ANALYTICAL EDITION
February 15, 1941
TABLE 111. COMPARISON OF ENDPOINTS (Solution added: NaOH. approximately 0.01 N ) Solution Titrated End-Point Ratios(Approximate HydrogenTungstenPhenolNormality) calomel silver phthalein MZ.acid per ml. base 1.021 t 0.002 1,021 1.032 t 0.001 0.01 "?SO4 0.6906 0.6926 f 0,0006 O.OlNHC1 0.6918 & 0.0008
tion of sodium carbonate (0.5 AT) with hydrochloric acid ( N ) to determine precisely the electrical end point corresponding to the phenolphthalein end point. At the methyl orange end point of the carbonate titration, however, the tungsten-silver system gave a definite, reproducible electrometric end point. To determine the accuracy, as well as the precision, of the tungsten-silver electrode system in titrations of dilute solutions of strong acids, a comparison was made of end-point ratios obtained by the use of hydrogen-calomel, tungsten-
107
silver, and phenolphthalein, respectively. These data appear in Table 111. Summary The tungsten-nickel electrode system has not been found satisfactory in neutralizations involving dilute solutions. The tungsten-silver system appears to furnish precise and accurate electrical end points in titrations of strong acids by strong bases as dilute as 0.001 N , and vice versa for 0.01 N solutions. I n titrations employing more concentrated solutions the system is of value in the neutralization of strong acids by ammonium hydroxide, of acetic acid by a strong base, and of sodium carbonate.
Literature Cited (1) Closs and Kahlenberg, Trans. Electrochem. Soc., 54, 369 (1928) (2) Fuoss, IND.ENQ.CHEM.,Anal. Ed., 1, 125 (1929). (3) Furman and Low, J. A m . Chem. SOC.,55, 1310 (1933). (4) Holt and Kahlenberg, Trans. Electrochem. Soc., 57, 361 (1930). (5) Kahlenberg and Krueger, Ibid., 56, 201 (1929).
Extraction and Determination of Pyrethrin I in Ground Pyrethrum Flowers An Improved Apparatus JETHRO S. YIP, Division of Plant Xutrition, University of California, Berkeley, Calif.
M
E' I
S&mm
-
I I 3
mm.
FIGURE1. AUXILIARYCONDENSER
ANY of the more reliable methods (1-4) developed in recent years for the extraction of pyrethrum flowers for analysis recommend the use of low-boiling-point petroleum ether (20" to 40" C.) as a solvent, because it can completely remove the pyrethrins without removing other substances which will interfere with the method subsequently employed for the pyrethrin determination, and this solvent may itself be easily removed with the least amount of heat, so that there is little chance of loss of the pyrethrins. A simple and inexpensive modification of an apparatus for the extraction and determination of pyrethrin I in ground pyrethrum flowers is proposed. The objects of the changes ;;e primarily to reduce the loss of petroleum ether used for extraction and t o eliminate transfer of the extracted and subsequently refluxed solution to a larger container for alcohol removal. Modifications of the condenser amount to insertion of a cold-water column into each condenser and use, as a receiving flask, of a 500-cc. Kjeldahl flask with the same size of interchangeable ground-glass joints as in the rest of the apparatus. Frothing during the evaporation of alcohol is reduced and less attention is required. The use of a Soxhlet with either an Allihn or a Graham condenser, all with ground-glass joints, in a 7- or 8-hour extraction of ground pyrethrum flowers with low-boiling-point petroleum ether has heretofore resulted in a 60 to 75 per cent loss of a 150-cc. volume of solvent used, especially during warm weather (29.44" C., 85" F., or above) or whenever the temperature of water used for circulating in condensers is much above 25" C. This has been due chiefly to inefficient or insufficient cooling surface in the condenser rather than to leakage in glass connections. To remedy the difficulty without increasing the length of the condenser so as t o make the height of the apparatus too great for convenient handling, a double tube equivalent in length (30 t o 42.5 cm., 12 to 17 inches) to the Allihn condenser, and of a diameter to allow a clearance of 2 to 3 mm. at the bulb constrictions, was constructed (Figure 1). It can be inserted into the condenser to the bulblike enlargement that acts as a rest point, and then
Vd. 13, No. 2
INDUSTRIAL A N D ENGINEERING CHEMISTRY
108
ing, which always takes place during the removal of alcohol with heat and requires much attention to prevent loss of sample. If a 500-cc. Kjddahl flask, specially made with the same size of ground-glass joint as that of the Soxhlet and Allihn condenser, is substituted for a reeeivingflssk in the initid extraction, refluxing and subsequent removal of the alcohol after the addition of water tention, but this soon diminishes as the removsrlAeontinues,ac~~~~.~ . ~~~
immersed in a water bath (45"t o 50' C.)restine on an electric hot plate, with a slow contincous stream df cold Eater flowing into the bath t o replenish the loss of water due t o evaporation and at the same time prevent the temperature of the bath from rising very much above the desired range. Using the modified apparatus, the loss of ether and volume required for extraction have been reduced approximately 50 and 33 per cent, respectively. I n addition, little attention is required during the removal of alcohol by heat. These modifications have resulted in greater economy, considerable saving of time, and elimination of a health hazard in the excessive escape and possible accumulation of fumes of a highly volatile solvent. FIonRE 2.
