JANUARY 15, 1938
AN.4LYTICAL EDITION
of the air-carbon dioxide mixture from the beer, and these are
then analyzed in the alkali buret, B. The absorption buret, B, is filled with 15 per cent alkali; gas buret C is filled with 20 per cent sodium sulfate solution acidified with sulfuric acid, and contains a few drops of hexyl alcohol. All tubes and connections are rendered air-free by filling with water. The cap is punctured with the spike in the usual manner, and 100 cc. of gas are permitted to flow into buret C. Stopcock D is then turned and the 100 cc. of gas are diverted into buret B , where the carbon dioxide is absorbed by the alkali and the "air" is measured. Another 100 cc. are permitted to flow into buret C, and the process is repeated as long as carbon dioxide is evolved from the beer at 25" C. When all the gas has been evolved at 25" C., the beer bottle is placed in a boiling dilute aqueous-glycerol bath (102' t o 103" C.). Leveling bulb E is lowered to produce a partial vacuum in C and help draw over any gas from the boiling beer. When all the gas has evolved, the gas mixture is moved into B , the carbon dioxide is absorbed, and increase in air is not,ed. Table I1 gives the results of these experiments on a number of beers. It will be seen that the bulk of the air (70 to 80 per cent) comes over in the first 100 cc. of the gas evolved from the beer, and that by using ordinary care to evolve as much gas as possible a t 25" C., an average recovery of 94 per cent of the total air is possible. It is therefore apparent that this pressure method is not only suitable as an accurate carbon dioxide method, but also gives sufficiently accurate air r e x l t s for most purposes. I n carrying out the air determination in the usual manner the results may be slightly reduced by reason of the absorption of some of the oxygen in the evolved air by the small amount
19
of alkaline beer contained in the absorption buret,. This error is small and except for the most precise work generally needs no correction.
Summary 1. A simple, rapid, and precise pressure method for determining carbon dioxide in packaged beer or other carbonated beverages, which corrects for the air error is further described in detail. 2. The method is suitable for the determination of air in packaged beers and carbonated beverages, and is especially valuable for routine control work. 3. The extent of recovery of the air in bottled beers by this method has been determined, and i t is shown that a n average recovery of 94 per cent may be obtained a t 25" C. 4. A simple primary pressure standard for checking the pressure gages is described. 5. An alignment chart for simply calculating the analytical data is presented.
Literature Cited (1) Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 4th ed., p. 151 (1935). (2) Gray and Stone, S.Assoc. Oficial Ap-. Chem., 19, 162 (1936). (3) Ibid., p. 171. (4) Helm and Richardt, S. Inst. Brewing, 42, 171 (1936). (5) Murray, Ibid., 31, 137 (1925). (6) Siegfried, Schtceit. Brau.-Rundschau, 48, 1 (1937). RECEIVED October 7 , 1937.
Determination of Rotenone in Derris and Cube 11. Extraction from the Root HOWARD A. JONES, Bureau of Entomology and Plant Quarantine, Beltsville, Md., AND J. J. T. GRAHARI, Food and Drug Administration, U. S. Department of Agriculture, Washington, D. C.
S
ISCE the publication of the earlier methods for the ana-
lytical extraction of rotenone from derris and cube roots using Soxhlet extraction with ether (9) and with carbon tetrachloride ( 6 ) as solvents, various other procedures have been proposed. Danckwortt and Budde (4) have used roomtemperature extraction with a given weight of chloroform followed by filtration and removal of an aliquot of the filtrate by weight. Cahn and Boam ( 3 ) have suggested Soxhlet extraction with trichloroethylene. I n a method proposed by Rowaan (10) the sample is extracted a t room temperature with successive lots of chloroform. The method of Beach (1) is similar to that of Danckwortt and Budde except that an aliquot of the filtrate is taken by volume. Worsley (12) has used percolation with hot ethyl acetate, and Begtrup ( 2 ) proposes percolation with toluene a t room temperature. Recently Seaber (11) has presented results by various extraction procedures and has stated Beach's method to be preferable. The object of the present work was to qtudy some of these methods of extraction and others already in use in the writers' laboratories with a view to deciding on the best procedure to be used in conjunction with the crystallization method already published ( 7 ) .
