US 2832673 A
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April 29, 1958 T. E. LARSON ET AL 2,832,673
APPARATUS AND METHOD FOR DETERMINING STEAM PURITY Filed July 29. 1955 5 Sheets-Sheet 1 J l T/zurszan 10760)? April 29, 1958 1'. LARSON ErAL 2,832,673
APPARATUS AND METHOD FOR DETERMINING STEAM PURITY Filed July 29, 1953 3 Sheets-Sheet 2 b AH: J A
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April 29, 1958 LARSON ETAL 2,832,673
APPARATUS AND METHOD FOR DETERMINING STEAM PURITY 3 Sheets-Sheet 3 7 7 6 6 A f 5 4. 5. 4 0 0/ A we, \W 3 & 3 /A 4 3 Z Z 3K 7 M m M6545 10 76543210 m 4 bX URQ @Q SQk 5 m J77 VE 772 UTE; Thar: f0 EL 4230/? flours Passe WA diva 5 9 E/ gy E 5 -tl'nited States Patent Q AP?ARATUS AND METHOD FOR DETERMINING STEAM PURITY Thurston E. Larson, Urbana, and Russell W. Lane, Champaign, Ill.
Application July 29, 1953, Serial No. 370,982
7 (Ilaims. (Cl. 23-230) This invention relates to a method and apparatus for determining the purity of steam or of steam condensate.
In the operation of modern steam boilers it is customary to treat the boiler feed water chemically or by means of ion exchanger material to soften the boiler feed water in order to eliminate, or reduce, the formah tion of scale in the boiler and to inhibit corrosion of the boiler metal. Such treatment of the boiler feed water often results in an increased tendency of the boiler Water to foam, and/or to become entrained in the steam leaving the boiler. This is particularly true in connection with modern steam boilers of large steam capacity and high rating. There is, therefore, a need for devices and methods for indicating and controlling the purity of the steam being generated, not only for the purpose of inhibiting or reducing corrosion of the metal of the boiler system but also for preventing the encrustation of superheater units and turbine blading, where turbines are used, since such encrustation results in decreased efliciency of the steam generating unit and also creates operating problems and an increase in the cost of maintenance.
It is, therefore, an important object of this invention to provide an improved method for the determination of the purity of steam, or of a steam condensate, whereby more accurate measurements may be made than were heretofore possible.
It is a further important object of this invention to provide a method and apparatus for determining the presence and quantity of inorganic contaminants, such as mineral salts from the boiler feed water, present in steam, or in a steam condensate.
It is a further important object of this invention to provide an improved method for the determination of the purity of steam, or a steam condensate, wherein the condensate is subjected to the action of ion exchanger material in order to remove cations resulting from the presence of ammonia or its derivatives, including amines, in the steam, or condensate, and thereby enable more accurate determination of the purity of the steam, or condensate, by hydrogen ion concentration or electrical conductivity measurements.
Other and further important objects of this invention will become apparent from the following description and appended claims.
On the drawings:
Figure 1 is a vertical sectional view of apparatus suitable for carrying out the method of our invention, for testing the purity of steam, with parts shown more or less schematically;
Figure 2 is a similar view to that of Figure 1 but of a modified form of our invention adapted for testing the purity of steam condensate, rather than steam;
Figures 3, 4 and 5 are charts showing typical determinations of the conductivity of steam condensate with and Without the removal of interfering ammonia or amines, the ordinates representing micromhos of con- M ductivity and the abscissae representing hours of time.
As shown on the drawings:
The method of our invention as applied to testing steam is best carried out in equipment such as that shown in Figure 1, in which the reference numeral 10 indicates generally an elongated tubular housing, formed of a number of sections 11a, 11b and of brass or stainless steel tube, the sections preferably being all of the same diameter and adapted to be coupled together. The elongated housing 10 is divided into an upper compartment 12 and intermediate and lower compartments 13 and 13a by means of an imperforate partition 14 between the upper and intermediate sections of tube, 11a and 11b. The partition 14 may suitably be clamped between collars 15 and 16 secured to the lower and upper ends, respectively, of the sections 11a and 1112.
