ANALYTICAL EDITION
180
VOl. 4, No. 2
deposition, a thick deposit does not necessarily have the same s t r u c t u r e throughout. This is illustrated in Fig-
FIGURE 6. COPPER. Top, coarse-grained; bottom, fine-gained
and 3 amp./dm.2 on -stainless steel to which it did not adhere well, and could be strimed. It was 0.35 mm. thick. The toD-iart of Figure 7 is a Dicture of the the structure of the part lastdeposited. The lines in the lower picture show a shift toward the left, a characteristic of the alpha phase as the percentage of
FIGURE 7. BRASS. Top, next to cathode; bottom, away from cathode
’
Hill, 1927.-
(3) Glocker, “Materialpruefung mit Roentgenstrahlen,” Springer, 1927.
fixed, then a photograph of a sample plated with a coating of unknomin thickness may be compared with a set of those carefully prepared from samples of known thickness to determine whether the deposit is thicker than required or not so thick. The photographs in Figure 5 also indicate that the x-ray examination itself only with the surface layer when the soft radiation from It target Of low atomic number is used. The relative grain size of electrodeposited metals may also be determined with the same camera. Figure 6 illustrates this for the case of copper electrodeposited from an ordinary acid copper sulfate bath. The top $cture shows the speckled
(4) Hull, Phw. Rev., Dl 17, 576 (1921). ( 5 ) Kerstenv Rev. SCi. Instruments,3, 145 (1932). (7) (8) (9) .,
(10)
Marc, “Die Verwendung der Roentgenstrahlen in Chemie und Technik,” Barth, 1926. Neuburger, “Roentgenographie des Eisens und seiner Legierungen,” Enke, 1928. Neuburger, "Roentgenographic der M e t a h und ihrer Le&ungen,” Enke, 1929. Schleede and Schneider, “Roentaens~ektroskopieund Kristallstrukturanalvse.” deGruvter. 1929.Trillat, “Les h p l i c a t i o n s des Rayons X,” Les Presses Universitaires de France, 1930. (1925), Westgren and Pragmen, Phil. Mag., [61
RECEIVED September 22, 1931.
Determination of Minute Amounts of Boron in Soils WILFRED
W.
SCOTT AND
SONDHEIM K. WEBB, University of Southern California, Los Angeles, Calif.
INUTE amounts of boron are essential to the normal development of such plants as the tomato, soy bean, tobacco, and others, but, on the other hand, as little as three to four parts per million by weight in the soil may have a decided toxic effect on other plants. Citrus and walnut trees are seriously affected and sometimes killed by very small amounts, hence the importance of a rapid and accurate method for the testing of soils is evident. Further reference to the effect of boron on the growth of plants will be given in a paper on the analysis of the irrigation waters of Southern California. Three representative types of methods for the determination of boron are Chapin’s modified volumetric method ( 6 , 5 ) , the gravimetric method as outlined by Gooch and Jones (S),
and the colorimetric method originated by Bertrand and Agulhon (1). Large samples of soil are necessary for the determination of small amounts of boron by either the volumetric or gravimetric methods, and not being nearly so rapid as the colorimetric method they are not recommended for the determination of minute quantities of boron in soils. The modification of the colorimetric method presented in this paper permits the determination of amounts of boron well within the limits that have an appreciable effect on plants. Tests with known amounts of boron as boron oxide, ranging from 0.005 to 1.Omg., gave fairly accurate quantitative results. The method is applicable to the determination of boron in soils, and satisfactory results may be obtained with samples of soil weighing 100 grams or less. The procedure for the
April 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
colorimetric determination as modified and recommended by the authors is as follows: REAQENTS Hydrochloric acid, sp. gr. 1.162 Phosphoric acid, 85 per cent Sodium carbonate, 1 normal Methanol, absolute Turmeric solution. Add an excess of turmeric powder to 95 per cent alcohol and filter. In place of turmeric powder, curcumin may be used, as recommended by Pope and Ross ( 4 ) . Turmeric paper. Soak a good grade of filter paper in the turmeric solution, squeeze out excess by means of a photographer's roller for mounting prints, dry, and cut into uniform strips. Standard borate solution. Dissolve 0.2739 gram of sodium tetraborate in water to make a liter of solution. One cubic centimeter of solution contains 0.1 mg. of boron oxide. APPARATUS Distillation flask of 250 cc. capacity, sup orted on water bath; flask carrying a one-hole stopper wit{ long-stem funnel of 50 cc. capacity Water-cooled condenser 40 cm. long Platinum dish of 60 cc. capacity Platinum crucible of 25 cc. capacity Glass vials 30 mm. high and 6 mm. in diameter Glass vials 60 mm. high and 12 mm. in diameter
millimeters of the red color thus produced against a series of standard papers prepared by soaking strips of turmeric paper in solution containing known amounts of boron treated in the same manner. Note. This procedure is suitable for quantities of boron oxide ranging from 0.1 to 0.005 mg. Amounts ranging from 1.0 to 0.1 mg. can be determined just as successfully by using larger vials and longer etrips of turmeric paper.
