JUNE 15, 1940
201
50
317
ANALYTICAL EDITION
100
150
200
250
300
350
I
SECONDS
FIGCRE13. RATE OF SOLTJTION OF PREPASTED COLD WATER-SOLUBLE STARCH
Thus the calculation yields 43 per cent of tapioca at 80” C. and 45 per cent at 89.5’ C., while at 66” C. 40 per cent of corn IS indicated. The comparison curve of a 40 per cent corn, 40 per cent tapioca, and 20 per cent wheat mixture shows the correctness of conclusions in the general closeness of the two curves. Such analysis, however, may be used only where the pasting, as shown in Figure 11, results in general swelling of the starch grains. The picture is of a textile printing paste showing swollen pasted starch, which is used as the thickening agent for carrying the dark particles of dyes.
Where the pasting involves fragmentation of the starch particle, as with dextrins which split off ringlike fragments, the relationship of solids to light transmission is evidently different from that shown by unpasted starch suspensions. Thus in Figure 12, which shows the effects of progressive dextrinization of white potato starch, three starches of 20 per cent solubles are shown. The true dextrin of 20 per cent solubles is easily located. The starch made b y mixing a 30 per cent solubles with raw starch shows the presence of the raw starch in its curve location. However, it is apparent that this curve could not be used satisfactorily to calculate the composition. The third 20 per cent soluldes dextrin was eridently a mixture of at least two dextrins and a small amount of raw starch. Obviously gums, proteins, oils, or other admixtures not giving clear solutions affect the curves and show their presence. Figure 13 offers rate of solution curves for a prepasted cold water-soluble starch and for a starch which was evidently the same,
Literature Cited (1) Alsberg, C. L., and Rask, 0. S.,Cereal Chem., 1 , 107-15 (1924). (2) Cook, D. H., and Axtmayer, J. H., ISD. ENG.CHEM.,Anal. Ed., 9, 226-8 (1937). (3) Lane, J. H., and Eynon, L., “Starch Chemistry”, pp. 92-3, Cambridge, England, W. Heffer & Sons, Ltd., 1924. (4) Sjostrom, R . L., IND.EX. CHEM.,28, 63 (1936). PRESEKTED before the Division of Sugar Chemistry a n d Technology a t the 9Sth Rleeting of the American Chemical Society, Boston, M a s s .
Simple Hot Filtrations and Crystallizations JOHIV W. DAWSON AND WILLIAM M. DEHN University of Washington, Seattle, Wash.
A
GREAT inconvenience in filtering hot saturated solutions is crystallization in the paper and in the stem of the
funnel. Hot-water funnels are not always available or may be fire hazards. The depicted forms, built from stock apparatus, employ truncated funnels and filter papers pending therethrough. The beakers are ordinary or are indented to support the funnels. The funnel in the large beaker rests on an inverted cutoff widemouthed bottle. The evaporating dish may contain water or ice. The glass cooling bulb is a modification of Conant’s apparatus ( I ) , carrying warty lumps on its bottom to distribute the condensed solvent over the solid contained in the funnel. Some of the solvent is placed in the beaker and heated t o boiling for the time necessary to heat the entire apparatus. The boiling solution, contained in another beaker, is then poured in and heating is continued until filtering is complete or until the boiling solvent has supplied sufficient vapor to dissolve all material in the filter paper. The large beaker is especially useful when water is the solvent. The bulb condenser is useful with difficultly soluble solids, since i t is practically automatic. This apparatus has a decided advantage over that of Tanner (2, S), in that fresh solvent is continually in contact with the material being filtered.
Literature Cited (1) Conant, J. B., “Organic Synthesis”. Vol. 11. p. 49, New York, John Wiley & Sons, 1922. (2) Stoltenberg, Chem.-Ztg., 33, 759 (1909). (3) Tanner, H. G., IND. EXG.CHEM.,Anal. Ed., 4, 397 (1932).
