ANALYTICAL EDITION
JUNE 15, 1940
of which should be brazed rather than soldered. The solution should be protected from carbon dioxide and ammonia by an absorption train, preferably a n acid and a n alkali in solution, as dry reagents tend to absorb moisture. Loss OF BORONDURING IGNITIOK. The addition of an alkali before ignition appears to be necessary in the case of certain samples, as, for instance, the dry strawberry fruit (Sample L-701). In a n experiment similar to that reported in Table 11,but in the absence of calcium oxide, the recovery of added boron was only 84 per cent. Dodd (3)reported that boron is lost, even in the presence of alkali, when fatty substances are ignited, and suggested that the fat be extracted with ether or benzene prior to ignition. This procedure was tried in the case of sunflower seeds with results that tend to support Dodd’s findings, although the indicated loss mas small.
343
Suinmarv The electrometric titration method has been adapted to the determination of boron in plant material. It is particularly suited to low concentrations found in boron deficiency studies -e. g., in the range below 50 mg. of boron per kilogram of dry material.
Literature Cited (1) Am. Pub. Health Assoc., “Standard Methods for Examination of Water and Sewage”, 8th ed., pp. 30-3, 1936. (2) Brandenburg, E., Phytopath. Z., 3, 499-517 (1!331). (3) Dodd, A. S.,Analyst, 54, 716-25 (1929). ( 4 ) Kelley, W. P., and Brown, 9. hl., Hilgardia, 3, 445-58 (1928). ( 5 ) McMurtrey, J. E., Jr., J . Am. SOC.Agron., 27, 271-3 (1935). (6) Warington, K . , Ann. Botany. 37, 630-70 (1923). (7) Wilcox, L. V., IND. ENG.CHEM.,-4nal. Ed., 2, 358-61 (1930). (8) Ibid., 4, 38-9 (1932).
Rapid Determination of Copper By a-Benzoin Oxime in Ferromolybdenum, Calcium Molybdate, Etc. LOUIS SILVERMAN, 5559 Hobart St., Pittsburgh, Penna.
F
E I G L (3) introduced a-benzoin oxime, Cd%.C(SOH).CHOH.C&, as a specific reagent for copper in ammoniacal solution. He suggested that the compound formed v-as one of new structure in which the principal valences of copper are connected through the oxygens of the oxime and hydroxyl groups, respectively, and the coordinate valences are attached to the phenyl groups. Azzalin (I), however, found (1) that for direct weighing procedures excess reagent could not easily be washed away; (2) that for ignition procedures only slow and careful ignition would remove all carbon; and (3) that in the presence of other elements the precipitate is contaminated with these elements. Obviously, then, the final determination of the copper should be made either by electrodeposition or by the short iodide titration (2, 6, 8). The rapid determination of copper in ferromolybdenum or in molybdenum steels is thus accomplished.
