Hydrogen-Ion Concentration as a Basis of Refinery Alkalinity Control

Investigation has shown that buffer substances cause large errors in titrating alkalinities of sugar refinery products, and therefore refinery alkalin...
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December, 1925

INDUSTRIAL A N D ENGINEERING CHEMISTRY

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Hydrogen-Ion Concentration as a Basis of Refinery Alkalinity Control' By A. A. Blowski and A. L. Holven CALIFORNIA& HAWAIIANSUGAR REFINING CORP., CROCKBTT,CALIF.

Investigation has shown that buffer substances cause gation of the development of HEsubject of alkalinity large errors in titrating alkalinities of sugar refinery acidity in refinery products has always been recproducts, and therefore refinery alkalinity control must and finally to the complete ognized as one of exbe based on hydrogen-ion determinations. There has development of a roundedtreme importance in the sugar been developed an original form of color chart, consistout system of control. industry. Particularly is this ing of carefully dyed celluloid sheets representing the true in cane-sugar refining, Relation between Titrated colors of methyl red, bromothymol blue, and phenolbecause only a very narrow Alkalinity, as Determined 4.5 and 10, which greatly simpliphthalein between pH with Common Indicators, range of alkalinity is perand True Alkalinity fies "spot test" determinations of hydrogen-ion conmissible on account of the centration as a means of practical control. To minidanger involved in operating The large number of remize both sucrose inversion and glucose decomposition, with either excessive alkafinery products that are regproducts are maintained close to pH 7 by neutralizing linity or excessive acidity. ularly tested for alkalinity the acidity in the entering products and also that deAs is generally known, if vary greatly in their nature, veloped at later stages of the refining process, using 2' cane-sugar products are limed and as the nomenclature difBrix lime. This control has resulted in more uniformly to excessive alkalinity, invert fers somewhat a t the differneutral conditions with only half the previous amount sugar is decomposed, with ent refineries, the names and of lime introduced to process, thereby substantially the formation of objectionnature of the products enterreducing the molasses production resulting from able coloring matters and of ing into this discussion have melassigenic lime salts. organic acids, with the result been tabulated in Table I. that not only mag the original Table I-Description of Refinery Products acidity of the material barestored , but melassegenic lime salts Approx. Approx. apparent Stammer are left in process, thus diminishing the yield of crystallizable purity color sugar. On the other hand, if these products are insufficiently PRODUCT coefficient Der 100' Brix NATURB OF PRODUCT MiscelEaneok Basic Products limed the normal acidity of the material will cause considerDark viscous sirups obable inversion of sucrose with resulting loss of extraction. tained from washing of Affination sirup (green and wash) 80 t o 8 3 600 raw sugar and containHowever, in spite of the importance of close regulation, ing bulk of impurities of I raw sugar the customary alkalinity control in cane-sugar refineries has Raw liquor 99 20 Solution of washed raw been, until recently, quite simple and crude. The common sugar I Sweetwater from char filpractice has generally been to add heavy-density lime, by 3oo ters, cloth filters, and bag laundry, concenmeans of buckets or similar devices, to one or two products Concentrated sweet water 80 trated t o 60' Brix only-generally those to be cloth-filtered-controlling the 2oo Lowest grade of remelt sugar, which is passed alkalinity by phenolphthalein titrations or litmus paper tests. No. 3 remelt sugar 77 through whole refining system again with other Other products, in passing through the house, were generally low-grade material unlimed, though in most refineries some record was kept of Products Entering and Leaving Char Pilfers 6oo { Affination siru-luted, alkalinity or acidity of these products to one of these indi- Clear affination sirup 80 limed, and cloth-filtered Concentrated sweetwater cators. Clear concentrated sweet(mixed with No. 3 re300 The danger of large sucrose losses through inversion, under water melt sugar) and clothfiltration affination filtered acid conditions, is well established, and recent developments Second sirup 81 450 Above products---once in the study of true alkalinity and of hydrogen-ion concen- Second filtration concenchar-filtered trated sweetwater 78 200 1, tration have shown that titrations as made with common Products of 2nd, 3rd, and indicators are extremely misleading as a means of determining 4 t h char filtrations of No. 5 liquor 83 affination sirup, concenalkalinity or acidity. For these reasons, therefore, this No. 55 liquor 85 trated sweetwater, and 20 88 company in 1922 started a study of the whole subject, which No. 555 liquor No. 3 remelt sugar liquor ultimately led to the adoption of a very simple and effective Products Enlering and Leaving Char Filters system of alkalinity control based upon the determination of Clear raw liquor 20 Cloth-filtered raw liquor Water Double char-filtered raw hydrogen-ion concentration. Although considerable work Cube liquor liquor Once char-filtered raw has been done upon hydrogen-ion concentration as applied No. 1 liquor 99 liquor to the sugar industry (notably by Brewster and Raines of the No. 2 liquor Char-filtered granulated 96 sirups and remelt sugars 93 Louisiana Experiment Station), and this method of express- No. 3 liquor Result of multiple-char filtration of low-grade ing alkalinities is gradually spreading in the sugar world, the materials (aff. sirup, 90 present study was developed along lines particularly adapted No. 4 liquor concentrated sweetwater. and No. 3 remelt to practical refinery operations, and i t is believed that a brief sunarl - . history of the development, and some of the results secured in M 'isccllaneous P a n Prbducts 96.5 3.0 Centrifugal sirups from 1 granulated sirup No. its progress, will be of interest to those engaged in the sugar No. 2 granulated sirup corresponding grades 92.0 2;. ,, the 89.0 of granulated masseNo. 3 granulated sirup industry. 84.0 40:O cuites No. 4 granulated sirup The study started with an investigation of the reliability of Solutions of remelt sugars 15.0 obtained from a straight the ordinary methods of titration for sugar products and of the No. 1 remelt sugar liquor 95.0 89.0 40.0[ remelt boiling system. 2 remelt sugar liquor o . , 2oo.o All derived from prodinterpretation of the results, and led naturally to a brief investi- No. NO. 3 remelt sugar liquor ucts t h a t have been