A valved steam inlet pipe, or tube, 17 extends into the lower portion of the upper compartment 12 and is there provided with a few coils 18, or turns, terminating in an upwardly directed steam discharge nozzle 19. Another valved steam inlet 20 extends into the lower portion of the upper compartment 12 and downwardly through the partition 14 into the intermediate compartment 11b. The tube 20 is there provided with a few coils, or turns 21, from which, the tubing extends upwardly to form a steam discharge nozzle 22 that projects through the partition 14 and continues through the loop of the coils 18 to terminate at substantially the same level as the discharge nozzle 19.
The two nozzles 19 and 22, when the device 10 is in its intended position, extend parallel to each other and generally centrally of the tubular housing 11 for discharging their steam jets vertically upwardly. An impingement baflie 23 is mounted above the discharge ends of the nozzles 19 and 22 and in spaced relation thereto. Said impingement baffle 23 is suitably suspended from the wall of the tubular casing 11 so as to be slightly spaced therefrom, as at 24, to permit the upward flow of the discharged steam around the peripheral edge of said baflle. Above the baflle and within the upper compartment 12 is mounted a condenser 25, which may suitably take the form of cooling coils having an intake 26 for cooling water and an outlet 27 for the discharge of the water from the cooling coils. The condenser 25 is suitably suspended from a closure 28 attached to a collar 29, or the like, at the open upper end of the tubular section 11a. Said closure 28 is provided with a vent 30 for the release of any non-condensable gases separated from the steam, or the condensate formed therefrom.
As the steam condenses in the upper portion of the upper compartment 12, due to the presence there of the condenser 25, the condensate falls down by gravity and collects on the partition 14 to provide a pond 31 of condensate over said partition 14. An overflow pipe 32 having an open upper end 33 determines the height of the pond 31. Said overflow pipe 32 extends outwardly through the Wall of the tubular housing 11a and is in flow communication with a cell 34, which may be an electrode for measuring the conductivity of the condensate, or may be a pH electrode for measuring the hydrogen ion concentration of the condensate, or may be any other instrument or device for determining or measuring a characteristic of the condensate related to its purity. As illustrated, the unit 34 houses a pair of electrodes 35, from which Wires 36 lead to a recorder (not shown) for indieating and recording the conductivity of the condensate in the cell 34.
From the cell 34, a short length of tubing 37 leads the tested condensate to a vertical length of tubing 38, from near the upper end of which any excess may overflow to through a branch outlet 3d. The uppermost end of the tubing 38 is open to the atmosphere, as indicated at 40.
The vertical tubing 33 conducts the condensate from the upper compartment 12 into the lower closed end of the lower compartment 13a. A closure cap'41, similar to the cap 28, is provided at said lower end and is suitably secured to a collar 42 mounted thereon. A distributor plate 43 is positioned in the lower end of said compartment 13 in closely spaced relationship to the closure 41. Said distributor plate 43 serves not only forthe upward flow of the condensate into the compartment i351 thereabove, but also for supporting a bed 4-4 of ion exchange material. For this purpose, the distributor plate 43 is perforated, as indicated at 45.
The bed 44 is preferably formed of a cation exchange resin and is of suitable depth to insure substantially complete exchange of the cations in the condensate for hydrogen.
Above the resin bed 44 there is mounted a screen 46 that serves to prevent any particles from the resin bed from rising in the efiluent therefrom beyond the level of said screen into the intermediate compartment 13. The screen is suitably clamped between adjacent sections 11c and 11b of the tubular housing, as by means of a coupling 47.
An overflow pipe 48, having an open upper end 49 limits the level to which the effluent from the resin bed may flow. Such level is indicated by the dash line L, and the pond of eiiiuent therebelow is indicated by the letter F. It will be noted that the coils 21 are normally immersed in the pond P, and that these coils enclose the upturned end of the overflow pipe 48. A vent 56 is formed in the upper portion of the intermediate compartment 13 above the level L of the pond P. This vent is for the same purpose as the vent 30, namely to permit the escape of any non-condensable gases released by the boiling of the condensate, or by the heating thereof to substantially the boiling point.
The overflow pipe 48 is connected to a second cell, or unit, 51, which is similar to the unit 34, and which has wires 52 leading to a recorder (not shown). The contents of the unit 51' are allowed to overflow through a discharge connection 53.
