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rapid. T h e filtrate after neutralization is examined for sugars as before. A sample of milk was t a k e n which was found t o contain 4.64 per cent milk sugar. Four flasks of 2 5 0 cc. capacity were filled with I O O grams of t h e above milk a n d 5, I O , 2 0 a n d jo grams of pure cane sugar were added t o t h e m , respectively. Ten grams of each of t h e above prepared solutions were t a k e n in I O O cc. flasks, a n d made up t o I O O cc. F r o m each, 50 cc. were t a k e n , placed in four other 100cc. flasks, a n d coagulated with 2 per cent citric acid solution added drop b y drop, shaking all t h e while b y a r o t a t o r y motion. These were filtered a n d t h e filtrates made u p t o I O O cc. a n d t h e sugars were estimated as before. Percentage of lactose
Percentage of sucrose
r-.
Found
Calculated
Pound
Calculated
4.40 4.24 3.86 3.12
4.41 4.22 3.86 3.09
4.73 9.03 16.60 33.40
4.76 9.09 16.67 33.33
Some sweetened condensed milks were examined a n d t h e sugars estimated b y t h e above method, starting with a I O per cent solution. T h e following results were obtained: Brand
Ash proteid f a t lactose sucrose
1. Best skimmed condensed m i l k , , . . . . . . . . . . . 2. Nestle’s condensed milk, “ S e s t Brand” . . . . . 3. Milk-maid b r a n d . , . . . . . . . . . . . . . . . . . . . . . . . 4. Best skimmed condensed milk, cow and calf brand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vol. 6 , N o . 4
constant. After suffidient solvent has been added t o dissolve t h e whole of t h e soluble substance, further addition will dilute t h e solution without increasing t h e a m o u n t dissolved. I n t h e case of dextrin, however, no matter how small a n a m o u n t of water be employed, under no condition does t h e concentration of t h e solution obtained remain constant, while on t h e other h a n d t h e addition of further solvent never fails t o dissolve additional dextrin, although t h e use of no amount of water, however large, will dissolve t h e whole of t h e sample. This unexpected behavior seemed worthy of quantitative s t u d y , a n d a large number of dextrins were examined in t h e folloving way: Weighed samples were introduced & t h known a m o u n t s of water i n t o well stoppered bottles a n d shaken in a thermostat, After a certain time a p a r t of t h e mixture was whizzed in a centrifuge, and t h e water-soluble m a t t e r determined b y evaporation of a n aliquot p a r t of t h e solution. This was repeated until no further change in t h e concentration of the solution occurred, requiring a t no time over twenty-four hours. Characteristic results are shown graphically b y t h e following curves, t h e soluble frac-
Totai solids by evaporation
70.7 74.2 70.8
i0.2 74.8 io.1
i5,l
75.6
D
u >
I n conclusion, I h a r e much pleasure in expressing b y best t h a n k s t o A h . R. L. Jenks, Chemical Examiner for Customs a n d Excise, for his kindly allowing me t o analyze several samples of condensed milks. CUSTOMS A N D EXCISECHEMICAL LABORATORY CUSTOM HOUSE.CALCUTTA, INDIA
THE SOLUBILITY OF DEXTRIN’ By W. K. LEWIS Received December 26, 1913
I n a n a t t e m p t t o find a rapid method of determining t h e proportion of dextrin soluble in cold water, t h e a u t h o r some time ago t r e a t e d weighed dextrin samples with known amounts of water in t h e tubes of a centrifuge, a n d after thorough agitation separated t h e suspended insoluble m a t t e r b y whizzing. The soluble portion was determined b y t h e evaporation of a n aliq u o t p a r t of t h e clear solution. T h e ratio of water t o sample was varied t o insure sufficient solvent so t h a t t h e solution should not be s a t u r a t e d with respect t o a n y of t h e soluble constituents of t h e original dextrin. It was surprising t o find t h a t t h e soluble fraction increased rapidly with dilution. If a physical mixture of a soluble a n d a n insoluble substance b e treated with increasing a m o u n t s of a solvent, we shall first obtain a s a t u r a t e d solution of t h e solute a t t h e temperature employed, t h e excess solute remaining undissolved. During t h i s stage t h e concentration of t h e solution obtained mill remain 1 All d a t a quoted in this article are taken from a thesis by C. W.Hobson, submitted in partlal fulfilment of the requirements for the S B. degree a t the Massachusetts Institute of Technology.