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1 Presented before the Division of Sugar Chemistry at the 70th Meeting of the American Chemical Society, Los Angeles. Calif., August 3 t o 8, 1925.

No. 1 remelt sirup No., 2 remelt sirup

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originally char-filtered Centrifugal sirups from remelt massecuites

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INDUSTRIAL AND ENGINEERING CHEMISTRY

It will be noted that these products differ greatly in the amount of nonsugars present, as indicated by the varying purities, and also in the character of the nonsugars as a result of the v a r Y k degrees of char filtration received. This would be expected to result in the Presence of greatly differing amounts of weak organic acids and salts, which through their buffering action would not Ody cause errors in the end points when titrating with common indicators, but would caus'e these errors to vary greatly in the different products, making proper interpretation of results impossible. I n order to determine how great these errors were and what would be the most satisfactory indicator to use in sugar titrations, all the regular refinery products Were titrated over a Period of about one month with three indicators-Phen01phthalein, litmus, and bromothymol blue-and also titrated to true neutrality (PH 7) by means of an electrometric apparatus. Table 11 shows the averages of these tests for each product. It will be seen that there is no constant between the results secured with the different indicators when used with the different products. These differences are still more clearly brought out by the accompanying graphic chart, which shows the extent of the error when using these three indicators. It is evident that the use of either of the common indicators, phenolphthalein or litmus, may introduce large errors, andwhat makes them really objectionable-these errors vary greatly with the different products. For example, with raw liquor, phenolphthalein and litmus show opposite errors of 0.001 and 0.002 per cent, respectively, making a total difference of 0.003 per cent, while with clear affination sirup theseindicators show opposite errors of 0.022 per cent and 0.013 per cent, a total difference of 0.035 per cent. (It is to be noted that the error is greatest with products of low purity, and for products of similar purity is greatest for those which have received the least char filtration.) It is also evident that bromothymol blue gives practically accurate results with all products. It appeared quite definite from these results that phenolphthalein and litmus are actually misleading when used for alkalinity determinations of cane-sugar products. The immediate conclusion, of course, was that bromothymol blue was a much more satisfactory indicator to use. For a short period, therefore, until the use of hydrogen-ion measurements was started, this indicator was put into use at the C. & H. refinery as the standard for practically all alkalinity work. I

