SOME TESTS for METAL IONS MAKING USE of ORGANIC DYES* HORACE M. TENNEY
AND
H. J. LONG
Greenville College, Greenville, Illinois
T
HE IDEA of testing for metallic ions by means of t e s t s o n l y those which happened to be readily availorganic dyes and other organic compounds is by no able; i. e., aluminon, amaranth, malachite green, aniline means a new one. A number of current qualitative yellow, Congo red, Clayton yellow, fluorescein, indigo analysis texts make use of a few such tests. Aluminon carmine, methylene blue, methyl orange, methyl violet, (aurin tricarboxylic acid) seems to be considered a naphthol yellow S, light green S.F., orange I, Ponceau Dimethyl- 3R, rosaniline, erythrosine, and picric acid. The metal quite satisfactory test for aluminum.' glyoxime of course has a wide use in testing for nickel. ions used were such as could be precipitated as either hyLikewise the Titan yellow test,= the Clayton yellow droxides, carhonates,or sulfates; i. e., silver, lead, mercntestBsand the p-nitrobenzeneazoresorcinol test, known rous, mercuric, cadmium, bismuth, stannous, stannic, as the "S. & 0." test,' are all being used considerably antimony, aluminnm, zinc, copper, ferrous, ferric, manto detect or confirm magnesium. Also, there is quite a ganese, calcium, barium, strontium, and magnesium. Out of the three hundred or so possible combinations long list of similar tests that have been observed but which do not seem to have come into any general use. using one dye and one cation a t a time, there were three These include: an alizarin test for aluminum; an rather distinctive color effects obtained which were ammonium dithiocarbamate test for silver; a dinitro- not found to have been observed and recorded. These resorcinol test for cobalt; an ethylene diamine test for are as follows: a fluorescein test for lead, a fluorescein cadmium; a cinchonine test for bismuth; and an an- test for silver, and a napthol yellow S test for stannous thranilic acid test for copper. tin. A more detailed description of each follows. It was with the thought of extending the list someFLUORESCEIN TEST FOR LEAD what and in the hope of finding some new and distinctive To 5 ml. of solution containing lead ions are added tests for metals where needed, that this short and by no means exhaustive study was made a t Greenville two drops of the saturated fluorescein solution in College as an honors project by a senior major student aqueous methyl alcohol. Ammonium hydroxide or sodium hydroxide is then added dropwise until prein chemistry. cipitation occurs. A pink coloration usually appears a t In general, the procedure was simple and consisted once. The pale pink- or rose-colored precipitate soon in adding a few drops of the dye solution to a 5-ml. portion of solution of the metal salt, then precipitating the settles out. If no interfering ions are present the supermetal as the hydroxide, carbonate, or sulfate. For the natant liquid usually retains the bright yellow color of hydroxides either sodium hydroxide or ammonium the fluorescein in alkaline solution. This test is senhydroxide was used, depending somewhat on how am- sitive to the extent of one part of lead nitrate to photeric the metallic hydroxides might be. In pre- five hundred parts of water in absence of other ions. cipitating the carbonates a 4 N solution of sodium car- The test is quite satisfactory even in presence of other bonate was usually employed. However, in some cases cations, provided they are not present too greatly in a N/10 solution of sodium bicarbonate was used. excess of the lead. For instance, some colored ions For the sulfates any dilute solution of sulfuric acid such as ferric or copper in appreciable quantities obscure was found satisfactory. When the dyes were sufE- the pink color. However, when present in very small ciently soluble in water, aqueous solutions were used. quantities the color may be observed. When merOtherwise, in most cases, a saturated solution of the curous ion is present it, of course, turns dark, obscuring the pink. But if the mercurous solution is very dilute dye in 50% aqueous methyl alcohol was used. the color may be observed before darkening occurs. A relatively small number of dyes was used in these In all cases the pink color seems to be adsorbed by the lead hydroxide, although in some cases i t may be* Presented before the Illinois Academy of Science, Bloomingcome obscured. In the presence of aluminum, magneton. Ill.. May 3. 1935. YO&AND HILL,J. Am. Chem. Soc.. 49,2395 (1927). sium, and antimony the pink color appears immediately ' KoLTHoFF, Biochem. Z., 185, 344 (1927); C h . Absb., 21, on the addition of the reagent; but on standmg it tends 2632 (1927). to be obscured by the other precipitates. It is rather a Bmms, J. S. African Chem. In*.. 11, 67 (1928); Chem. striking that even in the presence of some colored ions Ahstr.. 23, 1838 (1929). ' Ruroa, J. Am. Chem. Sac., 51,1456 (1929). such as cobalt and nickel the pink lead hydroxide settles
