INDUSTRIAL AND ENGINEERING CHEMISTRY
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and to diminish the time required for the analysis. The method of Braidy is preferred to t,he Fehling's solution procedure. In both methods the analytical part of the determination requires a long time and complicated apparatus. Moreover, the copper values may differ largely from the true reducing figures, as the cellulose itself is attacked by the caustic solution and the time of boiling is too short for complete oxidation of the original impurities.
Vol. 20, No. 11
Giitze's method to determine silver numbers is reviewed and applied to bleached sulfite pulps. A suitable apparatus and some changes are advised. The results show that after 24 hours the reaction is nearly completed and that the values will be much nearer to the true value than the copper numbers. Moreover the manipulations of the analysis are much simpler, standardization is less necessary, and the results are more accurate.
Determination of Solubility of Sucrose in BeetHouse Sirup' R. J. Brown, J. E. S h a r p , a n d H. W. Dahlberg GREATWESTERNSUGARCOMPANY, DENVER, COLO.
A m e t h o d for obtaining t h e solubility of sucrose in L A S S E N 2 has shown A low-purity molasses of beet-sugar sirups has been described, a n d results a n d that the solubility of known composition was taken comments using t h i s m e t h o d have been given. sugar in impure soluas a starting point for the The basing of t h e solubility d e t e r m i n a t i o n s on an tions depends on the nature work, and from it various original molasses analysis a n d on d r y substance deterof the impurities present. It solutions of known impuritym i n a t i o n s on the s a t u r a t e d s i r u p s has been shown to is therefore to be expected w a t e r ratio were prepared. decrease t h e labor a t t e n d a n t to s u c h determinations that the solubility of sugar These solutions were satua n d to offer a simple m e a n s for e s t i m a t i n g the accuracy in siruns from different terrir a t e d w i t h sucrose a t the tories will vary. In addition of the original results. proper temperature and withto the effect of climate and out the loss of moisture. It is a t once evident that the purity and sucrose content soil, important changes in re1at)ivecomposition of impurities take place during the refining process. Certain classes of sub- of these saturated solutions can be calculrtted from their dry stances which are present in the defecated juices are constantly substance, thus greatly reducing the amount of analytical being eliminated, and others concentrated, as the low-purity wo-k required. The results thus obtained may readily be sirups pass through the Steffen or other molasses desugarizing plotted in such form that regularity of the curves gives a cycles. This change is roughly measured by the change in measure of the accuracy of the data, provided the original raffinose content, stated as per cent raffinoseon total impurities, analysis of the molasses and dry-substance determinations which varies from 5 per cent to 50 per cent in sirups handled on individual samples are known to be accurate. by the processes employed in the Rocky Mountain region. PROCEDURE-sirups of predetermined water-impurity ratio Practically all the published data on the solubility of sugar were prepared from a given molasses and placed in brass drums, in beet sirups are based an determinations made under Euro- fitted with small brass caps. Sufficient sucrose was added to pean conditions and cannot be applied to sirups encountered almost saturate the solution at 40' C. The drums were then completely submerged in a thermostatically controlled in this country. Since a knowledge of the solubility of sugar closed, water bath, and rotated slowly until all the sugar had dissolved. in the sirups is necessary for the intelligent and efficient con- The caps of the drums were then removed and sufficient screened trol of the crystallization processes, it has been deemed ad- "Confectioners' A" sugar was added to insure the presence of visable to determine these data for the sirups encountered in excess crystalline sugar under all conditions. The bath was adjusted to the proper temperature and the this region. drums were rotated long enough to saturate the solutions. It is proposed to determine the solubilities over a temper- Samples were then removed and the temperature was raised ature range of 40" to 80" C. on sirups of varying content and slightly for 24 hours and then lowered to the original point and held there until equilibrium had again been reached. The composition of impurities. sirups were again sampled, the drums closed, and the temperature At the present time a method of procedure has been devised raised IO" C. for the next determination. In this manner and that part of the field has been covered which is repre- solubility results were obtained approaching equilibrium from sented by sirups containing a low ratio of raffinose to im- undersaturation and suoersaturation. The temperature was controlled by means of a mercurypurities, such as are encountered in non-Steffen factories. thermostat operating a dual electrical heating system. The data given in this paper will be supplemented from time column Owing to the large fluctuations in room temperature and the to time as the work progresses. wide range of temperatures which were used in the solubility
C
Method
The most difficult problem facing t h e investigator in this field is the accurate determination of sucrose in the saturated solutions. The accurate determination of sucrose by direct analysis is a tedious procedure, and since in any event a drysubstance determination on the sirup examined is required in order to determine the purity, a method was adapted by which the purity of the saturated solutions could be calculated from the dry-substance determination alone. 1 Presented before the Division of Sugar Chemistry at the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 18 to 19, 1928.