While the conductivity method of determining the purity of steam, or of a steam condensate, has long been used, it
was soon discovered that the method was subject to grave errors due to the presence of carbon dioxide dissolved in the steam. The presence of the carbon dioxide gave a high reading on the conductivity indicator, which, in turn, would be translated into a higher than actual value for mineral contaminants. To eliminate this error, a degasifier unit was employed to efiect the release of carbon dioxide from the steam during the condensation thereof. In the apparatus just described, the steam coils 18 provide the heat necessary to drive off substantially all of the carbon dioxide that may be dissolved in the condensate, and the vent 30 permits the escape of such released carbon dioxide, or other'non-condensable gases. Thus, the present equipment also embodies a degasifier unit such as has been used previously in testing the purity of steam.
Even with such a degasifier unit, however, it was noted that in many boiler installations, large errors appear in the determination of steam quality. We have found that these errors are largely due to the presence of ammonia or of volatile amines, or amine salts, in the steam. Ammonia and the volatile amines exist in water as both the free gas and in the cationic form. The respective gas and ions are in equilibrium with each other and the partial pressure of the volatile gas is high when the pH is high and low when the pH of the water is low. The gas form of the ammonia and of the volatile amines can be substan tially separated from the water by boiling. The ionic form of the ammonia and of the volatile amines can be separated from the water by treating the water with a cationic exchange substance. As more of the ionic form is removed, the equilibrium eventually causes all of the gas formed to become ionic and the ionic form is then removed by the ion exchange substance. Thus, by use of both a degasifier and an ion exchange substance, virtually complete removal of the ammonia and volatile amines can be effected.
An important feature of the present invention is to provide a cation exchange bed which serves to remove the cations resulting from any ammonia or amines dissolved in the steam condensate. This apparently involves a replacement of the ammonium or the amine radicals by hydrogen ions, which combine with any free hydroxyl ions to form water. The water so formed does not of course have any effect upon the normal conductivity or hydrogen ion reading of pure water, and thus errors are avoided. The removal of the ammonium and amines, therefore eliminates their interference, previously noted with the sensitivity and accuracy of the method. At the same time, the ion exchange bed removes other cations, such as sodium, calcium and magnesium, which largely represent the mineral contaminants of the steam, which cations are replaced with hydrogen ions. The hydrogen ions increase the conductivity of the contaminated steam condensate and thereby make the device more sensitive to the specific presence of contaminating mineral matter. Consequently, even where there are no ammonium or basic amine cations present in the condensate, it is still advantageous to pass the condensate through hydrogen ion exchange material to replace any alkali metal or alkaline earth metal cations that may be present with hydrogen ions.
The upper portion of the device 10, including the elements in the compartment 12, provide means for continuously sampling steam, condensing the steam and maintaining the condensate at a constant temperature, which is conveniently substantially that of its boiling point. The steam venting rate as well as the fiow of steam is controlled to a point at which there is provided a satisfactory venting rate as well as condensing rate. While the upper portion of the equipment does not constitute a complete degassing condenser, it nevertheless does reduce the free carbon dioxide content to a low level. The purpose of maintaining the condensate at its boiling point is two-fold: first to remove the major proportion of carbon dioxide, and second, to maintain a constant temperature with relative ease in order that the results obtained by the measuring cells not be influenced by temperature changes. The measuring cells can equally well indicate the conductivity and/or hydrogen ion concentration if operated at any constant temperature, as for instance 25 C. Boiling does not, however, completely eliminate the content of dissolved ammonia and ammonia derivatives in the steam condensate.
By passing the partially degassed sample of steam condensate through an ion exchange column, such as the resin bed 44, to eliminate ammonia and its derivatives prior to the final conductivity measurement, we found that a response was obtained which was sensitive and unconfused by the presence of ammonia or of cyclic amines, and that the indication of conductivity would then have a direct relationship to carry-over of contaminants in the steam. With our device, and using our method, dissolved solids are converted to free mineral acidity, which has a known relationship with conductivity, and dissolved carbon dioxide can be removed by the subsequent re-boiling that is eifected in the lower compartment 13 by means of the steam heating coils 21, the non-condensable gases released as a result thereof being vented through the vent 50.
In the equipment above described, the upper compartment 12 constitutes the condensing compartment for steam introduced through the inlets 17 and 20 and discharged through the nozzles 19 and 22.
