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ANALYTICAL EDITION
PROCEDURE-Measure 100 cc. of extract into a long-necked flask of the type described above. (A smaller sample may be used if more than 0.05 per cent pyrethrin I is known to be present.) Add 5 cc. alcoholic soda solution and reflux for 11/, to 2 hours, the bulb of the flask being immersed in a beaker of hot water. Shake occasionally. Remove from the beaker and pour off as much kerosene as can be decanted without disturbing the alcohol layer into another similar flask which contains a second 5 cc. portion of alcoholic soda. Reflux as before, and when completed, pour off the kerosene layer, rejecting it. A few cubic centimeters of kerosene will remain in each flask. Add to the second flask 11 cc. 1N sulfuric acid, shake, and transfer to the first flask. Rinse the second flask with two 25-cc. portions of petroleum ether, and after transferring these washings to the first flask, confirm its acidity with phenolphthalein. Distil in a current of steam, using a long condenser cooled with ice water. Do not apply a flame to the distillation flask until all the petroleum ether has been distilled. Collect the petroleum ether and 50 cc. of water in a separatory funnel, then continue the distillation until an additional 50 cc. of distillate has been collected. Keep the volume low in the distillation flask, but do not allow it to go dry. The titration is carried out in an Erlenmeyer flask to which has been added about 20 cc. carbon dioxidefree water, a few cubic centimeters of ethyl alcohol, and 1 cc. of phenolphthalein indicator. Add to this enough 0.02 N sodium hydroxide to give a definite pink color, usually one to two drops will be sufficient. Shake the contents of the separatory funnel vigorously and add the water layer to the second 50 cc. of distillate. Wash the petroleum ether layer
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with about 20 cc. of water, then add it to the titration flask. Titrate to a definite pink, shaking well and allowing the layers to separate after each addition. Extract the combined distillates with a second 50-cc. portion of petroleum ether, and add this to the titration flask. Continue the addition of caustic until the pink color is the same as it was originally. A blank determination should be run, using 100 cc. of kerosene, and the proper deduction should be made from each determination. This will usually be about 0.3 cc. CALCULATIONS-From the molecular weight of 330, we get the relation, 1cc. 0.02 N caustic = 0.0066 gram pyrethrinI. Summary
The copper reduction and the short acid methods for determining active constituents in pyrethrum flowers are compared, and several samples of Dalmatian and California flowers run by the short acid method. A series of experiments on the adaptation of the short acid method to a kerosene extract of pyrethrum are discussed. A method for the quantitative estimation of pyrethrin I in a kerosene extract is described, along with a table showing pyrethrin I content of spent flowers and the extracts from these flowers. Literature Cited J . Am. C h e w Soc., 51, 3054 (1929); 62, 680, 684 (1930). (2) Gnadinger and Corl, Ibid., 62, 3300 (1930). (3) Staudinger and Harder, Ann. acad. sci. Fennicae, [ A ] 29, No. 18 (1927). (4) Staudinger and Ruzicka, Helu. Chim. Acto, 7,177,450 (1924). (5) Tattersfield and Hobson, J . AEr. Sci., 19, 433 (1929). (6) Tattersfield, Hobson, and Gimingham, Ibid., 19, 266 (1929).
(1) Gnadinger and Corl,
A Modified Balance for Approximate and Quick Weighing’ E. Karrer B. F. GOODRXCA Co., AKRON,OHIO
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ANY cases arise when the time required to make a weighing must be kept at a minimum either because the weighings are approximate and large expenditure of time is unwarranted or because many things of the same kind are to be weighed. The economics of mass production demand that as little time as possible be spent upon each weighing. There is a very simple and inexpensive method for accomplishing this by modifying an ordinary beam balance as shown in Figure l. A spring, S,is mounted directly under the beam, H, in which two adjustable studs, A , are inserted. These studs barely make contact with the spring, X, in the balanced condition. For example, the distance between the hardened ends of the studs and the spring may be 0.01 inch (0.25 mm.). The index, B, is lengthened and its position read by a scale, C. I n making a weighing the scale pan, G, is depressed to the stop, E, and then is released quickly and carefully. If the weights on the two scale pans are equal the index will be deflected on its first swing to a point that may be marked zero on the scale, but if the weight on the scale pan, F , is slightly more than that on G, the index will not travel to that point. The distance traveled depends upon the difference in the weights on the pans. The modification described is best suited for comparing one article 1 Received September 20, 1930. Presented before the Division of Rubber Chemistry at the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12,1930.