out when an excess of ammonium hydroxide is added. This is especially true in the case of cobalt. FLUORESCEIN TEST FOR SILVER
The only insoluble carbonate that seemed to adsorb any of these dyes to give a distinctive test is that of silver which also adsorbs fluorescein. The test is performed as follows: To 5 ml. of a dilute silver salt solution one or two drops of a saturated solution of fluorescein in a wateralcohol mixture are added, and then 4 N sodium carbonate solution is added drop by drop. Much care must be used in order not to add too much reagent, as an excess will destroy the color. A pink- or rose-colored precipitate settles out. The question naturally arises here whether the precipitate adsorbing the color is silver carbonate or silver hydroxide. One would naturally presume that both silver carbonate and silver hydroxide would be precipitated under these conditions. However, to attempt to precipitate silver hydroxide by the addition of an ordinary solution of sodium bydroxide or ammonium hydroxide always produces a black silver oxide very shortly. It was learned, though, that on the addition of calcium hydroxide to the silver solution containing fluorescein there seemed to be formed a colloidal suspension of silver bydroxide which had adsorbed the dye in the usual manner, imparting the pink color to the entire solution. Also, when a N/10 ammonium hydroxide solution is used a similar appearance results. In time these two gradually darken and settle out, evidently as silver oxide. This test will detect silver when it is present in one part to five hundred parts of water. This test is satisfactory even in the presence of some other metal ions singly. However, the colorless ionsmercurous, mercuric, stannous, stannic, ferrous, and some of the colored ions, such as ferric and nickel, do interfere with this test. In the main the interference is evidently due to the interfering ion reducing the silver to black, h e l y divided metallic silver. Ammonium ions in all concentrations, and alkali metals in high concentrations, seem to interfere with this test.
mercuric, and bismuth. Neither will it be of much value in the presence of the colored ions. A striking exception is seen, though, in the case of a dilute copper solution where a good orange color appears. It seems to work satisfactorily in the presence of all other ions except that some care must be exercised in those cases where a heavy precipitate is formed. However, in the case of a heavy precipitate of lead chloride the color test is quite sensitive. In the presence of manganese the color is more of a violet, while with magnesium i t is of an orchid tinge. The same test may be observed by using ammonium hydroxide or sodium carbonate, although i t seems to be more delicate in the presence of sodium bydroxide.
A NAPHTHOL YELLOW S TEST FOR STANNOUS TIN
When two or three drops of a 2% solution of naphthol yellow S are added to a stannous salt solution and sodium bydroxide is then added drop by drop, the color of the solution changes to a bright red or pink. In the absence of other cations this test is sensitive in solution containing one part of stannous ion to two thousand parts of water. However, in the more dilute solutions it is always advisable to compare the solution with a blank, otherwise the slight color change cannot be detected. It should be noted that this test is not based upon the adsorption of the dye by a precipitate as in the two fluorescein tests which have been described. Obviously, this test would be of no value in the presence of metals whose hydroxides are easily reduced to the colloidal metallic state by the sodium stannite present. This is true in such cases as silver, mercurous,
STILLFOR THE PREPARATION 01.BRANDY Wood-cut from the Corlum Philosophorum, seu Liber de Secrelis Naturee (Heaven of the Philosophers, or Book of the Secrets of Nature) of Philip Ulstadius. Leiden. 1572.
