944
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 14, No. 10
Sugar Purity Determinations' By W.D. Rome 175 PARKAvE., YONKERS, N. Y.
The following paper describes a method of making sugar purity determinations which can be carried through in not over 60 per cent of the time required for the wet lead method. The paper describes a special spindle for making Brix determinations in which temperature corrections can be read directly from the instrument. Clarification is accomplished with a specially prepared dry lead powder, eliminating the measurement of exactly 100 cc. and dilution to exactly 110 cc. The paper ends with the description of a table for reading sugar purities, knowing Brix ualue and polarization. The method eliminates seueral common sources of error, thus improving quality as well as quantity of the work done in the sugar laboratory.
tion noted, a portion of the solution clarified with subacetate of lead solution and polarized, and the sugar determined from a table giving the percentages of sugar for the various degrees Brix and the various polarizations. The ordinary polarization thus found is divided by the Brix, uncorrected for temperature, to find the apparent purity. I n Casamajor's method the calculation is modified so as to give the apparent purity directly without the intermediate finding of the percentage of sugar in the solution, for in ordinary house control the purity is the figure needed. Casamajor developed the formula:
N SUGAR manufacture and refining no analytical determination is of such importance as that of the purity. All masseouites are adjusted in purity to the proper degree go that the desired quality of sugar may result, the proper yield be obtained, and the treated material fit in as it should with what precedes and what follows it. Sirups or molasses must be tested for purity t o determine that the proper ratio exists between them and the massecuites from which they spring. A useful factor is the concentration of impurities in sirup as compared with that in the massecuite. Of course, (100-purity) gives the impurities, and it will be immediately apparent that the ratio of the impurities in the massecuite to the impurities in the sirup is a fairly constant factor for similar grades of massecuites. Since these factors progressively lessen as the purity of the massecuibe goes down, it will be found a very useful aid in calculating the steps and yields in any proposed procedure in purification by crystallization. Liquors from boneblack filters must be watched carefully as to purity to allow of proper segregation. So must sweet waters from bags, presses, char filters, or other source, in order to control operations and distribution. Raw sugar ailhation must also be very closely checked by purity determinations in order to insure sufficient, and to prevent excessive, washing in the centrifugals. In a large plant, purity determinations form the main guide for chemical control and mount into the hundreds daily. The tests must be made quickly and with such accuracy as is compatible with speed. The procedure must be made as simple as possible.
Degree Brix X specific gravity = Factor
I
CALCULATION OF PURITY The two requisites to calculate the purity of a sample are its percentage of solids and its percentage of sugar. When the solids are determined by evaporation and the sucrose by double polarization, the purity obtained is known as the true purity; when the solids are determined by the gravity of the solution, whether through the pycnometer, the hydrometer, the Westphal balance, or the refractometer, and the sugar by single polarization, the result is called the apparent purity. This is the usual test and there are several ways of performing it. By Schmidt's method, largely used in European beet practice, the density of the solution is determined by a Brix hydrometer, the temperature correc1 Presented before the Division of Sugar Chemistry at the 63rd Meeting of the American Chemical Society, Birmingham, Ala., April 8 t o 7, 1922.
26.048
This factor, multiplied hy the polarization, gives the apparent purity. Such factors, calculated for the various demees Brix and the intermediate tenths. are arranged in a taglo for ready use, and a further development consists in a table or set of tables giving the corresponding apparent purity for every tenth of a degree Brix and each tenth of a degree polarization. Some operators take the time and trouble to bring the solution being tested to the normal temperature before determining the degree Brix. If such a solution is also polarized at the same temperature, no error due to effects of changing temperature upon density and specific rotation can creep in. As the errors in polarization are very small for R slight temperature range, they are generally neglected, on account to the great inconvenience and loss of time incurred in bringing solutions'exactly to a normal temperature. The usual manner of determining the apparent purity is to find the degree Brix with a hydrometer in a tall glass cylinder, to observe the temperature of the solution, to clarify the solution with subacetate of lead, filter and polarize, and to calculate the purity from the corrected Brix and the observed polarization. RAPID
DETERMINATION O F PURITY
The following method 'developed by the writer for obtaining results rapidly and simply may be of use to others. DENSITY-For rapid Brix determinations a specially constructed spindle, which combines several novel features, has been evolved. The spindle is about 30 em. over all, with a stem about 15 em. long. This contains a scale of about 11 em., covering 8 full degrees divided into tenths, each of which is just about equal to the depth of the meniscus of the solution. The lower part of the spindle is made almost plainly conical to give greater strength in resistance to breakage,
Oct., 1922
.
Brix.. . . l5,l (Factor). (1.6221
.
THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY 15.2 1.6108 40.27 40.43 40.59 40.75 40.91 41.08 41.24 41.40 41.56 41.72 41.88 42.04
l5,3 1.5996
l5,4 1.5887
TABLE OF 15.5 1.5777
39 I99 40.15 40.31 40.47 40.63 40.79 40.95 41.11 41.27 41.43 41.59 41.75
39.72 39.88 40.04 40.19 40.35 40.51 40.67 40.83 40.99 41.15 41.31 41.47
39.44 39.60 39.76 39.92 40.07 40.23 40.39 40.55 40.70 40.86 41.02 41.18
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S U G A R PURITIES
to increase the area of the thermometer bulb, so as to quicken its action, and to give ease in washing and wiping this part of the instrument. A new departure has been made in the scale of this thermometer. Centigrade degrees are shown from 10” to 35”, with 20” taken as the normal temperature, PO as to cover all practical ranges, but these degrees are marked off well to one side. Immediately adjacent to the mercurial column are two direct temperature correction scales, showing in tenths of a degree Brix the temperature corrections to be added to ’or subtracted from the direct readings on the Brix scale. On one side of the mercury column are the temperature corrections applicable for density at the top of the Brix scale; on the other side are the corrections for readings a t the bottom of the Brix scale. These corrections differ quite materially, so that a single temperature correction scale is very deceptive and leads to considerable errors in purity determinations. An interesting thing about this “Complete Temperature Correction Scale” is its rapid visibility, for just as one measures a t a glance the relative position of the level of the liquid between the top and bottom of the Brix scale, so he intuitively arrives a t the corresponding point between the maximum and minimum temperature corrections, which is to be taken and applied to the particular density reading obtained. I n practice the matter is very simple, for usually the Brix is made up arbitrarily to lie quite near one end of the scale. An 8 to 16 Brix spindle is used for the general run of solutions that are rather dark and readings are taken between 15 and 16 Brix, while for lighter colored solutions a 16 to 24 spindle is frequently employed, and solutions are prepared to be read a t the end representing the greater density. Readings are always made to the closest half-tenth, and where unusual accuracy is desired the readings can be made to about a hundredth of a degree by interpolation. Equally close readings can be made on the temperature correction scales. CLARIFICATION-The density having been obtained, the next operation, that of clarifying the solution for polarization, is greatly expedited by the use of the author’s “dry lead” method, in which specially prepared anhydrous lead subacetate is employed in place of basic lead acetate solut.ion. As this dry powder effects the same clarification without producing any alteration in the concentration of the sugar solution, the tedious and frequently inaccurate method previously followed can be greatly simplified. Instead of measuring off 100 cc. of the solution, adding lead solution and making up to 110 cc. with water before filtering, one simply throws out all but about 100 cc. of the sugar solution from the Brixing cylinder, adds with a little scoop a small amount of the “dry lead” powder, sufficient to cause flocculation (each 0.1 cc. of the dry lead is equivalent to 2 cc. of a28” Brix solution of the subacetate), turns the cylinder over two or three times, and pours all directly upon a filter paper. Since no correction need be added to the polarization, as was formerly the case to compensate for the dilution of the solution, a source of frequent error is eliminated. POLARIZATION-FOT polarizing, a continuous tube is a convenience and saves time, and is good if the solutions
15.6 1.5670
15 7 1.5564
15.8 1.5458
15.9 1.5355
16.0 1.5253
16. I 1.6152)
39.18 39.33 39.49 39.65 39.80 39.96 40.12 40.27 40.43 40.59 40.74 40.90
38.91 39.07 39.22 39.3s 39.53 39.69 39.84 40.00 40.16 40.31 40.47 40.62
38.65 38.80 38.95 39.11 39.26 39.42 39.57 39.73 39.88 40.04 40.19 40.35
38.39 38.54 38.69 38.85 39.00 39.16 39.31 39.46 39.62 39.77 39.92 40.08
38.13 38.29 38.44 38.59 38.74 38,90 39.05 39.20 39.35 39.51 39.66 39.81
37.88 3.03 38.18 38.33 38.49 38.64 38.79 38.94 39.09 39.24 39.40 39.55
are of nearly the same density, but when the densities of successive solutions change as radically as they do in refinery practice, the intermittent tube is safer. Covering ends that slide on, however, are to be preferred to those which have to be screwed on. CALCULATION-There remains only the calculation, either by multiplying the polarization by the factor corresponding to the Brix, or by determining the product in some easier way. Various tables and a number of mechanical devices have been constructed for aiding in this operation. The one which the’writer has found most convenient for the great majority of solutions tested is a long narrow table of figures giving all the purities corresponding to the different tenths of a degree Brix between 15 and 16 Brix or between any other two consecutive degrees, and the different tenths of a degree by the polariscope. The Brix readings head the vertical columns, while the polariscopic readings stand opposite the horizontal rows of figures. Such a table is about 25 cm. wide and nearly a meter and a half long. This would be quite unwieldy if it had to be used fully extended, and it would be a little inconvenient and subject to excessive wear if it were divided into pages in book form. A very convenient arrangement which was devised many years ago, however, has proved fully satisfactory. The long paper strip is mounted on two wooden cylinders about 10 cm. in diameter and a little longer than the width of the paper strip. An end of the paper is tacked to each cylinder, and the cylinders are rolled until about half of the strip is wound upon each cylinder and a plane 20- to 22-cm. stretch of paper stands between the two. I n this position the whole is mounted in a glass-fronted box and set up in a convenient position for the operator to use. Prior to assembling, each cylinder is bored out longitudinally and a Hartshorn spring shade roller inserted in each, in opposite direction? and with ratchets removed. Each spring is given a fairly good tension, so that they tend to pull the two ends of the panoramic roll away from each other, and the whole system remains in practical equilibrium, no matter to which position the paper sheet may be brought. A small windlass handle protrudes from the center o€ the end of one of the cylinders through the side of the encasing box, so that the operator easily gives it a turn or two so as to expose whatever part of the table he wishes to bring into view. This device gives great satisfaction to the operators and appears to have suffered no appreciable deterioration after long years of constant use. A part of the table of sugar purities is shown herewith.
According to Drug and Chemical Markets, the British dyestuff s licensing committee proposes t o support the domestic dye industry by refusing import licenses when domestic dyes are available in adequate quantities and a t reasonable prices. Reasonable prices are considered to be three times the pre-war prices of dyes in general. With regard to vat dyes, reasonable prices for indigo dyes will be two and one-half times and for other vat dyes, five times pre-war prices.
