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Vol. 15, No. 12
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
compared with a fraction in the middle of the series (C, 87.58;
H, 12.45), viscosity of the first oil a t 50" C. 317 seconds and of the second oil 2005 seconds, water equivalent 2.8 seconds. The carboxyl oil dissolved out from Mecca 1-D fraction, specific gravity 1.0105, gave by combustion 86.70 per cent C, and 12.41 per cent H, with a difference of 0.89 per cent for 0 2 . The viscosity of this oil was 468 seconds as compared with the hydrocarbon C120H220,specific gravity 0.9171 a t the lower end of the same series, viscosity 1073 seconds a t 50" C., water equivalent 2.8 seconds. It would be of interest to isolate larger quantities of these oils and ascertain their composition. UNSATURATION AS SnowN BY IODINE NUMBERS Of the two forms of unsaturation, open chain and the ring, evidently only the latter applies to the lubricant hydrocarbons and it has received much attention with respect to this condition as shown by the iodine numbers. Iodine reacts indiscriminately on the D and H hydrocarbons without showing any consistent relation or differences, but with results much like those observed in distillates. Trial of the Johansen method that appears to reveal what has been regarded as
addition is really substitution, not only disproved addition, but gave negative numbers to the extent of two to four units.
FORMALITE REACTION The D hydrocarbons described in this paper do not enter into this reaction as applied by the Marcusson method frequently quoted in works on lubrication, and the H hydrocarbons of the Texas and Russian oils give variable mixtures with an indefinite composition. The Rosenbury fraction 3-H, specific gravity 0.8512, gave after the reaction, 0.8827; and the Russian fraction 4-0, specific gravity 0.9262, after the reaction, 0.9291. I n no case cou€d the reaction proceed unless the resulting increase in temperature was unchecked. No naphthene, C,Hh, lubricant hydrocarbons have appeared, and contrary to the statement of Marcusson, the hydrocarbons from American petroleum have shown a superiority in lubricant quality over those from the Russian oil.
Acx NOWLEDGME NT The writer wishes to acknowledge the efficient aid which he has received in this work from his assistants, R. C. Knapp and George Grossman.
T h e Value of Sweet Potato Flour in Bread-Making' By H.C. Gore
'
BUREAUOF CHEMISTRY,WASHINGTON, D. C.
I
T WAS recently shown2 that two widely grown commercial varieties of sweet potatoes, Nancy Hall and Porto Rico, are rich in diastase and that they retain their diastatic power when sliced, dried, and ground into flour. The diastatic power ranges from 200 to 500 Lintner. That in the southern sweet potato we have a source of diastase capable of competing with the cereal sources of this important enzyme is shown from a study of the economics of sweet potato production. The present cost of growing sweet potatoes on southern farms is shown by Haskel13to range from 22 cents per bushel upward, depending on the yields, the higher yields (160 bushels per acre) being produced a t the lower unit cost. Sweet potatoes are a sure crop, respond well to fertilizers, and their cultivation is well understood. The entire crop or any portion of it can be used as raw material for the production of sweet potato flour. I n a normal season about 40 per cent of the crop overgrows-that is, the roots become so large (greater than 3.5 inches in diameter) that they are not in demand for table use. They are, however, acceptable for technical uses. I n preparing sweet potato flour the process required is very simple. It is not necessary to peel the potatoes; they should, however, be washed in order to remove adhering soil. They are then sliced and dried. I n drying, an u p draft drier has been found to give satisfactory results. The temperature employed should not exceed 50" C. The yield is one-third the weight of the potatoes taken. Sweet potato flour imparts but little flavor to the mash. It does not liquefy starch so rapidly as barley malt. It has, however, much greater saccharifying power. Its uses in 1
Presented before the Division of Agricultural and Food Chemistry
at the 05th Meeting of the American Chemical Society, New Haven, Conn.,
April 2 to 7, 1923. * J . B i d . Chem., 44, 19 (1920). 8 U. S. Deal. Agr., Bull. 648.
industry remain to be worked out. The most interesting development which has occurred thus far is the discovery of the fact that sweet potato flour can be used as a bread impr~ver.~ A large number of experiments were run in which a series of mixtures with varying percentages of sweet potato flour with hard wheat flour was tested. The different percentages of sweet potato flour used were based on the weight of flour taken. The baking tests were made by the straight dough method, with the following formula: GRAMS PER BATCH Flour Salt Sugar Yeast Water
460
7
16 10
Sufficient to produce a dough of proper consistency
The sweet potato flour was mixed with the liquid ingredients before the wheat flour was added. Before panning, 170 grams of dough were removed for expansion tests, the remainder being panned for baking. It was found that a substantial increase in volume occurred when sweet potato flour was used. One and one-half per cent of sweet potato flour appeared to give the best results. I n one test, which may be considered as typical, the volume of the control loaf was 2250 cc., whereas that of the loaf prepared from the mixture containing 1.5 per cent sweet potato flour was 2425 cc. The texture of the bread and its color and flavor remained fully up to the standard. These results have been confirmed by independent tests made in three commercial baking laboratories. There is, therefore, no doubt of the fact that sweet potato flour does give a substantial increase in volume when used as a bread improver. 4 The baking tests herein reported were made by I,. H. Bailey, of the Bureau of Chemistry, and Miss R. Leone Rutledge, formerly of the Bureau of Chemistry.
