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INDUSTRIAL AND ENGINEEBJNG CHEMISTRY
to know its boiling point. This is, however, not'the same as the initial boiling point in a regular Engler distillation where the thermometer is in the neck of the flask, but rather the true initial boiling point with the thermometer in the liquid, which is generally from 30" to 60" F. higher. The curves may similarly be used to determine the vacuum or the amount of steam required to bring a given fraction over below a certain temperature, but here again the boiling point a t atmospheric pressure should be determined with the thermometer in the liquid a t the time when the desired cut has been distilled off. Incidentally, it should be noted that the vapor pressure curve of unsaturated and cyclic hydrocarbons checks up very closely with those for saturated hydrocarbons of similar boiling points. (The curves cannot, however, be applied with equal accuracy to alcohols, esters, or other organic compounds containing elements besides carbon and hydrogen.) In any such interpolations the vapor pressure and other curves should be considered as representing a family of essentially parallel curves, and it is not necessary to follow any particular line but rather to determine the atmospheric pressure boiling point of the cut exactly and assume a line passing through this point which will fit in with the family of curves. In the case of heats of vaporization the figure usually desired is the heat of vapori~ationof an entire cut. For this purpose the average boiling point of the same should be obtained by averaging the temperatures a t all points from initial to the maximum. In this case again the thermometer
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should be in the liquid, but the error is not large if the ordinary vapor temperature results are used, since the heat of vaporization does not change very rapidly with the boiling point. Reference should be made to Fig. 4 for results a t atmospheric pressure, or to Fig. 3 for results at other pressures, after determining what hydrocarbon most nearly corresponds to the average boiling point of the cut in question a t atmospheric pressure. I n the case of liquid densities the preferable procedure is to make comparisons between the refinery cut and that pure hydrocarbon which has the same density a t the same temperature, regardless of whether or not its boiling point checks up. In the case of vapor densities it is probably best to make comparisons on the basis of hydrocarbons of similar molecular weights. These data will not apply to aromatic hydrocarbons a t high pressures, since their critical points are much higher than those of the paraffin hydrocarbons. In the case of the critical data there are not sufficient data to make sure what is the best, method of applying the results to refinery cuts containing unsaturated or cyclic hydrocarbons, but fortunately there is seldom need for critical data in refinery operations and a rough comparison with pure compounds of similar boiling points would probably be the best approximation for petroleum hydrocarbons. The specijic heat data have already been obtained on refinery cuts, but there is no definite data as to how they vary with degree of unsaturation, etc.
The Rates of Fermentation of Sugars by the Propionic Organism' By E. 0.Whittier, J. M.Sherman, and W.R. Albus DAIRYDIVISION. U. S. DEPARTMENT OF AGRICULTURE, WASHINGTON, D . C.
REVIOUS work by Sherman and his associates2 on the propionic fermentation has dealt with its bacteriological and chemical features, especially in their bearing on the use of the propionic organism in the manufacture of Swiss cheese and in the production of propionic acid in quantity from whey. Among the points established was the fact that the organism ferments not only lactose, but also a number of other substances, chiefly organic salts and sugars. The chief objection to the use of the process for fermentation of the lactose in whey to propionic and acetic acids is the long period of incubation required-approximately 2 weeks for an 85 per cent yield under most favorable conditions. Since there are, in addition to whey, other cheap sources of carbohydrates, it was considered worth while to compare the speeds of the propionic fermentation of the most common cheap sugars. Galactose was included, partly because of theoretical reasons arising from its relationship to lactose, and partly because of the possibility of its becoming available in large quantities in the near future. Eight-ounce bottles were prepared, containing 5 grams of sugar, 5 grams of precipitated calcium carbonate, and 1 gram of dried yeast, in 100 cc. of water. After sterilization each bottle was inoculated with 1 cc. of a culture of Bacterium acidi-propionici ( d ) and a loopful of a culture of 1 Received September 26, 1923. *Sherman and Shaw, J . Gcn. Physiol., 3, 657 (1921); Sherman, J . BUG:.,6, 879 (1921); Sherman and Shaw, Sci. Proc. SOC.A m . Bacteriologists, AbsLracIs Bad.. 6 , 16 (1922); Shaw and Sherman, J . DairvSn'., 6,303 (1923); Sherman and Shaw, J . B i d . Chcm., 66, 695 (1923); Whittier and Sherman, T E I ~JOURNAL, 15, 729 (1923).
Lactobacillus casei, and incubated a t 30' C. for 16 days. The volatile acids produced were distilled off and determined by the method of Duclaux. The results are shown in Table I. TABLEI-RELATIVE SPEEDOF FERMENTATION OF SEVERAL SUGARSBY THE PROPIONIC ORGANISM PER CENT OF TAEORETICAL YIELD GRAMS O F ACIDPRODUCED Propionic Acetic Propionic Acetic SUGAR 47.3 34.8 1.2967 0,3863 Lactose 39.9 0 4430 52.9 Galactose 1.4493 .56,0 40.8 0.4528 GIu cose 1.5351 57.6 42.8 0.5008 Sucrose 1,6638 77.7 71.4 0.7928 Maltose 2.1290
Variations wider than expected were obtained in the amounts of volatile acid produced in the same period from the different sugars. Since the time of incubation was chosen so that none of the fermentations was complete, the amounts of volatile acids found should be a fairly accurate measure of the relative rates of fermentation. This statement may be objected to on the basis that the per cent of theory yield is the strictly scientific measure. However, the choice of either basis will give identical ratios in the cases of the sugars used except in those where sucrose is concerned. Glucose, galactose, and sucrose are fermented by the propionic organism somewhat more rapidly than lactose; weight for weight, sucrose has an advantage which does not appear when the theoretical basis is chosen; maltose is fermented about 60 per cent faster than lactose, and about 30 per cent faster than the other sugars. The relative advantage of these sugars in the commercial production of propionic acid would depend, of course, on relative cost and availability as well as the speed of fermentation.
