Stability of the Cupric-Ammonia Color System J. P. MEHLIG, Oregon State College, Corvallis, Ore.
I
N DISCUSSING the colorimetric determination of copper with ammonia Yoe (3) has stated that if the standards are kept in a cool place away from direct sunlight they will be unchanged for a long time. Snell (8)has recommended that the standards be renewed once a month, since, although they do not fade in the light, the ammonium hydroxide acts on the glass to form a flocculent precipitate. I n a spectrophotometric study of this method the writer ( I ) found that there was no evidence whatever of fading or other change in color of the system over a period of 6 weeks.
bottles in diffuse light. Spectral transmission curves were then made with the recording photoelectric spectrophotometer a t Purdue University and when compared with t h e curves given by the corresponding freshly prepared solutions, were found to be practically identical. From the transmittancy a t 620 mp, the wave length of maximum absorption, the percentage error in the apparent concentration of copper was calculated (1) by use of the special color slide rule. The results, which are given in Table I, show that the color of the cupric-ammonia system is practically unchanged after a period of 57 weeks. Any action of ammonia on the glass is negligible when Pyrex containers are used.
TABLEI. STABILITY OF COLOR (1.961-cm. oell) Concentration of Copper P. p . m. 40 80
120 200 400 600
Transmittancy at 620 mp Fresh solution Old solution
Apparent Change
in Concentration of Copper
Acknowledgment The writer wishes to thank AI. G. Mellon of Purdue University, in whose laboratory this work was done, for the privilege of using the Purdue spectrophotometer.
%
%
%
84.3 71.0 59.7 42.7 18.0 7.7
84.0
+2.0
71.5
59.9 42.7 18.1 7.9
-2.0 -0.6 0.0 -0.3 -1.0
Literature Cited (1) Mehlig, J. P., IND.ENQ.CHEM.,ANAL.ED.,13, 533 (1941). (2) Snell, F. D., and C. T., “Colorimetric Methods of Analysis”, Vol. I, p. 145, New York, D.Van Nostrand Co., 1936. (3) Yoe, J. H., “Photometric Chemical Analysis”, Vol. I, p. 176, New York, John Wiley & Sons, 1928.
For the purpose of further study the six solutions which had been used in this test, containing 40, 80, 120, 200, 400, and 600 p. p. m. of copper in 3 M ammonium hydroxide, were allowed to stand 51 weeks longer in glass-stoppered Pyrex
A Simple Large-Capacity Extraction Apparatus EDWARD SMALLWOOD Naval Gun Factory, Washington, D. C.
A
N APPARATUS for extracting large quantities of mate-
rial exceeding the capacity of the usual laboratory extractors can be readily improvised from parts available in any analytical laboratory, and assembled as shown in Figure 1: 1. Three-neck flask 2. Bell jar 3. Desiccator cover t o fit bell jar 4. Water condenser 5a. Siphon tube 5b. Vapor conduit 6. Perforated disk 7 . Cotton or glass wool 8. SSeparatory funnel 9. Electric heater
tb
The siphon tube, 5a, can be made of block tin tubing instead of glass, for this part is easily broken in assembling. FIGURE 1. EXTRACTION Filter paper is laid on the perforated disk, with cotton or glass APPARATVS wool below it to prevent loose particles of the material from being carried into the flask. If the ground surfaces of the bell jar and desiccator top are properly ground, no lubricant is required to seal this joint. Where a lubricant is needed, one immiscible with the solvent should be applied. 903