Vol. 17, No. 12

Relation between Titrated Alkalinity and Hydrogen-Ion Concentration

The foregoing results emphasized the fact that there were large and varying quantities of buffer substances present in cane-sugar products, which would tend to make all titrations, even with reliable indicators, of little value in determining the degree of activity of the acids or alkalies present. Investigation of recent years has brought out the fact that inversion of sucrose and decomposition of glucose in solution are dependent chiefly on the degree of activity of the acids or alkalies present-that is, upon the hydrogen and hydroxylion concentration-rather than upon the total acidity or alkalinity. For this reason it would appear that titrations for total alkalinity or acidity did not offer the proper control for minimizing inversion of sucrose and ~ecompositionof glucose. T~ determine what the titrated total and acidities actually meant in terms of active alkalinities and acidities, a number of the standard products were tested for hydrogen-ion concentration as a routine matter for a short period, as as being titrated. The hydrogen-ion concentration was determined a t first by color comparison with buffer solutions in tubes, and later by spot tests. The averages of these results are shown in Table 111. Table 111-Relation

between Titrated Alkalinity a n d H-Ion Concentration Titrated alkalinity PRODUCT (bromothymol blue) pH Raw liquor 8.25

-0.010

8.50 8.25 6.50 6.00 6.20 6.8 6.4

+0.002 f0.003

7.3 7.25

Cube liquor No. 4 liquor No. 4 sirup No. 55 liquor No. 5 liquor Second filtration concentrated sweetwater Clear affination sirup Affination green sirup

- 0 015

-0.010 -0.001

-0.048

5.60

This list gives some indication of the lack of uniformity in the relationship between total alkalinity or acidity and H-ion concentration. For example, an acidity of 0.001 per cent in cube liquor gives practically the same hydrogenion concentration as ten times as great a titrated acidity in No. 5 liquor, while an alkalinity of 0.001 per cent in cube liquor has a much higher activity (about ten times the hydroxyl-ion concentration) than three times as great a titrated alkalinity in clear affination sirup. To develop this point better, a number of different types of sugar products were made up to definite total acidities

Table 11-Comparative

Alkalinities of Refinery Products w h e n Titrated w i t h Phenolphthalein, Litmus, Bromothymol Blue, a n d Electrometrically (Expressed as equivalent percentages of CaO) (+ signifies alkalinity, acidity) --ALKALINITIES A S DETERMINED ERROR With With bromoBromoElectrophenolWith thymol Phenolthymol metrically phthalein litmus blue phthalein Litmus blue PRODUCT -0.082 Acid -0.052 -0.034 ? -0.004 Affination green sirup -0.048 -0.049 -0.028 ? fO.001 -0.050 -0.078 Affination wash sirup Acid - 0.022 +0.013 -0.001 -0.019 f0.016 +o.ooz 10.003 Clear affination sirup -0.022 fO.009 +0.001 Neutral -0.022 f0.009 $0.001 Clear concentrated sweetwater Second filtration concentrated -0.015 +0.002 -0.017 fO.009 0.000 sweetwater fO.002 fO.011 -0.012 +0.010 -0.022 -0.007 No. 5 liquor -0.010 Neutral +0.003 -0.010 -0.001 f 0 . 00s 0.000 -0.001 -0.011 +O. 007 No. 55 liquor No. -0.007 Neutral f0.007 0.000 -0.007 10.007 . .. 555 ...liauor Neutral +0.002 0.000 f0.001 Neutral f 0 . 001 4-0.003 -0.001 Clear raw &uor -0.001 +0.001 0.000 fO.001 f0.003 +0,002 Cube liquor (average) f 0 . 002 -0.001 +0.001 0.000 Neutral +0.002 fO.001 +0.001 Cube liquor (special sample) 0.000 -0.001 -0.002 Neutral -0.001 f0.001 Cube liquor (special sample) -0.001 fO.002 0.000 -0.002 -0.002 +0.002 Neutral Neutral No. 1 liquor 0.000 -0.004 +0.003 Neutral -0.004 +0.003 No. 2 liquor Neutral 0.000 + O . 004 Neutral -0.004 -0.004 No. 3 liquor -0,004 -0.008 -0.006 +0.002 +0.010 -0.005 -0.013 -0,021 No. 4 liquor -0.015 +0.002 -0.002 0.000 -0.. 002 +o. 002 Neutral No. 1 granulated sirup Neutral +0.001 -0.004 +0.003 Neutral No. 2 granulated sirup -0.001 -0.005 f0.002 -0.002 -0.005 f0.004 0.000 -0.002 -0.007 +0.002 No. 3 granulated sirup -0.010 fO.010 0.000 -0.014 -0.024 Neutral -0.010 No. 4 granulated sirup +o. 009 +0.001 t-0.007 -0.001 -0.007 -0.002 -0.009 No. 2 remelt sugar liquor 4-0.015 0.000 -0.007 -0.040 -0.022 -0.018 No. 3 remelt sugar liquor -0.022 -0.036 -0.017 4-0.005 -0.002 -0.015 -0.051 -0.010 No. 2 remelt sirup