The apparatus illustrated in Figure 2 of the drawings is generally similar to that shown in Figure 1 but is specially adapted for use in testing condensed steam for condenser leakage. The tests may be conducted in either of two ways, one of which involves the use of the ion exchange bed without pre-boiling of the condensate, and the other of which provides for pre-boiling of the condensate to remove a major portion of the carbon dioxide before the ion exchange treatment to remove ammonia and/or amines. Re-boiling following the ion exchange treatment is provided in the lower unit to reduce the carbon dioxide contact to a minimum. A full description of the apparatus of Figure 2 follows:
Since the apparatus of Figure 2 is generally similar to the apparatus of Figure 1 and requires merely a relatively simple adaptation of the apparatus of Figure 1, many of the elements of both forms of apparatus are identical. Consequently, similar reference numerals will be used to indicate identical elements. In some instances, as in the case of the cooling coils 25 and impingement baflle 23, the particular elements are not necessary in the form of apparatus shown in Figure 2, yet serve a useful purpose when the apparatus is adapted for carrying out the previously described method.
Alternate condensate inlets A and B are provided in the apparatus illustrated in Figure 2. The alternate A condensate inlet is indicated generally by the reference numeral 60, while the alternate B condensate inlet is indicated by the reference numeral 61. The condensate inlet 60 feeds condensate into the lower part of the upper compartment 12 to provide a pool 31 of condensate up to the level determined by the upper open end 33 of the overflow pipe 32. The overflow pipe 32, as before, leads to a cell 34, which is in communication through an overflow tube 37 with a vertical length of tubing 38. A valve 62 is positioned in the line 38 below the overflow connection 37 from the cell 34, and another valve 63 is positioned in the alternate B condensate inlet 61, so as to enable the operator to use either alternate A or alternate B condensate inlets. When the alternate A condensate inlet 60 is used, valve 62 is open and valve 63 is closed, whereas when alternate B condensate inlet is used, valve 62 is closed and valve 63 is open.
In order to provide means for boiling the steam condensate in the pool 31, above the partition 14, a steam coil 64- is provided, which is fed through a steam inlet 65 controlled by a valve 66. The outlet from the coil 64 is through line 67 and valve 68 to a main steam outlet 69.
Similarly, means are provided for heating to boiling the condensate in the pond P above the resin bed 44 in the lower compartment 13a. Such heating means comprise a steam inlet 70 controlled by a valve 71 and leading to a coil 72, from which the steam is led through a pipe 73 that connects with the main steam outlet 69. As in Figure 1, the coil 64 encircles the overflow pipe 32, while the coil 72 encircles the overflow pipe 43, the open end 4? of which determines the height, or level, L, of the pond P.
If the alternate B method is used, condensate is admitted into the system through the inlet 61, with valve 63 open and with valve 62 closed. The condensate passes through the tubing 38 into the bottom of the device 16* and thence is distributed by the perforated plate 43 and passes under hydraulic head up through the resin bed as and through the perforated screen 46 until it forms a pond P up to the level L of the upper open end 49 of the overflow pipe 48. Valve 71 is opened as soon as the pond P is formed so as to heat the condensate in the pond up to its boiling point, or substantially so. The purpose of heating the condensate in the pond P is, of course, to reduce the carbon dioxide content of the condensate to a minimum.
The overflow through the open end 49 of the pipe 48 goes through the testing cell 51, where the conductivity of the condensate is measured. Alternatively, of course, some other property or characteristic directly related to the purity of the condensate could be determined in place of the conductivity, as for instance the hydrogen ion concentration by means of a pH indicator.
In the carrying out of the alternate A method, condensate is admitted into the inlet 60, while the valve 63 in the condensate inlet 61 is closed and the valve 62 is left open. Condensate is admitted into the lower portion of the upper compartment 12 until the pond 31 over the partition 14 rises to the height of the open end 33 of the overflow pipe 32. Prior to this happening, steam is admitted through the steam inlet 65 and the valve 66 to the coil 64 for discharge through the line 67 and valve 68 into the main steam outlet 69. Steam is similarly admitted through the inlet 70 and valve 71 into the coil '72 for discharge through the line 73 into the steam outlet 69.