Extraction AIethods It has been known for some time that Soxhlet extraction with carbon tetrachloride for as much as 24 hours does not always completely recover the rotenone. It is also generally
supposed that some of the rotenone may decompose during the long boiling necessary in such an extraction. Accordingly some test's were made of a method partially overcoming t,his objection in which most of the extract was removed and not subjected to continued boiling. The flask containing the extract was changed after 3 hours and the extraction continued for the usual length of time. I n addition to Soxhlet extraction, four other general methods of extraction were tested : 1. BOILIXG-MULTIPLE EXTRACTION METHOD.The sample was refluxed with the solvent under a condenser on the steam bath for 1 to 2 hours and filtered by suction. The marc was washed on the filter with hot solvent and then refluxed again with fresh solvent, followed again by filtration and washing. This was followed by a third refluxing, filtering, and washing. 2. BOILIKG-ALIQUOT METHOD. The sample was treated with a weighed amount of solvent and refluxed under a condenser on the steam bath for 2 to 3 hours. After the solution had cooled to room temperature, solvent was added to replace that lost, until the mixture was brought' to its original weight,. The extraction mixture was chilled in the refrigerator, filtered through folded filter paper, precautions being taken to prevent loss by evaporation, and an aliquot of the filtrate was t,aken by volume. 3. R O O M TEMPER.4TURE-MULTIPLE EXTRACTION hIETHOD. This method was similar to method 1 but was carried out at room temperature. 4. ROOMTEMPERATURE-ALIQUOT METHOD. This was substantially the method proposed by Beach. The sample mas shaken with an accurately measured volume of solvent, the time of shaking ranging from 4 hours to overnight. The remaining procedure was the same as in method 2.
INDUSTRIAL AND ENGINEERING CHEMISTRY
20
The weight of the sample used in these methods ranged from 10 to 30 grams, depending on the amount of rotenone known to be present. This variation in sample with rotenone content is not necessary but was merely adopted for convenience. The volume of solvent in cubic centimeters used in the aliquot methods was about ten times the weight of the sample in grams. I n the multiple-extraction methods this volume of solvent was used for each successive extraction; in the aliquot methods the volume of the aliquot taken was two-thirds that of the original solvent. I n all methods except those using carbon tetrachloride as solvent, after most of the original solvent had been recovered by distillation the extract was evaporated to dryness, taken up in carbon tetrachloride, and again evaporated to dryness. This process was repeated two more times. I n the senior author's work the extracts were evaporated to dryness on the TABLEI. ROTENONE CONTENT OF A SAMPLE OF DERRISROOT (No. 3307) Method Soxhlet, Continuous for 24 hours Flasks changed after 3 hours Boiling-multiple extraction
Boiling-aliquo t Room temperature-multiple extraction Room temperature-aliquot
6
Test of Rotenone Marc % ._
Solvent Carbon tetrachloride
6.2
Carbon tetrachloride Benzene Carbon tetrachloride Chloroform Ethylene dichloride Trichloroethylene E t h y l acetate Benzene-alcohol azeotronic mixture Benzene
7.0 7.1 6.4 6.8 6.9 6.7 6.7 6.90 6.9
Chloroform 7.4 Chloroform 7.4 Benzene 7.0 E t h y l acetate 7.5 Solvate very impure compared with t h a t from other methods.
0
.. 2
.. .. ..
