April, 1945
ANALYTICAL EDITION
the well. If a t any future time, however, there is evidence that contamination has occurred, it is not necessary to reattach the the pump to bulb A . The barometer tube is merely loosened from its mounting, cleansed from white lacquer with acetone on cloth, heated thoroughly, and inclined again to force the new vapors into bulb A . The subsequent operations of return of mercury, trapping of capillary segment, etc., follow as previously described. This time the capillary U-section of mercury wil! probably come to rest with arms a t unequal height, but the barometer should be a t correct position.
In the assembly for evacuation of distilling apparatus SP is a central vertical standpipe, a/s-inch standard iron pipe size, including three T-fittings and an elbow a t the top. The bottom end is plugged gaatight and mounted securely by flange to desk or baseboard. The several accessories are conveniently attached and
239
removed at the respective brass hose nipples in the T-fittings. The elbow fitting, 3/8 to I/,, is connected to a Hoke needle valve, whch may be employed as a simple “bleeder” or air inlet, or may be connected to a manostat not shown in the figure, F is a filter bottle containing granular solid reagent to assist in trapping reactive vapors-for example, soda-lime. T is a vapor trap consisting of a 500-ml. long-necked, round-bottomed flask with a high, short, and sturdy side stem, and central inlet tube leading to the center of the body of the vessel. The flask rests in a dry ice-alcohol bath held in a jar protected by heat insulation, such as that provided by a 1-gallon paint pail lined with mineral wool. One should take care to place the pumpmotor assembly ( P , M ) with belt and pulleys on the inside, thus minimizing hazard of injury to the hands of workers. LITERATURE CITED
(1) Zimmerli, A., IND. ENG. CEEM., ANAL.ED., 10, 283 (1938); U. S. Patent 2,075,326.
Spectrophotometric Determination of Small Amounts OF Copper Using Rubeanic A c i d E. JOHN CENTER AND ROBERT M. MACINTOSH,Battelle M e m o r i a l Institute, Columbus, O h i o A rapid accurate method for small amounts of copper, using rubeanic acid, i s described. Spectral transmittance curves for copper, nickel, cobalt, and iron i n a weak acetic acid solution with rubeanic acid are shown. Fading of the color and maximum permissible amounts of certain elements at 650 millimicrons are indicated. Transmittance vs. copper concentration curves have been prepared for wave lengths of 400 and 650 millimicrons.
R
UBEANIC acid [dithiooxamide, (NH:C.SH)t] has been employed by a number of investigators for microdetection of copper (l-t?),cobalt, nickel, and other ions (8-8,IO). Sccording to Ray (6) copper, nickel, and cobalt are qusntitatively separated in the form of an amorphous, colored precipitate from an ammoniacal solution:
Me(Cu, Xi, Co)
Feigl and Kapulitzss (3)showed that if free acetic acid were present the sensitivity of rubeanic acid to cobalt and nickel w&s greatly depressed, but that copper still gave a reaction. Allport and Skrimshire (I) used a buffered acetic acid solution and reported that copper gave an olive-green color and that lead, manganese, bismuth, tin, and zinc gave no color with the reagent. They quantitatively determined copper in organic materials. According to British Drug Houses ( 8 ) , rubeanic acid may be employed for the colorimetric determination of copper i n a solution containing 2% each of free acetic acid and ammonium acetate and 1 cc. of 0.1% alcoholic solution of the reagent in 100-ml. volume. Free mineral acid must be absent, and not more than 0.06 mg. of copper should be present. Willard and Diehl (9) report that the reagent may be used for the quantitative determination of copper at a pH of about 4 with a little gum arabic resent to stabilize the system. They state that manganese a n f c i n c do not interfere, but that cobalt and nickel give colors with the reagent. Because of the need for more complete quantitative data on the copper-rubeanic acid complex during the analysis of potable water, the following study was made.
EXPERIMENTAL
A spectral transmittance curve of the copper-rubeanic acid complex in a weak acetic acid solution (pH 4.8) is indicated in Figure 1 (conditions given below). Spectral transmittance curves for iron, nickel, and cobalt in a weak acetic acid solution with rubeanic acid are shown in Figure 2. The nickel complex rapidly precipitates at the high concentration indicated. The iron color is due t o reaction with the acetate buffer. A plot of transmittance us. copper concentration a t wave lengths of 400 and 650 millimicrons is given in Figure 3. Standards for the plot were made up from a standard copper acetate solution, and run according to the method given under Procedure. Because it was anticipated that relatively large amounts of iron, nickel, and cobalt might be present in the solution being tested, a working wave length of 650 millimicrons waa selected even though the slope of the line (Figure 3) is far less favorable than a t 400 millimicrons. If no interference from elements absorbing in the blue is expected, or if their concentration is very low, the measurement should be made a t 400 millimicrons. Table I shows the maximum permissible concentration of elementa at 650 millimicrons using a Coleman 10s spectrophotometer with a 5-millimicron slit. The transmittance of the copper-rubeanic acid complex increases on standing, owing to ’precipitation. However, this 100,
I
,
,
,
,
I
WAVE LENGTH, HILUMICRCNS
Figure 1.
2.6 P.P.M. of
Copper Present as CopperRubeanic A c i d Complex
Vol. 17, No. 4
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
240
70
Y
s 60
z I
50
8a f
Io
0
2
4
6
8
10
TIME
Figure 4.
1 2
LfmjTn, YIUIMICROIS
WM I
Figure 2. Spectral Transmittance Curves for Nickel, Cobalt, and iron in Weak Acetic A c i d with Rubeanic Acid
3 1 5 6 7
8 9
10 11 12 13 14
15
16 17 18 19 20
z
Y 20
IO
P P M COPPER
Figure 3.
Transmittance vs. Concentration Curves for Copper-Rubeanic A c i d Complex
Table I. Element Xln++ Zn++ Fe+++ Fe++
MnSO4 Zn(CzHa0dz 24Hz0 Fe2(SOdr(NH+)zSO~. F e ( N H d z ( S 0 d z .6HzO
co++
?I“,’.+ + +
+
Maximum Permissible Concentration a t 650 Millimicrons, P.P.M. 6000 400
Co(NOs)z
Nit+
+ +
I8
20
22
24
26
21)
M
11.
Accuracy and Precision Cu Found
Cu Present P.p.ni.
P.p.m.
3.06 1.44 1.70 3.00 1.00 3.66 1.00 0.40 4.00 2.40 0.80 1.10 2.20 0.86 4.50 0.40 1.00 2.00 3.00 3.60
3.16 1.36 1.60 3.04 0.98 3.66 0.96 0.40 3.92 2.34
Difference P.p.m.
+0.10 -0.08 -0.10 +0.04 -0.02
0.00
-0.04 0.00 -0.08 -0.06 -0.10 -0.06 f0.04 -0.06 -0.06 0.00 -0.02 -0.04 0.00 4-0.06
0.70
1.04 2.24 0.80 4.44 0.40 0.98 1.96 3.00 3.66
NiSOl AgNOa lfno
