NUCLEONICS DATA SHEET No. 7 
SPOT-TEST setup for electrographic and 
colorimetric tests 
Preparation and Properties of Reagents 
Electrolytes 
Acetic acid: 10%- and 5%-by-volume solution in water 
Nitric acid: 0.1N, 1N, and 8N solutions 
Potassium nitrate: 10%-by-weight solution in water 
Potassium sulfate: 5%-by-weight solution in water 
Indicators* 
Cacotheline (saturated aqueous solution): Reacts with acidic stannous solutions 
to produce violet color. Other reducing ions, solutions, or compounds should 
be absent to assure specific test. Certain oxides and ions also interfere, e.g., 
colored metallic ions (arsenic, antimony, molybdenum, and uranium) 
Dimethylglyoxime (1% by weight in ethyl alcohol): In neutral or acetic acid 
solutions, produces red color with nickel. Large amounts of oxidizing sub- 
stances and iron and copper may interfere 
Diphenylearbazide (1% by weight in ethyl alcohol): Gives violet to blue color with 
mercury in weakly acid solutions. Chlorides and iron, copper, and nickel inter- 
fere in neutral or weakly acid solutions. In 8N nitric acid, test is specific but 
sensitivity is greatly reduced. Also gives violet color with molybdenum. 
Should be made up fresh each day 
o-Tolidine solution (0.1 gm o-tolidine and 0.5 gm ammonium thiocyanate in 5 ml 
acetone): Blue color with copper and red-brown with iron. Mercury and 
strongly oxidizing metal salts interfere. Should be made up fresh each day 
p-Dimethylaminobenzylidenerhodanine (saturated solution in ethyl alcohol): 
Red-violet with mercury. Large amounts of chloride interfere. Copper may 
interfere with test in neutral or acetate-buffered solutions 
Potassium thiocyanate (10% by weight in water): When used with 8%-by-volume 
hydrochloric acid solution and 25%-by-weight solution of sodium thiosulfate 
in water, gives pink to deep red with molybdenum. If solutions are added 
slowly with moderate time lapse between additions, blue color may develop. 
Mercury and other metals or compounds that consume thiocyanate interfere. 
Certain acids form complexes with molybdates and interfere 
Potassium ferrocyanide (3% by weight in water): Blue with iron and red-brown 
with uranium; test for one is interfered with by other. Copper and other 
metals that form colored compounds with ferrocyanide also interfere. Strong 
reducing agents turn iron compound white 
Potassium iodide (10% by weight in water): Gives yellow color with lead. Mer- 
cury, copper, tin, and any material that produces free iodine interfere. Indi- 
cator solution should be colorless 
Rubeanic acid (dithio-oxamide) (0.5 gm in 100 ml of ethyl alcohol; of this solution, 
5 ml are diluted to 100 ml with water): Gives olive-green to black spot with 
copper. Nickel interferes 
Quinalizarin solution (saturated ethyl alcohol solution): Gives blue color with 
magnesium, Aluminum may interfere if alkali concentration is not sufficient 
* For information on sensitivities of indicators, and interfering ions, compounds, etc., 
see bibliography references. 
208 
Chemistry 
Simple Spot Tests for 
Aluminum Contaminants 
By H. S. HILBORN and R. C. PUGH 
Pile Materials Division, Technical Division, Savannah River Laboratory 
E.I.du Pont de Nemours & Company, Augusta, Georgia 
SINcE corrosion of aluminum com- 
ponents in a nuclear reactor may be 
dangerous and expensive, it is essential 
that harmful inclusions be identified 
and traced to their source. The tests 
reported here for impurities in alumi- 
num combine electrographic sampling 
(1-4) and colorimetric spot tests (4). 
Colorimetric spot tests, well estab- 
lished methods for qualitative analysis, 
are now a recognized field in micro- 
chemistry. Feigl (5) lists over 200 
spot tests for over 40 metals, including 
rare-earth elements. Electrographic 
sampling is a spot-testing innovation; 
it has been applied recently (1-4) 
to identifying both metallic and non- 
metallic constituents in alloys. 
The reagents required for the tests 
described here are, in most instances, 
those described by Feigl. The equip- 
ment, consisting of clips, wire, 6-volt 
dry cell, cathodes, and filter paper, 
is compact and portable. Tests are 
easy and convenient, facilitating in- 
spection in the field. For information 
on indicator sensitivities, interfering 
ions, etc., see references. 
BIBLIOGRAPHY 
1. E. R. Caley, Museum News 16, No. 5, 9 (1937) 
2. M. 8. Hunter, J. R. Churchill, R. B. Mears. 
Electrographic methods of surface analysis. 
Metal Progr. 42, 1070 (1942) 
8. American Society for Testing Materials, 
symposium on Rapid Methods for the Iden- 
tification of Metals (S.T.P. No. 98) 
4. R. Jirkovsky, Chem. Abstracts 25, 5640 (1931) 
5. F. Feigl, ‘Spot Tests,” 4th. ed., vol. 1 (Elsevier 
Publishing Co., New York, 1954) 
6. M. H. Brown, W. W. Binger, R. H. Brown. 
Mercury and Its Compounds—a Corrosion 
Hazard, Corrosion 8, 155 (1952) 
7. J. R. Churchill, Mercury and Its Com- 
pounds—a Corrosion Hazard, Corrosion 8, 
430 (1952) 