VOL. 10, NO. 1
steam bath and then placed under suction momentarily while hot to aid in removal of the solvent. I n the junior author's analyses the last 20 to 25 cc. of solvent were evaporated under vacuum. Occasionally there was extracted by chloroform a t room temperature a small amount of material that was insoluble in hot carbon tetrachloride. This occurred more frequently with cube roots than with derris roots. I n such cases the carbon tetrachloride solution of the extract was filtered hot and the residue washed thoroughly with hot carbon tetrachloride. Rotenone was then crystallized from the extract in the form of the carbon tetrachloride solvate by the procedure already published ( 7 ) . As this procedure includes determination of the purity of the solvate by alcohol recovery, the results obtained were for pure rotenone. The marcs from the multiple extractions were tested for rotenone. They were boiled with acetone for a t least one hour and filtered, and the filtrate was evaporated to dryness. This extract was dissolved in an amount of acetone such that 1 cc. was equivalent to 2.5 grams of the original root sample, and portions of this solution were tested by the modified Durham color test (8). Results of the tests were grouped in five grades: 0, negative; 1, faintly positive; 2, medium positive; 3, strongly positive; 4,very strongly positive. It has been the writers' experience that marcs giving tests designated as 1 and 2 do not contain sufficient rotenone to affect the results appreciably. If a test designated as 3 or 4 was obtained, the extraction was not considered satisfactory. The criticism that Cahn and Boam (3) made of the Durham test does not hold here, as in these tests blue-green or green colors, as well as blue, were considered positive. No tests of the marcs from the aliquoting procedures were possible because of the retained mother liquor.
TABLE11. ROTENONE CONTENT OF POWDERED SAMPLESOF DERRISAND CUBE
Sample Derris 998 999 1000 2120 2121 2288 2700 2701 2710 2715 2802 2803 3000 3001 3002 3006 3007 3126 3307 3354 3355 Cube 2119 2664 2665 2711 2714 2801 3003 3004 3005 Timbo 3230 3260 Cube 3449 3596
Teuhrosra
,----AliquotSenior author
Chloroform-Room Temperature----Benzene-BoilingMultiple Extraction hfultiple Extraction Junior Test of Test of .4v. Analysis marca Analysis marca Aliquot author
%
%
%
%
0.5 0.5 0.6 8.0 10.0 0.4 4.3 6.2 3.3 6.0 2.5 4.0 4.3 5.2 1.9 3.6 0.5 5.7 7.2 0.7 3.2
.. ..
..
..
.. ..
10.4 0.4 4.6
ic:0 10.2 0.4 4.4
3:2 6.2 2.7 3.9 4.4 5.5 2.1 3.6 0.6 5.9 7.5 0.6 3.6
3:2 6.1 2.6 4.0 4.4 5.4 2.0 3.6 0.6 5.8 7.4 0.6 3.4
4.4 3.6 2.9 2.8 5.4
5.1 4.5 2.3 2.0 4.7 3.9 2.8 3.0 5.7
5.0 4.4 2.4 1.9 4.6 3.8 2.8 2.9 5.6
3.5 4.3
4.0 4.4
3.9 4.4
3.1 3.7
3.4 3.9
3.2 3.8
5.0 4.2 2.4
1.8
8:O
s:2 10.3
%
..
.. .. 0 0
.... .. .. .. .. ..
..
5:3
1
..
.. 5:9 7.4
....
.. ..
.. .. .. .. .. ..
.. .. 1
2 .. ..
.. .. .. .. ....
.. .. ..
5:4
1
..
.. .. .. ..
..
..
7:s
.. .. ..
3.2
.. .. ..
5.4 2.0 3.7
5:s 7.1 3.4 4.7
.. ... . .. ..
.. 2
..
..
.. .. .. .. .. .. .. 0 0 0
1 2
.. .. .. .. .. ..
..
.. .. .. ..
13.4 11.5 13.0 22.6 30.4 16.2 13.6 18.4 15.5 17.0 14.0 13.9 15.9 14.5 11.9 15.7 12.8 15.7 19.0 12.9 10.6
4 4 5 35 34 2 32 34 21 36 19 29 28 36 17 23 5 37 39 32
5.8 6.4 6.7 6.4 6.8 5.7 5.7 6.5 7.0 7.2 5.7 4.9 7.7
26 32 22 20 33 31 18 18 32
+:3 8.3 6.7 7.0 7.2 7.4 7.4 5.6
..
