INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 7, NO. 5
voltage variations. It is adaptable to a variety of uses where low voltages are t o be measured with a minimum current drain.
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Literature Cited
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(1) Dubridge, Phys. Rev., 37, 392 (1931).
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Dubridge and Brown, Rev. Sci. Instruments, 4, 532 (1933). Furman, IND.ENG.CHEM.,Anal. Ed., 2, 213 (1930). Goode, J . Am. Chem. Soc., 44, 26 (1922). Harnwell and VanVoorhis, Rev.Sci. Instruments, 5, 224 (1934). Nottingham, J. Franklin Inst., 209, 287 (1930). (7) Soller, Rev. Sci. Instruments, 3, 416 (1932). (8) Turner, Ibid., 4, 665 (1933). (9) Turner and Sieglin, Ibid., 4, 429 (1933). (10) Wynn-Williams, Phil. Mag.,[7] 6, 324 (1928). (2) (3) (4) (5) (6)
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RECEIVED June 8, 1936. Presented before the Division of Physical and Inorganic Chemistry, Symposium on Recent Advances in Microchemical Analysis, at the 89th Meeting of the American Chemical Society, New York, N. Y., April 22 to 26, 1935, under the title “Use of Multi-Purpose Radio Tubes in Analytical Chemistry.”
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A Simple Rotating Ball Mill
MILLIVOLTS IRsm
FIGURE 3. SENSITIVITY CURVE line. The same operation should now be repeated with the other section of the tube. For very high stability readjustment of R4 may now be necessary. The operating stability may be judged by reconnecting the microammeter and noting the change in its reading with line voltage. Improvement in stability can often be obtained by further critical readjustment of Rsand R4 until maximum stability is indicated by the microammeter. Once this adjustment is completed, no further changes are required until replacement of the tube is made. Before using the instrument, the microammeter should be made to read zero, with zero input, by adjusting resistors R7 and Rs. This compensates for differences in the plate impedances of the two sections of the tube.
ARTHUR H. FURNSTAL Division of Plant Nutrition, University of California, Berkeley, Calif.
OR certain investigations it was necessary t o design a F s i m p l e , compact, efficient, and portable ball mill. Several modifications were tried, of which the mill described below has proved the most satisfactory. It consists of two horizontal rotating shafts upon which is placed a cylindrical container made of steel or glass, holding the material t o be pulverized, and rotated by the revolving shafts. The mill .5.4-
I
The switching arrangement permits the voltmeter t o be used in the following ways: 1. SI open, S,to the right, SSto the left, S, closed. The instrument is now a high resistance voltmeter with a range 0 to 1 volt. 2. SIopen, .Szto the right, 8s to the left, 8,open. These operations disconnect the grid leak and make the instrument available for electrometric titrations and other potential measurements where low current drain is important. Under these conditions the maximum current will be 10-8 ampere. 3. SI closed, SI to the left, S a to the right, S, any position. Under these conditions the instrument serves .as a galvanometer which may be used in the usual Poggendorf method. When balanced, the meter will show equal deflections when SZ is moved from left to right. When the external electrode resistance is high, SI should be left open. It should be noted that the second section of S,serves to disconnect the microammeter during the transition of the first section of SZ,thus preventing the meter from reading off-scale during the interval the grid is open.
Stability and Sensitivity The degree of stability that is obtained is shown in Figure 2. The variation produced by ordinary changes in line-voltage will produce imperceptible changes on the 0-200 microammeter recommended. The sensitivity curve, Figure 3, shows that the microammeter readings are linear with input voltage and that a 0-200 microammeter provides ample range for all electrometric titrations.
Summary A self-contained vacuum-tube voltmeter is described which is capable of operating on alternating and direct current lines and designed to minimize the effects of line-
FIGURE 1. DIAGRAM Upper left, cross section of container. Upper right, end view of container. Lower, top view of rotating shaft assembly.
may be easily constructed a t a small cost in the average laboratory. Many substances, such as soils, pure minerals, plant materials, bacteria, glass, etc., have been ground in this mill. Figure 1 gives a general idea of the principles of this mill The shafts are steel, 0.5 inch by 3 feet or longer and are 3.25 inches apart from the center of each shaft. The bearings are common, split pillow blocks with a hole drilled through the top for oiling purposes. The shafts between the bearings are covered with ordinary rubber tubing which is slipped on with the aid of powdered talc. The rubber tubing quiets the operation and gives better traction to the mill. There is a 2-inch pulley a t one end of each shaft, connected by a 0.25-inch round belt. The other end of one shaft has a larger pulley, approximately 4 to 6 inches in diameter, connected to an electric motor of about 0.25 horsepower by an endless belt.
SEPTEMBER 15, 1935
AWALYTICAL EDITION
The grinding chamber is made of a steel tube 3.25 inches in diameter by 3.75 inches long, machined on the inside and ends, as illustrated. The ends are steel plates 3.5 inches in diameter bv 0.25 inch thick, turned and grooved t o fit the chamber. A hble was drilled and threaded in the center of one plate to fit a 0.375- by 4.5-inch steel rod threaded at both ends. The center of the other plate was drilled with a slightly larger hole. A nut was screwed on the outside of the rod, which runs through the center of the chamber, tightening the two plates against the turned steel tube. The plates and steel tube should be machined carefully; otherwise the mill will not retain finely divided material. These specifications do not have to be closely adhered to, but may be varied as needed.
