been successful in several studies in the condensation of steam during the last year, would be even more accurate in determining the temperatures of other surfaces through which heat was flowing-as, for example, in boilers or heat interchangers. Acknowledgment
The authors wish to express their thanks to Prof. W. L. Badger of this department for his helpful supervision of the work, and to Prof. E. M. Baker for his assistance in the plating processes.
Our Export and Import Trade in Chemicals' A Five-Year Review Frank Talbot and W. N. Watson WASHINGTON, D. C.
UBLIC attention is at present focused on the recent international agreements among the cartels or consolidations in Europe, for the purpose of fixing prices, preventing overproduction, and for the division and expansion of export markets, the last possibly a t the expense of the future export trade in chemicals from the United States. An analysis of our domestic import ahd export trade in chemical products is therefore of timely interest and will serve as a basis for future comparisons. The prospect of a tariff revision in the United States emphasizes the desirability of a careful study of the effect of the Tariff Act of 1922 on our import trade in chemicals during the past five-year period. A revision of the tariff involves a readjustment of tariff rates, a reclassification of many products, and the transfer of some items from the free list to the dutiable list, and vice versa. In a study of competitive conditions by the Congress, one of the principal criteria for gaging competition is the imports of any given commodity. A review of our import and export trade, furthermore, reveals many significant changes resulting from the development of new chemical products which either serve as substitutes for some of those now in use or have found new and distinct uses. I n order to have a common basis for comparison, values must be taken rather than quantities, and a correction in value made according to changes in the index of commodity prices. Index numbers for chemical products, as published by the United States Bureau of Labor Statistics, are shown in Table I. The price base used in this table is 1926, as it
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Received December 13, 1927.
has become increasingly apparent that the year 1913 is now too remote to furnish a satisfactory base for comparing price levels in recent years. Table I-Chemicals a n d Allied Products: Index N u m b e r s of Wholesale Prices, b y Groups of C o m m o d i t i e s , 1914, 1922-1926 (Source: 1923-1926,Bureau of Labor Statistics; 1914, 1922,by calculation)
1914 1922 Chemicals and drugs: Chemicals Drugs and pharmaceuticals Fertilizer materials Mixed fertilizers All chemicals and drugs Paint materials
1923
1924
1925
1926
85.1 95.6 100.6 102.2 104.1 100.0 58.3 87.4 95.7 83.7 102.7 102.5 107.4 77:7 9$:9 101.1 . . . . . . 101.3
95.8 97.7 100.0 92.6 98.8 100.0 95.9 100.4 100.0 98.9 101.8 100.0 99.7 109.3 100.0
The index number of the wholesale prices of all commodities on the same base is as follows: 1914 1922 1923
64.0 97.3 100.6
1924 1925 1926
98.1 103.5 100.0
I n the present article the statistics in general have been tabulated in accordance with the classification used by the Department of Commerce in "Foreign Commerce and Navigation of the United States," in 1926. As the classification in that publication has changed somewhat from year to year, it has been necessary to retabulate the data for each of the years prior to 1926 in order to give a uniform basis of comparison. Chemicals and related products have been classified in three groups, as follows: Group A consists of coal-tar chemicals, medicinals, pharmaceutical preparations, and industrial chemicals. Group B includes allied products, such LLS paints,
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