November, 1924
I N D U S T R I A L A N D ENGINEERING CHEiMIXTRY
the screw and lock nut seen in the center of Fig. 2. The soft iron core is thus moved to and from the moving magnet disk. The circuit breaker described will operate continuously in a 110-volt, A. C. line consuming 80 to 120 watts, with a breaking of the circuit at least once a second resulting in no sticking or fouling. I t was used successfully to operate a 500-watt electrical heater in a 110-volt line, where much less frequent contacts were made. Barely visible arcing of the mercuryplatinum contact of a toluene regulator resulted in the use of the device described. Duplicates of this apparatus made at the University of Michigan were tested through courtesy of A. L. Ferguson and L. 0. Case, using 220 volts in the high potential circuit with
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an energy consumption of approximately 100 watts. It was found impossible to prevent fouling of the silver contacts under these conditions without using a 0.025 microfarad condenser a t contacts M (Fig. 1). The apparatus described can be used in the vacuum tube type of thermoregulator control circuit described by D. J. and J. J. Beaver3 with some obvious modifications in wiring. Duplicates of this apparatus have been used in these laboratories during the past year with the best of results. The toluene-mercury thermoregulator described by Davis4 was used with excellent results. a 4
THISJOURNAL, is, 359 (1923). J. Am. Chem. Soc., 37, 1198 (1916).
Determination of Moisture in Wheat and Flour' Part I1 By Harry Snyder and Betty Sullivan RUSSELL-MILLER MILLINGCo., MIXNEAPOLIS, MINX.
Fluctuating flour moisture results were obtained by drying flour
mer sulfuric acid and phosphoric anhydride. Duplicate results on successioe days were followed by other and different sets of socalled constant weight losses. Drying flour ooer desiccating agents is no more accurate than other methods, because with each a contest goes on as to which, flour or desiccating agent, will possess the last trace of moisture. Desiccation offers no reliable way to standardizing othe,r methods, since there is always an uncertainty as to when ihe end point incident to drying is reached. Flour is highly hygroscopic and when dry a good desiccating agent, absorbing moisture f r o m reogents used f o r drying. When flour is dried above the boiling point of water there are certain points at which moisture losses are pronounced, indicating
N A. previous article2 are reported moisture results when flours are dried for 5 hours: (1) in a water oven heated to the temperature of boiling water, (2) in an electrically heated air oven at 105' C., and (3) in a vacuum oven a t 100' C. with a vacuum pressure of 500 mm. and upwards of mercur,y. A study was also made of various methods of drying over desiccating agents to determine if a method could be devised that would give the free moisture of flour without including other forms of moisture or causing chemical changes during drying that affect the accuracy of moisture results. It was desired to find such a method for standardizing other procedures of drying in which heat is employed, as well as heat and diminished air pressure, commonly known as vacuum drying. I n this article, Part 11, results are given when flours are dried in various ways over desiccating agents. The general technic, such as size of samples and drying dishes used, noted i n Part I, has been followed throughout the investigation. I n drying over sulfuric acid, unless otherwise stated, 15 and 20-cm. (6 and 8-inch) desiccators containing fresh charges of acid of 1.83 to 1.84 specific gravity were employed. The investigation was in progress several months and a study made of some of the more important factors which affect moisture determinations when desiccation and other methods of drying are employed. Not all the results are reported, as this seemed unnecessary when they harmonized with those of other investigators and with well-established principles.
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Received May 19,1924. THISJOURNAL, 16, 741 (1924).
chemical as well as physical changes, in which water of hydration oj the carbohydrates and proteins is inoolued. When flour is dried in an.y way dextrinization of the starch occurs with change in solubility proportional to the water of hydration expelled from the starch. Flour moisture results reported in standard works on foods are generally on a low dextrinization basis with partial dehydration of proteins. Diflerences qf from I to 3 per cent occur when different methods for determining flour moisture are used, in which trariahle amounts of wuter of hydration are remooed along w i f h the free or hygroscopic moisture. Due allowances f o r these differences i n moisture results should be made in commercial practices in which the weight and moisture content of flour are inoolved, as well as in research problems on wheat andflour.
DRYINGOVER SULFURIC ACID Tests were made to determine the effect which the quantity of acid used for desiccation had upon the moisture results. Portions of the same flour were dried in duplicate over different amounts of acid. I n Fig. 1, drying over 600 cc. of acid, Graph 2 , shows a maximum of 13.42 per cent of moisture, while drying over 200 cc. of acid, Graph 1,shows a maximum of 12.95 per cent followed by a drop to 12.53. In Fig. 2, the flour used contained 1 per cent less moisture than that used in Fig. 1. Here again the larger amount of acid caused more rapid drying a t first, but at the end of 10 days the difference in results obtained by the two quantities used was less appreciable. I n these tests where different amounts of acid are employed, if a new factor is introduced, such as a flour with a different moisture content, the conditions of desi ccation are changed as reflected in the graphs. The analyst has no way of anticipating the time required for complete desiccation, even with a definite amount of acid, except by resort to extended trials, and even then he may secure conflicting results. There are certain phenomzna, such as alternate gains and losses from day to day, that appear in many of the tests. These are discussed in later paragraphs. I n another test (Fig. 3) a flour (No. 3) dried over 100 cc. of acid yielded 9.5 per cent maximum moisture on the third day, and 9.85 per cent when dried over 500 cc. of acid. At the end of the seventh and eighth days each showed about 9.35 per cent. It is interesting to note that between the third and fourth days a loss occurred in each, while on the