.. .. .. ..
.. .. .. ..
.. ..
3.6 4.6
0 0
.
..
..
5:1
4.8
5.2
.. i :2
i :3
5 :7 7.5
.. ..
..
1
..
.. .. .. .. .. ..
0
5.6
..
.. .. .. .. .. .. .. .. .. .. .. ..
..
2:s
..
%
7.0
.. .. .. .. ..
..
%
..
..
Moisture
%
6.9
*.
Ratio of Rotenone to Total Extract
%
..
..
Total Benzene Extract
%
..
..
Ethyl BenzeneAcetateRoom Room Tempera- TemperaturetureBliquot Aliquot
..
..
.. ..
.. .. ..
..
..
..
..
3:2
..
..
.. ..
.. .. ..
e:6 . i4
..
.. .. ..
5 .'S
5 :5
19.3 13.6 10.8 9.4 13.8 12.2 15.9 16.5 17.6
..
.. ..
18.8 20.6
21 21
6.5 7.8
..
..
7.2 18.7
44 20
8.5
..
7.3
19
7.4
..
.. .. .. .. ..
.. .. .. .. ..
I
4:5
5
% ..
.. .. ..
iirginianrr 3107 1.3 1.4 .. .. .. .. .. 1.4 0, negative; 1. faintly positive; 2, medium positive; 3, strongly positive: 4 , very strongly posltive.
..
JANUARI- 15, 1938
ANALYTICAL EDITION
I n Table I results are given for a sample of poxdered derris root (No. 3307) extracted by these methods with various solvents. As judged by the test on the mares, the 24-hour Soxhlet extractions with carbon tetrachloride were incomplete. Comparison of the results by the continuous Soxhlet extraction with that in which the flasks were changed indicates that there may have been some decomposition in the continuous extraction. As a further example of the incompleteness of carbon tetrachloride Soxhlet extraction, the marc from one sample of derris root (No. 3095) was found to contain over 1 per cent of rotenone, by subsequent actual extraction and crystallization, after both 24-hour and 48-hour Soxhlet extractions. However, this sample, containing about 8 per cent of rotenone, was the most difficult to extract of all the samples encountered in this work. I n the boiling-multiple extraction method the removal of rotenone as judged by the test on the marc was satisfactorily complete with all solvents tested except carbon tetrachloride. With the benzene-alcohol azeotropic mixture, however, the solvate obtained was of very low purity. The room-temperature extractions with chloroform and ethyl acetate gave results slightly higher than any of the other methods. At the time this work was begun the boiling-multiple extraction method with benzene was favored. These results indicated, however, that room-temperature extraction might be a t least as efficient as the boiling extraction. From the standpoint of ease of handling and avoidance of decomposition the room-temperature extraction undoubtedly was better. Further, the aliquoting procedure seemed convenient and less time-consuming. $ccordingly a more detailed study of some of these methods on a large number of samples was undertaken, with particular emphasis on the room temperature-aliquot method using chloroform.
21
TABLE 111. EFFECT OF TIMEOF SHAKING CPON THE ROTENONE CONTENT O F A SAMPLE O F DERRISROOT(NO. 3307) (Determined by the chloroform-room temperature-aliquot method) Time of Shaking Rotenone Hours % 0.25 6.6 6.6 0.5 1 6.8 2 6.9 4 6.8 7 7.0 About 18 (overnight) 7.2
introduce no appreciable errors is shown by the agreement of results with those of the corresponding multiple-extraction method.