sui
EXTRACTOES IN OPERATION MODIFICATIONS
WITB
CON.
Acknowledgment
DENSER
single unattached condenser modifier at extreme right
connected to receive the outflow of cold circulating water from the AUihn condenser before it goes into the next condenser. This modification has the effect of a double condenser, or a. condenser within a condenser. According t o several published tunalytical methods (1-4), the extracted material after complete removal of the solvent must he refluxed with 0.5 N alcoholic sodium hydroxide and then, with about 100 cc. of water, transferred to a container (500- to 800-cc. beaker) large enough to accommodate froth-
The author is indebted to R. McCready for the suggestions and constrnction of the type of condenser modifier used. Assistance in the preparation of the experimental and eleriea1 work was furnished by the personnel of Work Projects Administration Official Project No. 65-1-08-91-B-10.
Literature Cited (1) Holaday, D. A., IND.ENQ.Cnm., Anal. Ed., 10, %6 (1938). (2) Seil. H. A.. Soap. 10 (5). 39, 91, 111 (1934). (3) Tattersfield, F., and Hobson,,R. P.. J . Agr. Sci.. 19. 433-7 (1929). (4) Wilooron. F.. Conbib. Boyce ThmnpsonInnst.,8, 17%81 (1936)
New Photoelectric Fluorimeter and Some
Applications FREDERICK KAVANAGH New York Botanical Garden, New York, N. Y.
F.
LUORIMETRIC methods of quantitative analysis have
increased in popularity in recent years. These methods must he used when the substances t o he determined are present in such small amounts that colorimetric methods cannot he used, but are limited to substances which fluoresce when irrsdiated by light of the proper wave lengths, usually between 3000 and 4500 A. Fluorimeters of two general types are in use. One type of instrument depends on a visual comparison of an unknown with a standard of fluorescence. When the unaided eye is used to determine the match of unknown and standard, the sensitivity of the method is low and decreases with increasing concentration. The use of an instrument such as the modified colorimeter of Josephy (7) or a Pulfrich photometer (fS) increases sensitivity and accuracy of match over those possible by the unaided eye. The other type of instrument employs a photocell and galvanometer to measure the fluorescence. Most European
workers use the Cohen ( 1 ) fluorimeter, a simple instrument with a test tube to hold the fluorescing solution. The fluorescence is measured by a barrier-layer photoelectric cell and a high-sensitivity galvanometer which can he used only a t one tenth to one fiftieth the full sensitivity because of fluctuations of lamp intensity (4). I n the Hennessy and Cerecedo (3) modification, a cuvette with rectangular faces holds the fluorescing solution; and, apparently, the galvanometer can be used a t full s e n s i t i ~ t y . Hand (P), however, uses an instrument in which a relatively insensitive pointer type of galvanometer is the measuring instrument. To obtain consistent results with these instruments, the lamp intensity must remain constant long enongh for a measurement to be made of the unknown and then of the standard. By measuring the fluorescence of an unknown solution in terms of a standard of fluorescence, galvanometer drifts and sudden movements caused by changes in lamp intensity can he eliminated. If the ratio of the fluorescence of an unknown