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abraded during the process, etc.) the type of chamber may be modified. In certain cases, ordinary rubber or cork-stoppered round bottles, from 3 to 5 inches in diameter, with glass marbles about 0.75 inch in ,diameter, were used advantageously, as in the pulverizing of bacteria, sugars, and plant materials. Uniform mixtures of soil or semi-plastic suspensions have been produced by subjecting the material to the rolling process in bottles, without the aid of marbles or balls. When larger scale methods are advantageous, a series of roller units may be constructed one upon the other, connected to a single motor.
The rate of grinding and the degree of subdivision depend upon the interrelation of the amount of material inserted, the size and speed of mill, and the number, size, and weight of balls employed. It was found that 0.75-inch steel ball bearings were most generally efficient. Depending upon the materials ground and requirements conditioned by the investigation (freedom from impurities
Acknowledgments The writer wishes to express his thanks to members of the staff of the Division of Plant Nutrition and to V. Arntaen of the Department of Engineering for suggestions given. RECEIVED JuIy 16, 1935.
Constituents of Pyrethrum Flowers J
Determination of Pyrethrin I1 H. L. HALLER AND FRED ACREE, JR. Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Washington, D. C.
S
IKCE the isolation and characterization by Staudinger and Ruzicka (IO) of the insecticidal constituents of pyrethrum flowers, pyrethrin I and pyrethrin 11, nine methods have been proposed for their quantitative determination. Three of these methods determine pyrethrin I and pyrethrin I1 separately; the other six determine the total pyrethrin content. Staudinger and Harder (9) were the first to propose a method for determining the pyrethrins separately. Their method, known as the acid method, is based upon the fact that both the pyrethrins are esters and that on hydrolysis pyrethrin I yields a monocarboxylic acid volatile with steam, whereas pyrethrin I1 yields a dicarboxylic acid which is nonvolatile. The methods of Tattersfield, Hobson, and Gimingham (11) and of Seil (8) are modifications and improvements of the original Staudinger and Harder method. Of the three procedures, that of Seil is the most rapid, and is probably the most satisfactory. A11 three methods tend to give high results because of the presence of fatty acids, which are known to be present in pyrethrum extracts both in the free state and in combination as esters or glycerides ( 7 ) . If the two pyrethrins were equally toxic to insects, it mould be immaterial which method of analysis was used, but most tests indicate that pyrethrin I is more toxic than pyrethrin 11. Determination of the individual pyrethrins, therefore, may give a more accurate insecticidal value of pyrethrum flowers than a determination of the total pyrethrins. It is well known that most methyl esters yield methyl iodide quantitatively on refluxing in constant-boiling hydriodic acid (5, 6). The method proposed in this paper is based upon the fact that pure pyrethrin 11, being a methyl ester, yields, on refluxing with hydriodic acid, the quantity of methyl iodide required by its formula (4). The latter is determined by the volumetric method of Viebock and Schwappach as modified by Clark (S). I n this method the methyl iodide is absorbed in a n acetic acid solution of potassium acetate to which bromine has been added. The following reaction then takes place:
++ +
+
CHJ Brz -+-CH3Br IBr IBr 2Brz 3H20 +HIOa
+ 5HBr
The solution containing the iodic acid is treated with formic acid to remove the excess bromine, potassium iodide is added, the solution is acidified with dilute sulfuric acid, and the liberated iodine is titrated with a standard sodium thiosulfate solution. As 6 atoms of iodine are liberated for each mole of methoxyl (OCH3), 1 cc. of 0.05 N sodium thiosulfate is equivalent to 3.11 mg. of pyrethrin 11. It thus follows that, for pyrethrum flowers containing about 1 per cent of pyrethrins, a 5-gram sample is ample for a macrodetermination. The determinations were made in the apparatus described by Clark (2).
Reagents The following reagents, all of analytical grade, were used in the determinations, and it was considered essential to determine the blank on them: Petroleum ether (b. p. 30" t o 60" C.) Chloroform Phenol Hydriodic acid, sp. gr. 1.70, constant-boiling, which has been treated with hypophosphorous acid t o remove the free iodine. (The hydriodic acid furnished by Merck & Co. has been treated with hypophosphorous acid.) In order to reduce the blank, it is desirable to pass a stream of carbon dioxide through the boiling solution under reflux for 2 or 3 hours. Potassium acetate solution, 20 grams dissolved in 200 cc. of glacial acetic acid Sodium acetate solution,. 25 grams dissolved in 100 cc. of water Bromine Formic acid (at least 90 per cent purity) Sulfuric acid solution, 10 cc. dissolved in 100 cc. of water Potassium iodide ' Sodium thiosulfate solution, 0.05 N
Procedure PREPARATION OF EXTRACT.A 5-gram sample of finely ground pyrethrum flowers was extracted for 7 hours with petroleum