TIMEOF SHAKING IN THE ROOM TEMPERATURE-ALIQUOT METHOD. Beach's method calls for shaking the mixture of
root and solvent for 2 or 3 hours, allowing the mixture to stand overnight, and then shaking for an additional hour. The junior author in most cases adhered to Beach's procedure, using a total of 4 hours' shaking. The senior author, however, used overnight (18 hours) continuous shaking. T o determine the effect of time of shaking on the results, portions of a sample of a powdered derris root (No. 3307) were shaken with solvent for different periods of time, after which each mixture was chilled for 30 minutes and filtered as usual. The results, compared with those for overnight shaking, are shown in Table 111. It might appear that in general more rotenone was extracted during the longer periods of shaking, but the differences are so small that for practical purposes equilibrium might be considered to have been reached in about 2 hours. For convenience, however, and to ensure complete extraction, the overnight shaking seems preferable. EFFECTOF FIXENESS OF THE SAMPLE.The chloroformDetailed Examination of Methods room temperature-aliquot procedure has been shown to be COMPARISOX OF ROOMTEMPERATURE-ALIQUOT METHOD satisfactory for powdered samples. The manufacturers who supplied these samples claim to be grinding so that about 90 WITH OTHER PROCEDURES. Results of analyses made on 35 per cent will pass a 200-mesh sieve. At any rate, these samples of powdered derris, cube, and Tephrosia roots are samples were sufficiently fine so that 100 per cent passed a 60given in Table 11. T h a t room temperature-chloroform exmesh sieve. When, however, this method, with overnight traction is complete on such samples is shown by the fact that shaking, was applied to certain more coarsely ground samples, the results agreed with those by the benzene-boiling-multiple the results were disappointing. extraction method, the mares from which showed practically Table IV shows the results for such samples, together with complete extraction, and also by the fact that mares from the the fineness in terms of the percentage passing a 60-mesh sieve. chloroform-room temperature-multiple extraction method I n a number of these samples results by the chloroformshowed practically complete extraction. That evaporation room temperature-aliquot method were markedly lower than during filtering and the withdrawal of an aliquot of the those by the chloroform-room temperature and benzenefiltrate in the chloroform-room temperature-aliquot method TABLE Iv. ROTENONE CONTENT
O F COARBELY
Before Regrinding Rotenone Content
Sample
Passed 60Mesh
Derris 3095 3493 3494 3495 3496 3584 3694 Cube 686--1 Timho 2604 2505 Cube 3595 a 0, negative;
Benzene-Boiling Chloroform--Room Temperature-Multiple Multiple Extraction Extraction Test of Test of Aliquot Analysis marca Bnalysis marc" Aliquot
%
Chloroformboilingaliquot
%
%
%
98 s5 87 90 83 95 57
5.2 4.4 6.6 6.4 8.9 4.0
8.2 6,9 7.0 10.2 9.9
5.8
i:9
1
7.7 5.2 6.4 9.2 9.7 4.0 6 5
90
10.9
10.9
1
10.7
1
40 46
8.8 3.6
11.0 5.3
4 3
9.8 4.4
4 3
9.6 4.7
9.0
71
1.5
..
,.
1.1
1
,.
..
0
0 0
1 3
..
0 3 1
4 3
0 2
GROUNDS.4MPLE.9
OF
DERRISAND
Aee--.\fter RegrindingtoneEthyl -Rotenone Content,Ratio of Chloroform- Room room acetatetemroom Total RoteTemperature peratemPassed llultiple Extraction Benzene none t o Exture- perature- ' 60Test of Total tract Extract aliquot aliquot mesh Aliquot Analysis marc"
%
%
%
%
%
6.9 4.5 6.0 8.0 8.6
..
..
.. .. .. .. .. ..
93 98 98 97
6.2 9.1 9.4
..
..
. ..
,
..
8.'6
.. .. .. .. ,.
CUBE
..
7,'s
.. .
I
,.
5.5
..
.. ..
9.2
..
..
..
%
%
5.2
.. .. ..
%
..
.. .... ..2 ,. ..
..
..
..
..
24.7
44
90
11.6
..
2
..
28.3 16.3
39 32
..
..
9.8
11
..
..
..
97
9.6 4.5
1.5
,.
..
1, faintly positive; 2, medium positive; 3, strongly positive: 4, very strongly positive.