Proposed Procedure PREPARATION OF SAYPLE. For analyses where silicon is also to be determined ( 6 ) ,weigh 1 gram! place in a tall 300-cc. beaker, and treat with 20 cc. of (1 2) nitric acid. After rapid action ceases, heat the beaker until solution of the sample is about complete, cool somewhat, and cautiously add 10 cc. of concentrated sulfuric acid. Place the beaker in a bumping beaker, and heat to heavy fumes of sulfuric acid. Cool, add 75 cc. of (1 4) hydrochloric acid, heat until soluble salts are dissolved, and filter at once. Wash alternately with cold (1 4) hydrochloric acid and water six times, then with hot solutions to remove iron completely. The filtrate is used for co per. ’Ct’here silicon is not required, ogtain complete solution by the above nitric acid mixture with the aid of some hydrofluoric acid. After cooling, and diluting with water, add 10 cc. of hydrochloric acid. For molybdenum steels, the nitric acid solution method may be folloR-ed by fuming with perchloric acid. After cooling, add water and hydrochloric acid. For calcium molybdate, use 25 cc. of ( 2 + 1) hydrochloric acid. For ferrotungsten, use 10 cc. of (1 + 4) nitric acid, 5 cc. of hydrochloric acid, then hydrofluoric acid dropwise t o complete solution. PRECIPITATION OF COPPER. Dilute the prepared solutions to about 150 t o 200 cc., and add a solution of 15 grams of Rochelle salt dissolved in 15 cc. of water. Add a strong solution of sodium hydroxide until the test solution is alkaline t o Congo red paper, but still acid to litmus paper. If necessary, allow t o cool to room temperature. Add ammonium hydroxide till the solution turns
+
+
+
*
blue (copper above 0.5 per cent), or until distinctly alkaline to litmus, and add about 5 cc. in excess. Add slowly, with stirring, a 2 per cent a-benzoin oxime solution (10 cc. for 0 to 0.5 per cent, 15 cc. for 0.5 to 1.5 per cent copper). Let stand about 15 minutes, filter the green precipitate on an 11-cm. No. 40 Whatman paper, and wash with warm (1 99) ammonium hydroxide solution. DETERMISATIOS OF COPPER. Return the paper and contents to the beaker and add 15 cc. of nitric acid (specific gravity 1.4) and 10 cc. of perchloric acid (60 or 70 per cent grade). Mix, heat until the nitric acid has been driven out and the perchloric acid condenses on the walls of the beaker, cool, dilute with water, and boil out the chlorine. [If desired, the short iodide titration (2, 5 , 8 ) for copper may be used instead, starting.at this point.] Add ammonium hydroxide until the solution is blue, discharge the color with nitric acid, add 4 cc. of (1 1) sulfuric acid, and plate the copper at 3 volts and 0.5 ampere.
+
+
Discussion The reasons for this particular procedure should be noted. After solution of the sample and addition of the sodium potassium tartrate, the sodium hydroxide is added until the solution is alkaline to Congo red paper but acid to litmus (pH 4 to 6). If enough caustic is added to turn litmus blue, sample KO.26789 (1.00 per cent copper) returns only a portion of the copper (0.60 per cent) even after 3 hours’ standing. Evidently the alkaline tartrate has partially removed cupric ion from solution. Again, precipitation should take place at room temperature. K h e n precipitation was made hot, the results mere low and inconsistent. It is conceivable that some of the oxime was hydrolyzed into ketone and hydroxylamine, which might reduce some cupric ions to the cuprous stage and be held in solution by the ammonia and ammonium salts. Feigl stated that there should be no ammonium salts present. I n the final determination of the copper either by electrodeposition or by titration, impurities such as excess reagent, molybdenum, nickel, manganese, iron, etc., do not interfere. I n many cases the colorimetric ammonia method could be used. The usual methods for separation of copper from ferromolybdenum require separation from the molybdenum by use of caustic (or fusion), then separation of the copper from the iron-operations which are slow and undesirable. The pro-
IKDUSTRIAL AKD ENGINEERING CHEMISTRY
344
TABLEI. COPPERDETERMINED Ferromolj bdenum No. 26789
No. 15806 No. 27534
U. S.Bureau of Standards KO.71 calcium molybdate U. 9. Bureau of Standards ferrotungsten (0.039% Cu) U. S. Bureau of Standards N o 5g cast iron (1.44% CUI U. S. Bureau of Standards No. 107 (Cu 0 0 7 4 7 310 0 687%) Calcium %olybdate
1 0 0 , 1.01% 0 73, 0.747, 0.78, 0.78% 0.10. 0.10% (7)
0.03%
1.44% 0.07, 0.08% 0.40, 0.4lYG
posed method performs the separation from other elements in only one step without excess care or labor. Results on calcium molybdate were included (Table I) to confirm those of Murray and Furman ( 7 ) . There is no change in technique. With ferrotungsten considerable manganese and iron precipitated in the alkaline solution, but aside from making the washing operation slow, no harm was done. For molybdenum steels Kar (4) first separated copper and molybdenum from the steel by thiosulfate, ignited the two oxides, dissolved the oxides, and then precipitated the copper by
VOL. 12. NO. 6
a-benzoin oxime. The proposed procedure makes the separation directly. On the other hand, this laboratory has merely attacked the steel with dilute sulfuric acid, added thiosulfate, filtered off the copper and molybdenum, fumed them in nitricperchloric acids, and electroplated the copper. The proposed method could claim no superiority over this latter method, aside from the greater solution speed in nitric acid as compared to sulfuric acid. The same may be said for high chrome-nickel (18-8 per cent) steels. The reaction as described is not hazardous.
