V O L U M E 19, NO. 10
808 sensitive for 10%. In a consideration of the usefulness of the biological method as a screening device for the elimination of negative saliva samples from race horses, however, it must be clearly kept in mind that the values in Table I1 are amounts per mouse for the biological method and amounts per sample for the chemical method. In these experiments 1.0 ml. of drug-saliva solution was injected into each mouse. I t would not be physiologically permissible to increase this volume by more than 100yo. The amount of drug-saliva solution chemically analyzed was 100 ml., which is the minimum size of the average, routine, saliva sample collected a t race tracks. The significance of these volumes is immediately apparent. If 1.0 or even 2.0 ml. of any of the drug-saliva solutions containing the “positive” amount of drug for the chemical method were injected into mice, in only two instances, diacetylmorphine and nicotine, would even threshold responses be detectable. Saliva is produced by a secretory process by the salivarq glands. I t is not known to what extent drugs Aay be concentrated in this secretion if they are eliminated from the body by this route. I t is conceivable that small doses of drugs administered to a horse may be sufficiently concentrated in the salivary secretion to be detected by the biological method and correspondingly more readily by the chemical method. However, the ex-
perience of the laboratory in the analysis of a large number of saliva samples, both official and experimental, which were found to contain drugs, indicates that drugs are seldom present in such amounts. It is also possible that the breakdown products of drugs may be eliminated in the saliva and that these may have apparent effects on mice and yet not be detectable by the chemical methods employed. Until such time, however, as these possibilities have been demonstrated experimentally, the biological method does not seem justifiable for the detection of drugs in horse saliva. LITERATURE CITED
(1) Autenrieth, W., “Laboratory Manual for Detection of Poisons and Powerful Drugs,” tr. by W. H. Warren, 6th American ed.. Philadelphia, P. Blakiston’s Son & Co., 1928. (2) Munch, J. C., “Bioassays. A Handbook of Quantitative Pharmacology,” Baltimore, Williams & Wilkins Co., 1931. (3) Munch, J. C., J . Am. Pharm. Assoc., 24, No. 7 , 557 (July 1935). (4) Munch, J. C., personal communication. (5) Peterson, F., Haines, W. S., and Webster, R. W., “Legal Medicine and Toxicology,” 2nd ed., Philadelphia, W. B. Saunders Co., 1923. (6) Stephenson, C . H., “Some LMicrochemicalTests for Alkaloids,” Philadelphia, J . B. Lippincott Co., 1921. RECEIVEDSeptember 23, 1946.
Efficient Apparatus for leaching Samples with Water H4IFORD L . HOL3IES’ AND HARRY W. ROBBIUS, Special Guayule Research Project, Bureau of Plant I n d u s t r y , Soils a n d Agricultural Engineering, IT. S. D e p a r t m e n t of Agriculture, Salinas, Calij. connection with the analysis of guayule shrub for rubber, it lforeKisextracting necessary to leach great numbers of samples in hot water bewith acetone and benzene. The samples are held in glazed porcelain thimbles, 28 X 75 mm., with a slight taper toward the bottom. Glass wool pads are placed over the perforated bottoms of these thimbles and glass wool plugs are inserted above the samples to keep particles from floating out. Figure 1 shows an apparatus that has worked very satisfactorily for this leaching. In addition to ease of manipulation and rapidity of leaching, an advantage is that the entire thimble is surrounded by hot water, which is important when leaching is slow.
bles. (For some types of material, gravity flow might be sufficient without vacuum.) Some method must be provided to keep the vacuum from going above the equivalent head between the water level in the sump and the bottom of the box; otherwise water will be sucked back into the box and into the vacuum system. The authors use an automatic vacuum system set so as tdshut off just before the vacuum reaches this equivalent head, but an ordinary aspirator filter pump could be used with a mercury trap that would not allow the vacuum to go above the equivalent head.
To check whether water is passing through thimbles or not, water is shut off and vacuum left on. As soon as the water reaches
A two-compartment water- and air-tight box, made of wood that does not warp in contact with water, is built with the top compartment open. The partition between the top and bottom compartments is 2 inches thick. I n this partition, holes of a little greater diameter than the thimbles (depending upon the thickness of the gaskets to be used) are drilled 1.25 inches deep with the bottoms sloping toward the centers of the bottoms. I n the centers of the larger holes 0.125-inch holes are drilled the rest of the way through the partition. The sides of the larger holes are then lined with rubber gaskets. Boxes can be made to hold any number of thimbles. Those used by the authors have a capacity of 20 thimbles each. The box is connected with a vacuum line leading from the top and with a tail pipe leading from the bottom of the lower compartment. Kater is admitted to the upper compartment by means of an inlet provided with a float valve. (If hot water is used it is desirable to have an automatic water heater.) The tail pipe should extend a t least 5 feet below the bottom of box into a sump when vacuum of not more than 5 inches is used, and its lower end must be immersed in water. If noiv the thimbles whose contents are to be leached are placed in the box, and water is turned on in the top compartment and vacuum in the lower, water will be sucked through the thim1 Present address, Tung-Oil Investigations. Bureau of Agricultural and Industrial Chemistrv, E. 5. Department of Agriculture, Bogalusa, LE.