%
6,'s ..
17.1 14.0 16.3 21.7 24.3 13.2 15.8
48 42
47 41 30 37
43
22
INDUSTRIAL AND ENGINEERIXG CHEMISTRY
boiling-multiple extraction methods, even where extraction by the last two methods was unsatisfactory. Some of the samples showing this incomplete extraction were reground in a Wiley laboratory mill and again analyzed, with the results also shown in Table IV. Results by the chloroform-aliquot method were in general higher than before regrinding but were still lower than those by the chloroform-multiple extraction method before regrinding. Two of the samples which were among the most difficult to extract were analyzed by the chloroform-multiple extraction method after being reground and extraction was found to be slightly more complete than before regrinding, as judged by the tests on the marc. These results definitely demonstrate that on coarse samples such as these more complete extraction is obtained by the chloroformmultiple extraction method than by the aliquot procedure. That coarseness of the sample alone does not necessarily lead to incomplete extraction is shown by some of the results in Table IV. Thus, sample 3594, which was very coarse, gave satisfactory results by the chloroform-room temperature-aliquot method as judged by comparison with results by the benzene-boiling-multiple extraction method and the chloroform-room temperature-multiple extraction method. On the other hand, sample 3095, which was considerably finer, gave markedly low results by the first method. It is evident from the results in Table IV that, regardless of the method used, samples must be finely ground to give complete extraction. Probably a sample should be ground so that a t least 95 per cent of it passes a 60-mesh sieve. Grinding to this fineness may be accomplished in the Wiley laboratory mill. When the usual run of samples is ground to this fineness, i t may be expected that satisfactory extraction will be obtained by the chloroform-aliquot procedure. If, however, the rotenone content is unusually high, as discussed in the next section, or for any other reason there is doubt as to the completeness of extraction, the analysis should be made or checked by the chloroform-multiple extraction method. The results obtained here indicate that this method, although less convenient and more time-consuming than the aliquot procedure, can be relied upon to give complete extraction if the sample is ground to the fineness specified. EFFECTOF R.4TIO O F ROTEXOSE TO TOTAL EXTRACT ON COhfPLETEXESS O F EXTRACTION. Sample 3095, which although finer than some of the other samples did not give complete extraction by the chloroform-room temperature-aliquot method, had the highest ratio of rotenone to total extract of any of the samples studied. Likewise sample 3495, in which the ratio of rotenone to total extract was also high, gave unsatisfactory results by the same method, even after regrinding to the fineness of sample 3095. I n calculating this ratio the value for rotenone by the chloroform-room temperature-aliquot method was used for the powdered samples, and that by the chloroform-room temperature-multiple extraction or the benzene-boilingmultiple extraction method for the coarsely ground samples. Benzene extractives were determined by Soxhlet extraction of 5-gram samples. I n general, the amount of total benzene extractives appears to be about the same as that of the total ether and total chloroform extractives. Some evidence has already been obtained, in making Soxhlet extractions of small samples for total extractives, that, even among the powdered samples, those containing the higher percentages of rotenone were more difficult to extract. This may explain the unsatisfactory results on the two samples mentioned. It is possible that, if these samples could have been ground to the degree of fineness of the finely powdered samples in Table 11, complete extraction by the aliquot procedure might have been obtained. Equipment for accomplishing this with small samples is not readily available, and in lieu of this it seems that samples should be checked by the chloroform-room
VOL. 10, NO. 1
temperature-multiple extraction method when the ratio of rotenone in the total extract is about 40 per cent or over. Such samples are unusual, however. I n a recent article reporting the analysis of 190 samples of derris root, Georgi (5) found the maximum ratio of rotenone to total extract (ether) to be 39 per cent. RELATIVEEASEOF EXTRACTION OF DERRIS AND CUBE. In general cube and timbo roots are much more readily extracted of their rotenone content than is derris root. Thus, in Soxhlet extractions of small samples most solvents: completely extract the rotenone from cube and timbo whereas many of these solvents do not give complete extraction of derris roots, as indicated by color tests of the marcs. The results in Table IV for cube root 686-4 a sample of only medium fineness in which the ratio of rotenone to total extract was very high, indicate that these factors are not so serious in causing incomplete extraction as in the case of derris roots. It was observed that a t 0" C. the solvate crystallized more slowly from cube extracts than from derris extracts of comparable rotenone content.