with another which is intended to be of the same weight and which is to be trimmed or adjusted to a given weight within certain tolerances. I n such a case the standard article (“weigh-by”) may be placed upon the pan F, and others, placed on pan G, be compared with this.
Figure 1-Balance Modi5ed for Indicating Offweight on First Deflection
The scale C may be put in units of weight, of length, or of volume. For example, for comparison and control of pieces cut from ribbon or tubed stock, the wale C may be graduated in centimeters, indicating the length which must be cut from, or added to the piece in order to make its weight within tolerance limits equal to the weight of the standard. For
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January 15, 1931
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guessed at, one must observe theoretically a t least 11/z oscillations-making the time required approximately 3 seconds, but a much longer time is involved in actual practice, as just indicated. Comparison with Unmodified Balance
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2
I _____ _ _ _ _ _ :4---_---- ----0:s .o O!i!
0
LOAD
Figure 2-Time
0'0
I
1.2
ON PANS tN KLLOORAP16
and Number of Oscillations before Coming t o Rest
general purposes, the scale C graduated in terms of grams is more useful. It may even be graduated in terms of spoonfuls in case the materials being weighed are being meted out by approximate volumes, or it may indicate the number of cuts of a given size that are required to reduce the weight to within specified tolerances. I n a balance so equipped, it was found that an article could be laid upon the pan, the beam deflected, and the scale indicating the underweight or overweight read off in 2 seconds. By the ordinary method of weighing, this process consumed at least 21/2 seconds when the balances are read on the gothat is, when the state of balance was merely judged as to overweight or underweight by noting several deflections of the balance. An experienced operator can do this with fair accuracy a t high speed. However, when the weight is obtained in 2 seconds, by the modified balance, exact information as to overweight and underweight is a t hand, while when obtained by the ordinary method just mentioned, the overweight or underweight is only guessed at, so that at least one other trial on the balance is necessitated. This increases the time for one adjustment to at least 5 seconds. 38 %--
25%
I
.-
Figure 3-Distribution of Weight among Rubber Blocks before and after Adjustment with Balance I t was modified to indicate offweight quickly.
Figure 2 shows how certain characteristics of a balance change when i t is equipped with a spring for quick weighing. From these curves a comparison may be made for different modes of weighing. I n the method now discussed for the new balance, a weighing is made on the first half-oscillation of the index. The time (approximately 1 second) of the first half-oscillation is constant over a large range of loads (curve 1). When the condition of the balances is merely
To compare a balance modified for quick weighing with one unmodified and used in the ordinary way by estimation of the state of balance, a number of strips of rubber used in a routine process in the factory were weighed and adjusted by the two methods. The results are indicated in Figure 3, where the distribution of the samples according to weight is indicated by full columns for the balance equipped with the spring and used in the first deflection manner and by light columns for the customary method. Overweight and underweight are indicated on the abscissa in terms of centimeters of length. By the new method the number of products which are exact is over 50 per cent greater than the number by the usual method. I n general, the distribution is changed in a very favorable manner-that is, the number showing small over- or underweight is generally much larger by the new
50t
Underweight
1
!I
I
O v e r weight
Figure 4-Distribution Curves for Overweighted Blocks before and atter Adjustment with Ordinary and Modified Balances
method. The number which lie in the region of large underweight and large overweight are very much greater by the customary method than by the first deflection method with the modified balance. Further striking data are shown in Figure 4. I n this case the distribution according to weight of rubber blocks as received is shown by curve A . After weighing and trimming by the usual method the distribution for several thousand blocks is represented by curve B. When the modified balance is used in the first deflection manner, curve C is obtained. The number of blocks weighing within 1 per cent of the standards has been greatly increased in the last case. There are practically no blocks differing by as much as 2 per cent from the standard. These weighings were made by one who had had much experience with these blocks in the factory. She had had no experience with the new method of weighing. When the things to be checked by weighing have a cross section not favorable for adjustment by cutting off given lengths, then another method is to make certain that the blocks of material as delivered for checking are 04an average slightly underweight. Then for adjustment, some small quantity of the material of standard shape may be added