In the upper compartment, the coil 64 serves to heat the condensate in the pond to substantially its boiling point and thus remove a major portion of the carbon dioxide before the ion exchange treatment in the resin bed After such pre-boiling of the condensate, the latter is conducted through the overflow pipe 32 through the unit 3% and thence into the vertical length of tubing 33 for passage upwardly through the resin bed 4-4. As before, the condensate, after passing through the resin bed, is brought substantially to its boiling point by means of the steam coils 72. In this case, the re-boiling in the pond P reduces the carbon dioxide content to a minimum.
it will be understood that the conductivity of the con densate in either the cell 34 or the cell 51, or in both, may be continuously recorded, or readings can be taken from time to time. Since the conductivity is directly rela ed to the concentration of electrolyte in the condensate, any conductivity reading can be converted into, or calibrated in, concentration by weight of an equivalent salt. if the ammonia and/or amine were not removed, an erroneously high conductivity reading would result, due to the fact that ammonium or basic amine radicals are present as ions. Their removal eliminates the falsely high reading that would otherwise occur. On the other hand, the hydrogen ions released in the ion exchange bed in exchange for inorganic ions (Ca, Mg and others) proportionately increase either the conductivity or the hydrogen ion concentration in the condensate overflowing to the test cell 51 and thus give an even more accurate determination of the mineral contaminant.
If the ammonia and/or amine is not removed, the conductivity reading may be considerably higher than it should be. The extent to which ammonia or amines interfere with the correct conductivity reading can be ascertained, whether the test is made on a freshly condensed steam or on an already formed steam condensate, by making simultaneous readings on the testing cells 34 and 51 and ascertaining the difference therebetween. Such simultaneous readings are shown in the charts in Figs. 3, 4 and 5.
in Fig. 3, the upper line represents the recorded conductivity without removal of ammonia interference, while the lower line 81 represents the recorded activity with ammonia interference removed. The peaks 82, 83 and 84 at the left end of the upper line 86 represent carry-over of mineral contaminants into the steam as does the peak at the left end of lower line 81. The high conductivity recorded by line Bil after hour 2 was due to the presence of ammonia and identified as such in a concentration of 0.95 p. p. m. (NH, ion) by analysis at cell 34 at hour 3%, whereas, there was no increase in conductivity at cell 51 after hour 2 and the ammonia content was determined by analysis at hour 3% as less than 0.1 p. p. in. (NH, ion).
In Fig. 4, the upper line 85 represents the recorded conductivity without the removal of amine interference while the lower line 86 represents the recorded conductivity with amine interference removed. With respect to the peaks 8?, 88 and 39 in line 85, these were found to include increases in conductivity due to 0.024 lb. of cyclchexylamine added at each of those respective times to the boiler.
In Fig. 5, the recordings were made at intervals represented by the sets of curves A, B and C, including upper and lower lines 91 91, 92, 93 and 94, 95, respectively. The peaks in the upper lines 90, 92 and 94- and in the lower lines 91, 93 and 95 both represent carry-over of mineral contaminants into the steam due to the sudden ncrease in steam withdrawal for such purposes as blowing a fire whistle, removing ashes or soot. The lower lines represent the recorded conductivity with ammonia interference removed and therefore are more indicative of the true carry-over experienced.
In a similar way, by the use of the form of apparatus shown in Fig. 2, leakage from condensers into the steam system can be detected in either of two ways, both of which involve the use of the ion exchange bed for the removal of ammonia or amine interference.
In the alternate B method, the condensate is admitted through the inlet line 61 only, passed through the ion exchange bed 44 and subsequently boiled in the pond P by passing steam through the coil 72. to reduce the carbon dioxide content to a minimum.
In the alternate A method, preboiling of the condensate in the pond 31 is eifected to remove a major portion of the carbon dioxide content in the upper compartment 12 before the ion exchange to remove ammonia and/or amines. Subsequent reboiling in the intermediate compartment 13 reduces the carbon dioxide content of the condensate to a minimum.
We claim as our invention:
1. Apparatus for determining the purity of water, steam and condensate likely to be contaminated with dissolved ammonia and its derivatives, which comprises an elongated casing having a partition dividing the same into upper and lower compartments, means for introducing steam into the upper compartment and discharging a jet thereof upwardly, a baffie against which such discharged jet of steam can impinge, cooling coils for condensing steam in said upper compartment for collection of the condensate on said partition, a bed of ion exchange material in said lower compartment, means for conducting condensate from said upper compartment to said lower compartment for passage through said bed, means between said bed and said partition for heating the effluent from said bed to substantially its boiling point, means for venting non-condensable gases eliminated during such heating, and means for determining a characteristic of the so treated condensate dependent upon the ionization of said condensate.