Accuracy and Precision of Methods 90attempt was made to study the accuracy of the extraction procedures. Because of the practical impossibility of determining the exact amount of rotenone in a given root by any method now available, such a study would be difficult and unsatisfactory. It can only be stated that on the powdered samples studied the chloroform-room temperature and the benzene-boiling-multiple extraction methods seem to give satisfactorily complete extraction and that, since results by the chloroform-room temperature-aliquot method agree with these, it may also be presumed to give satisfactory extraction. Only the chloroform-room temperature-aliquot method was studied extensively enough to permit a definite conclusion as to precision. Replicate results on a sample by a single investigator in general agreed within about 5 per cent. Results by the junior author were in general slightly higher than those obtained by the senior author (Table 11). At various points in both the extraction and the crystallization the procedures used by the two authors were slightly different. Thus in the extraction the senior author used overnight shaking, while the junior author used a total of 4 hours' shaking interrupted in most cases by overnight standing. I n a few determinations the junior author did not chill the extracts before filtering. The chilling of the original mixture before filtration seems advisable from another standpoint than merely to prevent loss by evaporation. It was found that in some cases in which this preliminary chilling was not made the filtration of the solvate a t 0" C. was slow and difficult, whereas the solvate from the same sample filtered readily when the chilling was employed. Evidently the preliminary chilling separates waxes or resins from some samples t h a t would otherwise separate during the crystallization at 0" C. and interfere with the filtration of the solvate. The senior author used the vacuum after each evaporation of the extract in the earlier analyses, whereas the junior author made the entire evaporation under vacuum in all cases. For the crystallization the senior author added a volume of carbon tetrachloride numerically equal in cubic centimeters to the weight of the sample in grams, while the junior author made the extract to this total volume by the addition of carbon tetrachloride. The average difference between the results by the two authors was only about 3.5 per cent. I n view of the many slight differences in procedure, the two sets of results may be considered to be in good agreement. I n general i t would seem that results by two investigators should agree within about 5 per cent.
JANUARY 15, 1938
ASALYTIC.4L EDITION
Moisture Content of Powdered Derris and Cube Roots I n Table I1 are given the values for moisture content of the powdered derris and cube roots determined by drying 2-gram samples a t 106" C. for 2 hours. Two days' additional drying of some of the samples caused no significant additional loss in weight. It will be noted that the values range only from 4.9 to 8.5 per cent. I n view of this small variation the rotenone values have not been corrected for moisture content of the sample. Work done in the writers' laboratories indicates that it is preferable not to dry the sample before extraction. I n cases in which a preliminary drying has been made the results for rotenone and the purity of the separated solvate have usually been slightly lower than on the undried root. There are indications also that drying renders extraction more difficult. Some samples were dried a t 100" C., and others a t 50" C . under vacuum. I t is possible that drying a t room temperature, such as in a vacuum desiccator, would not interfere with the rotenone determination. Such drying, however, seems unnecessary for the analysi- of the usual samples received in this country.