Figure 1.
General Construction
of Leaching Box
809
OCTOBER 1947 the level of the top of a thimble, the water level within that thimble should drop faster than that without. If the water used for leaching contains enough mineral matter to interfere with later steps, it can be removed by cutting off the water a t the end of leaching and pouring distilled water through the thimbles as many time; as necessary. If water pours into the box from above, it is best to have it pour into a compartment a t one end, which also contains the leveling device and is separated from the rest of the box by a partition which extends n-ithin a fraction of an inch of the partition between upper and lower compartments. This is to prevent the turbulence of the entering water from dislodging glass plugs or particles of samples from thimbles. Between the acetone and benzene extractions it is necessary to
free the thimbles of acetone. At this stage the samples are very sensitive to heat and it has been found best to remove the acetone by sucking air through them a t room temperature. By cutting the water supply off, the same equipment can be used for freeing the thimbles of acetone. For this purpose the vacuum system will have to have a greater capacity than is needed for leaching, and the tail pipe and vacuum regulator are not necessary. ACKYOWLEDGMEYT
Credit is due to E. A. Meldrum of the Emergency Rubber Prop ect for perfecting the details of construction and for constructing the apparatus used. RECEIVED June 2 4 , 1946.
Routine Method for Determining Selenium in Horticultural Materials JUSTIN S. RICNULTY, Battelle Memorial Znstitute, C o l u m b u s , Ohio ERCHLORIC acid and a vanadium catalyst are used with nitric ‘acid and sulfuric acid to destroy seleniferous organic matter. Selenium is distilled with hydrobromic acid from the digested sample into the vessel wherein it is titrated by a modified XorrisFay procedure. Greater recovery and less working time per analysis have been observed with this than with previous methods. Numerous investigators have written (1, 3, 4, 7 , 8, 11) and reviewed (6) papers on various means of converting organic to inorganic selenium, isolating it, and determining the quantity present. The first of these steps was improved in this laboratory, by devising a continuous digestion xvhich required less attention than digestions in common use. Smith (12) has described his own and Kahanes’ extensive work with perchloric, nitric, and sulfuric acids and various catalysts to destroy organic matter rapidly and retain inorganic constituents. Hoffman and Lundell ( 2 ) showed that selenium was incompletely distilled, with 15 ml. of hydrobromic acid, from mixtures in which perchloric acid.predominated. DISCUSSION
I t was found in this laboratory that, after 10 grama or less of vegetation were digeSted with 5 ml. of 60Y0 perchloric, 50 ml. of concentrated sulfuric, and 75 ml. of concentrated nitric acids a t a temperature not exceeding 210’ C., the perchloric acid remaining permitted complete recovery of added selenium on distillation with 15 ml. of 48% hydrobromic acid (Table I). The high concentration of organic matter in pot soils (one part manure, one part peat, two parts native soil, and one part sand) interfered Tvith the recovery of added selenium by the Robinson et al. (8) procedure. A vanadium-catalyzed sulfuric-nitric-perchloric acid digestion, however, enabled the recoveries shown in Table I. Using these same investigators’ (8) method for evaporating solutions, the present distillation and titration were adapted to nutrient salt solutions.
Table I.
Recovery of Selenium Added to Organic )latter
Type of Organic M a t t e r Alfalfa meal
Pot soil
Selenium Added, P.p.m.
2.0 4.0 5.0 8.0 15.0 50.0
,50.0
S e t Selenium Recovered, P.p.m. 50.8 101 250 250 248 330 1.9 3 5 5 1 7.9 15 1 49.4 50.1
The proposed distillation procedure resembles Hoffman and Lundell’s ( 2 ) . A hydrazine sulfate solution, in which the distillate is received, serves to suppress bromine and selenious acid until bromide and hydrogen attain sufficient magnitude t o keep HSe04- insignificantly small in the system (10):
Coleman and McCrosky ( 1 ) discussed the application of this relationship in preventing the conversion of selenium to the hexavalent state, preceding a Norris-Fay titration. In the present method, the Norris-Fay reaction
+
+ 4HBr +
4?\Ta2s203 H2Se03
+ iSa2SaOe + 3H20 + 4NaBr
Na2SeS406
proceeds simultaneously with the reaction 32HI
+ 8Hk3e03
--.f
321
+ Sea + 24H10
The small quantity of potassium iodide recommended in the present procedure pi favors a sharp starch-iodine end point but limits the second r e a c t i o n As a result, only a tint of suspended selenium and a trace of elemental i o d i n e a r e produced. The iodine eliminates the usual back-titration. The elimination ot transfers between the distillation and the titration, the h j drolyeis of seFigure 1. Digestion Flask and lenium t e t r a b r oDistillation Head mide before contact with the atmosphere, and the degradation of natural selenium compounds (6) incompletely oxidized by nitric acid are factors which largely account for the higher selenium values frequently obtained with the present method than with methods nom in general use. The apparatus, shown in Figure 1, combines features of Scherrer’s (9) and Pavlish and Silvrrthorn’s ( 7 ) apparatus. The