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INDUSTRIAL A N D ENGINEERING CHEMISTRY

December, 1925

and alkalinities by adding definite quantities of N/28 sulfuric acid and N/28 sodium hydroxide to the neutral solutions. The hydrogen-ion concentrations of these products are shown in Table IV. Although only strong acids and alkalies were used in these tests, the results show very strikingly the effects of the buffer substances that are normally present. It is clear from this

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As inversion of sucrose and decomposition of glucose, both of which are of great concern to the sugar refiner, are so dependent on hydrogen-ion concentration, the conclusion is obvious that titrations are practically worthless as a means of refinery alkalinity control, and that some convenient means of hydrogen-ion control is necessary. For this reason, as explained in a later section of this paper, a very rapid and accurate means of determining hydrogenion concentration was developed for use in the plant control. Development of Acidity in Refining Process

It was formerly the custom to lime only one or two products a t the beginning of the refining process, letting others take care of themselves. As the liquors and sirups, in going through the refinery, are continually under the influence of heat and therefore subject to the development of acidity through decomposition of glucose, i t was thought best to make a survey of the plant to determine if it were not necessary to lime many more products. As might be expected, i t was found that there was a development of acidity all along the line. Table V shows the more important changes that were found to take place as the liquors passed through the plant. in H-Ion Concentration while Passing through Refinery pH RBSULTI?W PRODUCT PH Unfiltered raw liquor 7.35 Cloth filtered raw liquor 7.2 Raw liquor entering char 7.2 No. 1 liquor 7.0 Granulated sirup mixture No. 2 liquor 6.5 7.2 entering char No. 3 liquor 6.3 Clear affination entering char 7 . 2 No. 555 liquor 6.7 Average of all liquors entering 7.0+ Char sweetwater 5 . 5 t o 5.76 i. char Products boiled in No. 1 reNo. 1 remelt sugar 6.65 6.9 melt massecuite No. 1 remelt sirup 6.40 No. 1 remelt sirup boiled into 6 . 4 No. 2 remelt sugar 6.20 L.* No. 2 remelt massecuite No. 2 remelt sirup 5.95 No. 2 remelt sirup 5.95 No. 3 remelt sugar 5.a5 Table V-Changes

ORIGINAL PRODUCT

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€ f , f In parrtnt Chart S h o w i n g Indicated Alkalinity or Acidity of Refiner Produ c t s as D e t e r m i n e d w i t h L i t m u s , P h e n o l h t h a l e i n , a n d Bromot h y m o l Blue w h e n the Products Are i n Cond;tion of T r u e Neutrality as Determined by E l e c a o m e t r i c Apparatus

tabulation that there is no uniform relationship between the total alkalinity and the hydrogen-ion concentration of the various refinery products-nothing that would make it possible to judge of one from the other. For example, raw liquor, with an acidity of 0005, shows a p H of 5.26 (sufficient to cause a very active inversion), whereas affination sirup a t the same acidity shows no measurable change of the hydrogen-ion concentration. Those familiar with refinery practice know that there are large seasonal variations in the character of the products. These are due in part to changes in the character of the raw sugar, which presumably come as a result of changes in the cane as the season progresses, and in part to variations in the refinery operation. For example, changes in the rate of melt almost necessarily mean changes in the intensity of char filtration, this, of course, greatly affecting the character of the final products, particularly the amount of the buffer substance left in them. Therefore, this irregularity of relationship between total alkalinity and hydrogen-ion concentration must exist, not only between different products, but also, to some extent, between similar products at different times. Apparent punty coefficient +0.050 99

PRODUCT No. 1 liquor Raw liquor No. 4 liquor No. 55 liquor No. 2remeltsugarliquor Concentratedsweetwater Affination green sirup No. 2 remelt sirup