Summary and Conclusions I n the analysis of finely powdered samples of derris and cube roots a method involving treatment with chloroform a t room temperature followed by removal of an aliquot of the filtered extract gives satisfactorily complete extraction of the rotenone. Fineness of the sample is a n exceedingly important factor in obtaining complete extraction by any method. If coarse samples are ground so that a t least 95 per cent passes a 60-
23
mesh sieve, they will usually give satisfactory extraction by the aliquoting procedure. Samples containing a high ratio of rotenone to total extractives were found to be more difficult to extract than those with loTver percentages of rotenone. T h e n the ratio of rotenone to total extract was about 40 per cent or over, particularly in the case of derris roots, it was necessary to employ extraction a t room temperature with successive lots of chloroform in order to obtain satisfactory extraction of the rotenone. This method should also be employed as a check whenever there is doubt as to the completeness of extraction by the aliquoting procedure. Cube roots in general are more readily extracted of their rotenone content than are derris roots. The moisture content of derris and cube roots as received in this country has not been found to be sufficiently great to interfere with their analysis, and hence preliminary drying of samples seems unnecessary.
Literature Cited Beach, D. C., Soap, 12, N o . 7, 109, 111-12 (1936). Begtrup, F. L . , Dansk Tids. Farm., 11, 6-12 (1937). Cahn, R. S.,and Boam, J. J., J . Soc. C h e m In?., 54, 37-42T (1935).
Danckwortt, P. W,. and Budde, H., Deut. Tiertirztl. Tochschr., S o . 43, 677 (1933). Georgi. C. D. V., Lambourne, J., and Teik, G. L., X a l a y a n 4 g r . J., 25, 187-200 (1937). Jones, H. A , . ISD.ESG. C H E X I . , Anal. Ed., 5,23-6 (1933). Jones, H. .A,, Ibid., 9 , 206-10 (1937). Jones, H . A , , and Smith, C . M., I b i d . , 5, 75-6 (1933). Roark, R . C . . Mafalayan Agr. J . , 18, 455-8 (1930). Rowaan. P. A., Cliem. T e e k b l a d , 32, 291-5 (1935). Seaber, W. M., J . SOC.Chem. Ind., 56, 168-73T (1937). Torsley, R . R . LeG., Ibid., 55, 349-57T (1936). RECEIVED December 10, 1937.
Standardizing Silver Nitrate Volumetric Solution ROBERT D'ORAZIO 767 East 237th St., New York, N. Y.
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HE author has used to good advantage the following short method for the standardization of volumetric silver nitrate. A volumetric hydrochloric acid solution is exactly neutralized, using a standard alkali solution. The chloride salt formed is then determined by titrating with a volumetric, silver nitrate solution, using potassium chromate as indicator. The number of cubic centimeters of hydrochloric acid is exactly equivalent to the number of cubic centimeters of standard alkali, which, in turn, is exactly equivalent to the number of cubic centimeters of silver nitrate. Thus, if any one of the above is known, the other two can be determined. The author used this method to standardize silver nitrate against sodium hydroxide standard volumetric solution, for chloride determinations. Sodium hydroxide was used as the standard in preference to hydrochloric acid, since in this particular laboratory standard hydrochloric acid was not available as a stock reagent. Place 25 cc. of 0.1 -V hydrochloric acid, accurately measured from a buret, and about 25 cc. of distilled water in an Erlenmeyer flask of about 200- to 300-cc. capacity. Vsing phenol-
phthalein test solution as indicator, titrate to a faint pink with the standard 0.1 N sodium hydroxide volumetric solution. Add 2 cc. of a 5 per cent potassium chromate test solution and titrate with the silver nitrate solution, to the first red tinge. The cubic centimeters of silver nitrate, consumed in the titration, are exactly equivalent to the cubic centimeters of the standard sodium hydroxide. When checked against the thiocyanate volumetric method and the silver chloride gravimetric method, good results were obtained and the time required was only a few minutes as against hours in these two other methods. This principle can also be applied to the standardizations of potassium permanganate and oxalic acid volumetric solutions, by neutralizing the volumetric oxalic acid with the standard alkali, and determining the oxalate salt formed by titration with the potassium permanganate solution. The only precaution here is to use a nonreducing indicator in the oxalic acid-alkali titration, so that it will have no effect on the subsequent permanganate titration. It follows that the cubic centimeters of oxalic acid are exactly equivalent to the cubic centimeters of standard alkali and of permanganate. RECEIVED August 17, 1937.