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I
1 B A(tar single rueighing I with the rnodilied Bolonce I 4 I I
4 /A I
t?S receivad
L 1
5 %
Under weight Figure 5-Distribution Curves after Adjustment with Modified Balance of Underweight Blocks
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to bring the weight up to the comparison standard. The balance scale is now in terms of length, say of the stock to be added. An illustration of this is given in Figure 5, where the blocks as delivered for checking are represented by the distribution curve A. The resultant distribution after the adjustment has been made with a single weighing is represented by curve B. The “weigh-by” in the case of Figures 4 and 5 was 1.7 kg. The variation in weight of blocks as delivered was so great that two springs were used t o extend the offweight scale. It is to be remembered that in making these weighings only a single laying upon the pan is necessitated by the modified balance with the single deflection method, whereas in the usual method, a t least two, sometimes three or four weighing operations are required before the sample has been brought within limits. Not only is the distribution curve more favorable with the former method from the standpoint of elimination of waste, but it also consumes considerably less time. To make the weighings represented in Figure 4 required at least 10 per cent less time using the modified balance in the first deflection manner than when the customary method is employed. On another occasion 6 blocks per minute were adjusted by the new as compared with 5.04 by the customary method, or 19 per cent faster. If a comparison be made on the basis of the time required to bring about the same distribution, a much neater difference is brought out. I
Apparatus for Continuous Leaching with Suction’ J. F. Fudge TEXASAQRICULTURAL EXPERIMENT STATION, COLLEGE STATION, TEXAS
ANY laboratory methods require the continued leaching or washing of material. The addition of the leaching solution may become very tedious and time-consuming if a wash bottle or aspirator bottle be used. Schollenberger and Dreibelbis (1) describe an apparatus for continuous leaching. It is not, however, adopted to use with suction, and hence is unsuited to many laboratory operations. For example, in the determination of the base exchange capacity of a soil, as conducted in this laboratory, 10 grams of soil in a 35-00. Gooch crucible are leached with 250 ml. of a neutral, normal solution of ammonium acetate. The excess ammonium acetate is then washed out with 95 per cent alcohol until the leachate gives no test with Nessler’s solution. Suction is applied in order to reduce the time required for leaching and washing. Many soils leach very slowly, and without some self-operating apparatus a great deal of time may be lost in adding the leaching solution. For this reason, a number of different arrangements of apparatus were tried and the one described below finally selected. This has been found very satisfactory. The sizes and dimensions of the materials used are those adapted to the work described above. They may, of course, be varied a t will to meet the requirements of other work. The diagram gives all the essential characteristics of the apparatus. A few points should, however, be noted. The glass tubes are flush with the bottom of the stopper allowing
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Received October 11, 1930. Technical Article 127 of the Texas Agricultural Experiment Station.
for the complete removal of the measured volume of solution. The rubber tubing enables slight adjustment of the height of the glass tips. Tip B is drawn to a small hole in order to prevent splashing of the soil in the crucible. The tip of tip B should be a t least 1/4 inch below the tip of tip A. This difference is necessary in order to keep the solution flowing from tip B when tip A is in the air; if A and B are a t the same height, both tubes fill up with solution and the flow stops. The entire a p p a r a t u s is inverted after filling with the solution, and supported by a wooden s u p p o r t , with the b o t t o m of both tips w i t h i n a n d below t h e edge of t h e crucible. Figure 1-Diagram of Apparatus v
Literature Cited
1
(1) Schollenberger and Dreibelbis, Soil Science, 80, 166 (1930).