2. Apparatus for determining the purity of water, steam and condensate likely to be contaminated with dissolved ammonia and its derivatives, which comprises an elongated casing having a partition dividing the same into upper and lower compartments, means for introducing steam into the upper compartment and discharging a jet thereof upwardly, a bafile against which such discharged jet of steam can impinge, cooling coils for condensing steam in said upper compartment for collection of the condensate on said partition, 21 bed of ion exchange material in said lower compartment, means for conducting condensate from said upper compartment to said lower compartment for passage through said bed, means between said bed and said partition for heating the effluent from said bed to substantially its boiling point, means for venting non-condensable gases eliminated during such heating, and means for determining the conductivity of the so treated condensate.
3. Apparatus for determining the purity of water, steam and condensate likely to be contaminated with dissolved ammonia and its derivatives, which comprises an elongated casing having a partition dividing the same into upper and lower compartments, means for introducing steam into the upper compartment and discharging a jet thereof upwardly, a oafile against which such discharged jet of steam can impinge, cooling coils for condensing steam in said upper compartment for collection of the condensate on said partition, the steam introducing means including coils above said partition for heating the there on collected condensate to the boiling point, a vent for non-condensable gases released from said condensate a bed of ion exchange material in said lower compartment, means including an overflow positioned above said partition for conducting condensate from said upper compartment to said lower compartment for passage through said bed, means betwen said bed and said partition for heating the efiluent from said bed to substantially its boiling point. means for venting non-condensable gases eliminated during the last recited heating, and means for determining a characteristic of the so treated condensate dependent upon the ionization of said condensate.
4. In a method of determining the purity of steam in which a steam sample is condensed and held at the boiling point to eliminate carbon dioxide and subsequently subjected to a test depending upon the ionization of the sample to determine the solids content of said sample, the improvement which comprises subjecting said sample prior to said test to ion exchange sufiicient to remove cations derived from ammonia and amines.
5. In a method of determining the purity of steam in which a steam sample is condensed and held at the boiling point to eliminate carbon dioxide and subsequently subjected to a test dependent upon the ionization of the sample to determine the solids content of said sample, the improvement which comprises subjecting'said sample to ion exchange with a cation exchange resin capable of exchanging hydrogen ions for cations derived from ammonia and amines.
6. The method of determining steam purity of a steam having a sufi'icient concentration of ammonium ions to give an erroneous solids concentration determination when subjected to an electrical conductivity test which comprises condensing a sample of the steam, maintaining the resulting condensate at substantially its boiling point to eliminate carbon dioxide, passing the condensate through a bed of cation exchange material capable of exchanging hydrogen ions for said ammonium ions to remove substantially all of said ammonium ions, and thereafter subjecting the ammonium ion free sample to an electrical conductivity measurement.
7. In the method of determining the purity of a condensate of steam in a steam generating and condensing system wherein said condensate in said system has cations derived from the group consisting of ammonia and amines and alkali metal and alkaline earth metal compounds, said cations derived from ammonia and amines being in a concentration suflicient to give an erroneous solids concentration determination when subjected to an electrical conductivity test, the steps which comprise subjecting a sample of condensate of said steam to cation exchange material capable of exchanging hydrogen ions for cations derived from said group to remove substantially all of said cations from said sample and thereafter subjecting the resulting sample to an electrical conductivity measurement.
References Cited in the file of this patent UNITED STATES PATENTS 2,046,583 Rummel July 7, 1936 2,372,233 Thurston Mar. 27, 1945 2,422,054 Tiger -1 June 10, 1947 2,549,388 Rivers Apr. 17, 1951 2,617,766 Emmett Nov. 11, 1952 2,628,194 Gilwood Feb. 10, 1953 FOREIGN PATENTS 531,418 Great Britain Ian. 3, 1941 495,101 Belgium Apr. 29, 1950 OTHER REFERENCES Analytical Chemistry, vol. 3 (1931), pages 317 to 320, article by Rummel; vol. 22 (1950), pages 64 and 1' 65 of article by Kunin.