+

80

80 56

Although all the refinery products are not listed, merely those that illustrate the point, it is clear that there is a development of acidity in all the refining processes where liquors undergo heat. I n order to minimize inversion without securing excessive decomposition of invert sugar, i t is generally considered good policy to keep liquors as close hs possible to p H 7.0. It will be seen that quite a number of products show a distinct drop below that point-particularly the char sweetwater and the remelt products. As a result of these observations, therefore, in laying out the system of control, provision was made for neutralizing acidities in entering products as soon as possible and thereafter neutralizing any marked acidity that developed as the material passed through the house. Establishment of Refinery Alkalinity Control

The main object of alkalinity control in a sugar refinery is, of course, to minimize inversion of sucrose. This, however, should be done in such a way that there is the smallest possible destruction of glucose and the smallest possible introduction of lime. It is believed that this result can be best secured by keeping all the products at or close to neutralitythat is, a t a pH of 7.0. As was explained earlier, an attempt

Concentration (pH) at Various Total Alkalinities

Alkalinity, Per cent CaO f 0 . 0 2 0 +0.010 +0.005 +0.002 +0.001Neut. -0.001 -0.002 5.50 6.00 8 . 7 5 8 . 50 7.00 9.50 6.00 6.50 8.25 7.50 7.00 9.50 9.00 10.0 9.00 8.60 8.00 7.25 7.10 7 . 0 0 6.75 6.50 9.65 8.75 8.25 7.35 7.15 7 . 0 5 7.00 6.90 6.75 9.25 8.35 7.50 7.25 7.10 7.00 7.00 7.00 6.90 9.00 8.25 7.25 7.15 7.00 7.00 7.00 7.00 7.00 8.35 7.50 7.25 7.00 7.00 7.00 7.00 7.00 7.00 8.35 7.50 7.25 7.05 7.00 7.00 7 . 0 0 7.00 7.00

::+ 85 89

Table N-H-Ion

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-0.005 4.25 5.25 6.25 6.40 6.60 6.90 7.00 7.00

-0.010-0.020 4.25 5.90 6.00 6.00 6.75 6.90 6.90

5.25 5.75 5.75 6.50 6.75 6.60

-0.050-0.100 4.50 4.75 5.25 6.00 6.25 6.00

4.25 5.50 5.50 5.60

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to maintain alkalinities above this point merely results in decomposition of glucose with a resulting drop in alkalinity, which causes an unnecessary increase in lime salts, whereas below this point the rate of inversion of sucrose increases rapidly. I n order to establish a system that would accomplish these desired results, it was considered necessary that the following requirements be satisfied : 1-A quick, easy, and accurate means of determining the hydrogen-ion concentration of refinery products should be available. 2-Provision should be made for making frequent tests on practically all products throughout the plant. 3-Provision should exist for liming as many products as necessary and for accurately controlling the addition of lime. I-Method of making hydrogen-ion test. The first of these requirements was the most difficult t o satisfy in a really practical way. The extremely accurate laboratory method (with the use of electrometric apparatus) was, of course, too cumbersome for consideration. Colorimetric tests made by adding indicators t o diluted samples of su ar products in tubes were more rapid, but the natural colors o f the solutions diminished the accuracy of the results. The test finally adopted was a spot test, bq which a few drops of the product t o be tested (properly diluted, if necessary) are put into each of three depressions in a porcelain spot plate and appropriate indicators added-phenolphthalein, bromothymol blue, and methyl red. The great difficulty was to find satisfactory color standards for comparison. The use of buffer solutions as standards was too slow and cumbersome t o permit of making many tests, and the published color charts were so dull and lusterless that they offered no proper comparison with bright-colored solutions on a test plate. After much effort a satisfactory color chart was prepared, in collaboration with a n expert in photographic tinting, by t h e use of dyes on gelatin-coated celluloid. To make this chart, a sheet of gelatin-coated celluloid must be carefully dyed exactly to match the hue and intensity of color of the indicators a t each hydrogen-ion reading it is desired t o duplicate. I n all, a series of thirty-one sheets was prepared representing the colors of phenolphthalein, bromothymol blue, and methyl red, ranging from p H 10.0 t o p H 4.5, at intervals of 0.25 pH. The use of this chart has so simplified the test t h a t i t is possible for one man t o test as many as thirty products per hour, scattered throughout the plant, easily and accurately. 2-Provision f o r frequent tests throughout the refinery. As it was apparent t h a t the alkalinity control would have to cover practically the entire plant, and not one or two stations only, a number of testing hoods were installed a t the various stations. These are small cabinet-like structures, curtained off from ordinary light sources, and provided with daylight lamps and with color charts, glassware, and all ’reagents and equipment necessary for testing the products. Seven of these “miniature laboratories” are provided, so distributed t h a t all products may be tested without delay. To cover this work properly, a n alkalinity controller-generally a young chemist-is provided on each shift, whose duty it is t o make his rounds of the house each hour, testing all products t h a t are limed, and also a number that are tested for record purposes only. 3-Liming equipment. I n order t o permit of proper liming, it is necessary t h a t the lime be easy to regulate, be continuous in application-as most refinery products are handled continuously rather than intermittently-and be distributed over the entire house. The first of these conditions was secured by working with very thin lime-2’ Brix. It is almost impossible t o secure accurate regulation with heavy lime, the result usually being either excessive or i n s a c i e n t liming. It is found t h a t thin lime permits of very exact regulation. The second and third conditions were met by installing a circulating system by which this thin lime is circulated throughout t h e refinery, wherever products are limed. Valves and drops are provided for all tanks in which lime may be required.