CONCENTRATION
-
G R A M S PER L I T E R
tion of t h e dextrins being plotted as ordinates, abscissae being t h e concentration of t h e solutions obt ained. With t h e idea in mind t h a t t h e insoluble portion of t h e dextrins might serve as a body on which t h e soluble portion could be adsorbed, these quantitative results were studied in t h e following way: Call t h e fraction of t h e dextrin insoluble in water, however great in a m o u n t . a t t h e temperature in question, I -~i. It follows t h a t a n indefinitely large a m o u n t of water will dissolve t h e fraction A . The fraction actually dissolved, as determined b y experiment, is designated b y x . T h e fraction soluble in water infinite in a m o u n t , b u t retained on t h e insoluble portion under t h e conditions i n question, is A - x. T h e concentration of t h e solution, expressed in a n y suitable way, call c. If t h e
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Apr., 1 9 1 4
T H E J O C'R S -4 L 0F I AVD C'S T RI A L il S D E -VGI *\E ' E RI N G C H E M I S T R Y
soluble portion unaffected b y t h e water be adsorbed o n t h e insoluble residue, one would expect t h e relationship t o be represented b y t h e adsorption equation, which in this case will be A - x = Kc', '. Taking t h e logarithms of both sides: log (A - x) = log k 1 , ' f Z log c. This requires t h a t t h e logarithm of t h e soluble portion remaining undissolved under t h e conditions of t h e experiment shall be a straight line function of t h e logarithm of t h e concentration of t h e solution. It is of course theoretically possible t o determine t h e insoluble residue b y t r e a t m e n t of t h e dextrin with a n indefinitely large a m o u n t of water. This is,
+
insoluble fraction, b u t t h e t w o constants of the adk a n d fz-are highly sorption equation-namely, characteristic of t h e dextrin employed, a n d in t h e opinion of t h e author offer a better means of distinguishing between samples of dextrins t h a n a n y other method hitherto suggested. For t h e purpose of testing dextrins b y this method, t h e procedure t o be employed is t o t r e a t weighed samples of t h e dextrin with known amounts of water in a thermostat for approximately twenty-four hours, a n d determine t h e water soluble portion b y evaporation of a n aliquot sample of t h e liquid after whizzing i n a centrifuge. T h e easiest method of determining t h e constants of t h e dextrin will t h e n be t o assume values for t h e total soluble fraction A . a n d t o plot t h e logarithm of A - x against t h e experimental values of t h e logarithm of c until a chosen value of results in a straight line. This value of A is t h e soluble portion, , t h e intercept of this t h e slope of this line is ~ / n and line is t h e logarithm of K . For t h e dextrins plotted, these constants are tabulated below: Substance Yellow dextrin.. . , . , , , . , . White dextrin , . . . , , , , . , . . . . LVhite dextrin. . . . . , , . . . . . . , , Imported potato g u m . , . , , , , , Thin corn gum , . . , , , , , . , ,
LOG
C O N C E N T RATION
hom*-ever, difficult, a n d i t is wiser t o determine A in t h e following w a y : If there exist a n y value of A which mill make t h e logarithm of A - x a straight line function of t h e logarithm of c , for all values of c however small, t h e n this value of A is a most probable one for t h e soluble fraction of t h e dextrin: T h e d a t a of t h e previous plot were tested b y plotting log, (A - x) as ordinates against log c as abscissae, different values of A being chosen. i t was found t h a t b y varying t h e v a ue of -1 t h e curve could be made concave either u p or down. a n d t h a t a suitable intermediate value of -1 would in all cases straighten out the plot. These plots are shown in t h e above diagram. I t is found from these results t h a t a t z j o C.. t h e assumption of t h e presence in t h e dextrin of a residue insoluble in water, upon which a fraction of t h e soluble portion is adsorbed, offers a quantitative explanation of t h e behavior of t h e dextrin on t r e a t m e n t with water. I t is desired t o point out t h a t not only this
309
25' 25' 18' 25'
25'
A
1'n
0.995 0.935 0.800 0.920 0.400
0.272 0.250 0.240 0.168
k 17.20 7.18 9.62 3.81 6.05
0.100
As shown in t h e first plots, one "Partial Dextrin" v a s found, t h e solubility of which is independent of the a m o u n t of water used, 2 2 per cent being dissolved in all cases. This sample is probably made b y mixing a highly hydrolyzed product (practically a grape sugar) with untreated starch, adsorption being absent o x i n g t o t h e low molecular weight of t h e soluble portion. I t is not wished t o have it understood t h a t t h e a u t h o r considers t h e results here presented as proof t h a t adsorption is necessarily t h e explanation of t h e phenomena observed. Dextrins are unquestionably highly complex bodies, 1 t h e Fig / components of which vary in solubility, a n d it is easily possible t h a t t h e behavior on treatment with SO/U /loo increasing amounts of water is due t o t h e solution of increasingly insoluble components.l Such a hyLeJi..r pothesis, however, it is impossible f'deirrmn) Whfe /eyer t o express in mathematical form, /s/.rc*/ suggestion n-hich is B h r i i q v r r /
