IKDUSTRIAL AKD ENGINEERING CHEMISTRY
344
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.
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
VOL. 12. NO. 6
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
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