Work on the development of this control was started in 1922, and the system, as described above, was in complete operation about the middle of 1923. I n operation it is very simple. The alkalinity controllers make their rounds a t regular intervals, testing the various products and recording the results so that they are available to the operators and foremen a t all times-calling attention,

Vol. 17, N o . 12

of course, to any unusual conditions. The operators regulate the flow of lime to the various products EO as to maintain the hydrogen-ion concentrations very close to pH 7.0. At a few stations, where close control is required, the operators make additional tests. The following list gives a general idea of the products that are tested, the tests on the different products being made a t intervals varying from a half hour to four hours, depending on the product tested:

(4)

(5) (6) (7)

Raw liquor and affination sirup a t the melt All products previous to cloth filtration All products entering and leaving char filters Pan liquors and pan sirups Sweetwaters from cloth filters Sweetwaters entering and leaving evaporators Remelt sugar liquors

Kot all of these products are limed, as it would be undesirable in some cases-as, for example, wben a liquor is to be boiled directly into granulated sugar. The following list shows in a general way the products that are limed:

(I) Affination wash sirup used for mingling raw sugar ( 2 ) Raw liquor at the melt (3) All products a t the blow-ups previous to cloth filtration (six products in all, most of them falling into two-classifications-smear and pressure liquor) (4) Products entering char filters (limed occasionally, when p H gets low) ( 5 ) Remelt sugar liquors (6) Sweetwater entering the evaporators (7) Sweetwaters and sludges from sweetland filters previous. t o filtration over Oliver filters

All these products are maintained continuously a t a hydrogen-ion concentration close to pH 7.0, except the sludges from the Sweetland presses; these are maintained much more alkaline-pH 8.0 to 9.0-40 facilitate filtration. The value of this control may be appreciated when it is realized that the introduction of lime into process has been reduced from a former figure of about 150 pounds per 100. tons melt (0.075 per cent) to about 75 pounds per 100 tons melt (0.037 per cent), this materially reducing the burden on the char and reducing molasses production. The main advantage, however, has been the fact that with this small introduction of lime it has been possible to maintain nearly all the products in the refinery in a neutral or slightly alkaline condition, whereas formerly, even with a large consumption of lime, there were many acid conditions throughout the house. Suggestions for Future Work The details of liming-which products to lime, the alkalinities desired, and the means of application-are, of course, all matters that each plant must settle for itself. However, the methods of testing for alkalinity of sugar products which have been developing rapidly in recent years are a matter in which all sugar producers and refiners are equally interested. As comparatively little of this work has been published and none of these newer methods have found their way into the sugar textbooks, it is believed that a study of the various methods developed would be of great help to the sugar industry, not only in the exchange of viewpoints that would result, but in a t least some standardization of methods that would make it possible for chemical supply houses to stock satisfactory standard equipment. It is therefore suggested that the Bureau of Chemistry be asked to correspond with those who have done work on this subject and subsequently publish the details of the various methods that have been or may be developed. This may make it possible ultimately to secure the adoption of the most satisfactory methods as standard throughout the industry.