$2.Vn. dcut. Zuckmind., 64, 807 (1914).
determinations, a large heater furnishing automatic rough temperature adjustment and a smaller heater for the purpose of fine adjustment were used. The thermostat was able to keep the temperature of the bath constant within 0.02" C. over unlimited periods of time. In sampling the sirups the drum cap was replaced by a sampler consisting of a cap pierced by two tubes. One tube was of copper, and t o the end extending into the drum was attached a disk made of two sheets of monel-metal iilter cloth. This disk was submerged below the level of the liquor in the drum. Air pressure was applied at the second opening in the cap and crystalfree, saturated sirup was forced out of the drum into a flask surrounded by ice, t o reduce loss of moisture by evaporation t o a minimum.
The samples of sirup were analyzed for dry substance.
November, 1028
1-
INDUSTRIAL A X D ENGINEERING CHEMISTRY
JW
*oa
Parts D y Substance per 100 Parts .&terin
Sba
1231
bo0
Jaturated Solution
Figure 1-Concentration of Saturated Beet-Sugar Sirups. Temperature and Impurity-Water Ratio (Solubility at 0 impurities taken from Herzfeld)
Effect of Figure 2-Concentration
of Saturated Beet-Sugar Sirups. Solubility Isotherms
nearness of approach t o saturation of the sirups taken for analysis. At the beginning of the work various periods of time for permitting the solutions to reach equilibrium were granted. At 40" C. saturation was approached very slowly. It was found that if 4 days were allowed for approaching equilibrium from a rising and from a falling temperature, the dry substance content of the two samples of sirup checked within 0.1 per cent on sirup. The required time decreased with rising temperature, so that 24 hours at 80" C. were sufficient to give saturated sirups. Since the time required to make a complete run on a given sirup was somewhat long-ten samples being taken, two each Figure 3-Concentration of Saturated Beet-Sugar Sirups a t Varying a t 40°, 50", GOo, 70", and 80" C.-the question of decompoTemperatures and Purities sition of sugar due to continued heating became important. (Solubility at 100 purity taken from Herzfeld) This question was definitely answered when it was found that The impurity-water ratio and the total dry substance being two sirups taken from the same drum a t 80" C., the first known, the sucrose content and purity were calculated. sample before decomposition became appreciable and the Since the determination of dry substance was such an im- second after a marked decomposition had taken place, showed portant feature of the investigation, and since the working identical dry-substance content. Although the analyses of out of a satisfactory method was a problem in itself, a separate the samples by enzyme hydrolysis would not have shown the same sucrose coiltent, this fact has no influence on the solupaper on this subject has been p ~ b l i s h e d . ~ bility results. The decomposition products had the same effect on the solubility of sucrose as sucrose itself, so the soluAccuracy of Data bility as calculated from the original impurity-water ratio Owing to the nature of the materials handled, it is unlikely of the sirup is unaffected by the decomposition. It is underthat absolute accuracy in analysis of the products has been stood, however, that these decomposition products repreobtained, and it appears advisable to give some consideration sented only a very small percentage of the total sugar. to the sources of error and their probable magnitude. Since many samples were taken from a drum in the course The accuracy of the final results is. of course. dependent on of a single run, it was ne essary to obtain an estimate of the the accuracy of the analysis of the original molasses. This quantity of water lost through evaporation incidental to analysis was carried out by means of the double enzyme sampling. Determinations of losses from major sources hydrolysis as given by Paine and Balch4 and modified in this showed that evaporation was negligible, owing to the low laboratory to meet the present requirements. An extended vapor pressure of the saturated solutions, even at 80" C., investigation of the method of analysis led to the conclusion and to the short time that the drums were open to the atmosthat, while the sucrose and raffinose content as determined phere. by standard methods are constant to within 0.05 per cent, Errors may also result from contamination of the samples the absolute accuracy depends on the nature of the sirup with crystals of sugar either in the form of undissolved fraganalyzed. And it appears that, in the case of the molasses ments or as "smear" rcsulting from too rapid cooling of the under investigation, the sucrose content is probably about supersaturated solutiom Microscopic examination of the 0.25 per cent too low, while raffinose is correct. A detailed samples showed that the quantity of fragments of crystals discussion of these methods will be made the subject of a was neglibible. 111 one case too rapid cooling had caused the future paper. formation of n smear which passed through the screen of the The determinations of dry substance were made with sampler. Microscopic examination of this sample showed a great care and the error from this source is about =t0.03 large number of minute crystals, but the dry substance of per cent. this sample was only 0.2 per cent higher than the dry subNext t o the analysis of the solutions in importance is the stance of the sample taken a t the same point on a rising temperature. When no smear was formed the effect of sugar Brown, Sharp, and Nees, IND.ENQ.C x E x . , 20, 945 (1928). 4 I b i d . , 17, 240 (1925). passing through the screen did not enter into the problem.