Several types of soil were used in testing the effectiveness of this method, the results of the experiments being shown in Table I. A detailed study was made first with sandy loam, and this was followed by more limited experimental work using gumbo and adobe. I n addition, samples of soil taken from a number of citrus orchards in Southern California were analyzed, with results as given in Table 11. TYPES TABLEI. BORONIN SOILSOF DIFFERENT BzOa
TYPEOF SOIL
Sandy loam
500
0.25
0.05 0.05 0.05
PREPARATION OF SAMPLE
COLORIMETRIC METHODFOR BORON To the cool residue add four drops of hydrochloric acid, sp. gr. 1.162, and 0.5 cc. of distilled water. Transfer to a vial 30 mm. high, rinsing several times with water, and dilute to 2 cc. as shown by a mark on the vial. Immerse a piece of turmeric paper (45 by 3 mm.) in the liquid to a depth of 15 mm. and allow it to soak 3 hours a t a temperature of 35" C., or 24 hours a t room temperature. (The former is preferred as it gives a more clearly defined coloration.) Compare the height in
TOTAL BrOa FOUND
VT. OF ORIGINALLY BpOs S A M P L ~ FOUND ADDED Grams Me. Mg. 100 0.05 0.0 100 0.05 0.0 200 0.11 0.0 200 0.12 0.0 500 0.25 0.0 0...5.~ 2
Dry the soil in an electric oven a t 105" C. for 24 hours, pulverize, and sift to remove foreign material. Extract 100 grams in 100 cc. of boiling water, allow to stand for about 30 minutes until settled, and then filter, catching the filtrate in a silica dish of sufficient capacity. Silty clay that is finely divided requires several hours for settling, but this may be hastened by salting. Add a small amount of sodium carbonate, evaporate the solution to about 25 cc., then transfer to a platinum dish, evaporate to dryness, and ignite the residue to destroy organic matter. Treat the cooled residue with 10 cc. of phosphoric acid and transfer the solution to the distillation flask. Rinse the platinum dish with 20 cc. of methanol in two or three portions, and transfer the portions to the flask. Distil the solution, collecting the distillate in a platinum dish of 60 cc. capacity. Add 4 to 6 drops of normal sodium carbonate solution to the distillate. About 20 minutes are required for the distillation. Add 10 cc. more of alcohol to the flask through a dropping funnel and make a second distillation, continuing it until liquid ceases to come over. With careful work, the sample being free from water, all boron will be found in the distillates. It is advisable to make a third distillation with 10 cc. of alcohol, testing a drop with turmeric paper and hydrochloric acid to be sure that no boron remains in the residue. If present, complete the distillation, adding this to the main solution. Evaporate the combined distillates on a water bath a t a temperature below boiling, carrying the evaporation to 5 cc. Transfer the solution to a 25- or 30-cc. platinum crucible, and carry the evaporation to dryness. The smaller dish is essential because the quantity of solvent subsequently used is not sufficient to remove the residue from a larger dish,
181
0.0 0.0 ~ .
Mg. 0.05
0.05 0.11 0.12 0.25 0.25
.
0.05
0.11 0.0:
TABLE11. BORONIN SOILSFROM CITRUSORCHARDSIN SOUTHERN CALIFORNIA BzOa FOUND LOCATION
ORCHARD
TYPEOF SOIL
PER
100 GRAMSOF SOIL Ma. ~~
Valencia orange Surface loam Placentia Surface loam Yolo County Lemon Root zone Yolo County Lemon Lemon Surface loam Corona Yolo County Valencia orange Surface silty clay loam Surface loam San Fernando Lemon" Root zone San Fernando Lemon a Showing slight injur)7 from boron.
0.200 0.075 0.080 0.055 0.060
0.3001 0.300
Different size samples of sandy loam were used in the testing to determine whether or not small quantities of soil could be used for accurate quantitative determinations as effectively as larger samples. The advantage of using the small quantities of soil is readily seen in that the time required for leaching and evaporating the 100-gram samples would be considerably less than that required for a kilogram sample. LITERATURE CITED (1) Bertrand and Agulhon, Bull. SOC. chim., 7,90,128 11910). (2) Chapin, J . Am. Chem. Soc., 30, 1691 (1908). (3) Gooch and Jones, Am. J . Sci., [4]7,34 (1899). (4) Pope and Ross, Am. Fertilizer, 52,66 (19130). (5) Wilcox, IND.ENO.CHEX., Anal. Ed.,2, 358 (1030). RECEIVEDAugust 12, 1930. Resubmitted October 12, 1931.
CORRECTION. E. Lieber and R. Rosen, authors of "Determination of Total Sulfur in Gases" [IND. ENQ.CHEM.,Anal. Ed., 4, 90 (1932)], wish to add the following acknowledgment to their paper: The authors appreciate the help of J. B. Lewis of this laboratory who has developed the gravimetric sulfur method and made all the analyses in connection with this work.