Literature Cited (1) hzaalin. E., Ann. chim. appZ., 15, 373 (1925). IND E m . CHEM.,Anal. Ed., 10, 80 (1938). (3) Feigl, F., Ber., 56 (B), 2083 (1923). (4) Kar, H . A,, IND.Eso. CHEM.,Anal. Ed., 7, 193 (1935). (5) Lord and Demorest, “Metallurgical Analysis”, p. 202, New York, McGraw-Hill Book Co., 1916. (6) Lundell, Hoffman, and Bright, “Chemical Analysis of Steel”, p. 485, New York, John Wiley & Sons, 1931. (7) Murray and Furman, J. Am. Chem. Soc., 58, 1863 (1936). (8) Scott, “Standard Methods of Chemical dnalysis”, p. 193b, New York, D. Van Nostrand Co., 1927. (2) Crowell,
A Simplified Inoculation Procedure T. L. BLACK
AND AARON ARNOLD Nopco Laboratories, Harrison, N. J.
S
OME standard bacteriological procedures ( I , 2,s)involve
the use of inoculation with an inoculum varying from a drop to 1.0 cc. in size. There are several manipulative difficulties associated with this procedure, particularly where a large number of inoculations are to be made with a suspension of the same organism. It is possible to circumvent a number of objectionable steps by the use of a syringe as illustrated in the diagram. The size of the syringe is adjusted to the number of inoculations to be made. The authors have found that a 5-cc. resistant glass syringe has wide application. The syringe may be sterilized in a hot-air oven shortly before use. The size of the needle used may be varied in accordance with the size of the drop desired or rapidity of delivery. The authors have used a aO-gage, 7.5-cm. (3-inch) needle, which allows the operator t o drop the inoculum directly into the medium. The needle may be platinum-iridium or other alloy which may be flamed repeatedly without loss of temper before use. The syringe is clamped to a stand a t an angle of approximately 30” from the horizontal. At this angle the plunger is easily tapped or pushed to yield a drop a t a time or other required amount, such as 0.5 cc. for phenol coefficient tests, but will not move without external pressure. The needle is attached to the sterile syringe and flamed. The lip of the test tube containing the inoculum is flamed, and brought up to the needle and the inoculum is drawn into the syringe. For inoculation, the needle is inserted 2.5 to 5 cm. (1 to 2 inches) inside the test tube containing the medium t o be inoculated, the plunger is given a slight tap or push to release a drop or more of inoculum, and the test tube is withdrawn and flamed in the usual manner.
Since the inoculum in the needle is not exposed to air currents except to a very limited extent and is not subjected to the handling required when a pipet is used, the danger of contamination is reduced t o a minimum. The operator has free use of both hands throughout and the time of inoculation is decreased to a third or fourth of that required by the pipet technique.
Literature Cited (1) Ruehle, G. L. A, and Brewer, C. M., U. S. Dept. Agr., Circ. 198 (1931). (2) Snell, E. E., and Strong, F. M., IND. E m . CHEY.,Anal. Ed., 11, 346 (1939). (3) Woolley. D. I T , , J . Bid. Chem., 130, 417 (1939).
STAND
CLAMP
TEST TUBE CONTAINING MEDIA TO BE INOCULATED
4I .
4
w