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Examination of Results The results obtained on the various solutions of constant impurity-water ratio are given in Table I. Table I-Concentration IMPURITY-
....._RATIO
of Saturated Beet-Sugar Sirups
WAVW2
PER 100 PARTS WATER 60' C. 70' C. 80' C. 287.3 320.5 362.1 0.360 319.5 358 405 0.463 231 369.5 417.5 0.594 346 385 434 0.746 366 454 406.5 0.881 383 424 471 1,001 399 488 441 1.160 423 463.5 517 I.378 459 505 554 Solubility at 0.000 impurities taken from Herzfeld. ANCE
0 . onoa
For the purpose of calculating solubilities on the basis of purity of the sirups, and to obtain an idea of the relative accuracy of the results, they are plotted in three graphs. Figure 1 shows the solubilities of total dry substance a t various temperatures in different solutions of constant impurity-water ratio. The curve a t zero impurities (sucrose) is taken from H e r ~ f e l d . ~In Figure 2 the solubility isotherms have been drawn. The regularity of the curves in these figures is a measure of the accuracy of the results, and since there are no decided abnormalities, the results seem to have a satisfactory degree of accuracy. Certain small irregularities in the points do appear, but these are not serious. The greatest variations might be expected a t 80" C., since errors due,to destruction of sucrose and evaporation are cumulative
Vol. 20, No. 11
and greatest at this temperature. In Figure 2 it may be seen that the points on the 80" C. isotherm show the greatest irregularities, though they are relatively light. It i s noteworthy that the points representing 0.746 impurity-water ratio on the various isotherms fall to the right of their respective curves, the amount of the deflection decreasing with increasing temperature. The conclusion to be drawn from this is that a slight error exists in the impurity-water ratio recorded. An error in making up the original sirup would have a decrensingly smaller effect on the calculated solubility as the temperature was increased and greater amounts of sugar were dissolved. In no case does any determined point fall away from the smooth curve by R distance equivalent to 1 per cent error on total dry substance, and the curves themselves are probably correct within 0.1 to 0.2 per cent, except possibly a t 80" C. Here the error is certainly not much greater. Figure 3, concentration of saturated sugar solutions of a given purity, was prepared from Figure 2. The area in the lower right-hand section of Figure 3 will be filled in when sirups of higher impurity-water ratio have been examined. To complete the record the analysis of the molasses follows: Direct polarization Top-yeast polarization Bottom-yeast polarization Sucrose Raffinose Moisture Ash Undetermined
8 Browne, Handbookof Sugar Analysis, p. 649;2. V&. dcuf. ZuckPrind., 4a, 181,232 (1892).
True purity Per cent ra5nose on impurities
50.37' --16.16°
-17.19' Per cent 49.53 1.39 21.22 11.5 16.4 62.87 4.75
Carbon and Hydrogen Determinations Using a Metal Tube' S. Avery THE UNIVERSITY OR NBBRASICA, LINCOLN, NEBR.
INCB Liebig's initial investigations in ultimate organic analysis, glass tubes have been improved in qunlity from time to time. Porcelain and quartz tubes have acquired an extensive use, but in spite of some obvious advantages, little or no progress has been made in the use of metal tubes. This paper gives results obtained with metal tubes during the current year.
S
Metal Tubing Available The tubing should be inexpensive, not permeable to gases, able to withstand temperatures usually used for combustion analysis, and yield no impurities when heated in a current of oxygen. Nickel tubing satisfies these requirements except the last named, and it is quite possible that there is carbonfree nickel tubing on the market. Of the two nickel tubes tested in this laboratory, the amount of carbon dioxide given off from one was negligible, the other, however, gave results high in carbon, gradually decreasing as the tube was used. but careful qualitative tests always showed traces of carbon dioxide. A tube of nickel-copper alloy also showed slight traces of carbon. Tubes of copper were found free from this source of error. Although copper heated in air or oxygen oxidizes and scales, a tuhe of this metal may be used for a large number of determinations before it in materially affected. Plating a copper tube externally with nickel increases its life to a marked 1
Received April 5. 1928.
degree. Most of the determinations here recorded were made in such a tube. However, the combination of copper and nickel tubes described in the next paragraph is more satisfactory. Combustion Tube
A copper tube, */8- or llrinch (standard) iron pipe size (actual inner diameter 12.5 or 16.8 mm.), as a core protrudes about 3 inches (7.6 cm.) at each end from a thin, tightly fitting outer jacket of nickel held in place by friction. The nickel protects the copper from external oxidation and the inner coating of copper oxide formed is not inclined to scale off. The extreme ends of the tube are provided with water jackets. These may be turned out of any convenient metal, or made of sheet metal, and soldered or brazed to the protruding ends of the copper core. On account of the high conductivity of the copper in the combustion tube, water-jacketed ends are essential. They also permit the operation to be carried out with greater precision than when the ends are air-cooled in the ordinary way. Apparatus a n d Reagents Used in Connection with Metal T u be The sketch show8 the apparatus used. Copper oxide in wire form and oxidized copper gauze are placed in the combustion tube in the usual way. At temperatures easily ob-
