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IIIGH-SCHOOL CHE1IISTRY
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Simple Tests Identify White Metals' Reliable in ruult, they eliminate guu.rwork by the. eye and ('an be carried ouf with inexpen.rilJt and reaJt"ly Qllailn.bk equipmml. Euenlial in J'crap recovery. they auo art u.reJul}or identification oj matuial" j/l procu.r and "torage.
HE BEST method to insure thorough recovery of T high nickel alloy scrap is segregation at the hench or machine where scrap originates. However, containers in which the scrap is collected can sometimes lose their identifying label, or otherwise be misplaced. Since many of the alloys have much the same appearance, the eye test is not a safe guide, and two materials mutually unsuited for each other's use may become mixed if this test is relied upon. Mix-ups also are apt to occur in the storage of metals in warehouse and in the shop where dissimilar materials often are used along the assemhly line. Sometimes the form and shape of these pieces are the same.
the material seems to be nonmagnetic. a more sensitive method is to balance the magnet, or the specimen, on the edge of a hench or desk and hring the specimen close to the magnet or vice versa. If the material is magnetic the halance will he upset and the movement of either the magnet or the specimen will be ohserved. Suspension of the magnet on a string and carrying the specimen up toward it will hrin& similar results. In the nitric acid test, the surface of the test piece should be dean to insure direct contact between the acid and the metal. One or two drops of concentrated acid are then applied, and after a minute or two any reaction that takes place can be ohserved. After this
TABLE I QUALITATIVS TESTS POR IDBSTU'YINC SoMS COKMON WWTB ~tBTALS AND ALLOYS
Mal"t:tic Test lUadion to Magnet
Nitric Add Test Reat:tion to Add after Rea'lion 10 Cone. Add Dilution
ColOT of Ihe Solution
Magnetic
Reacts slowly
Reacts slowly
Pale green
Magnetic· (sligbtly) Nonmagnetic
Reacts
Reacts slowly
Reacts
Mar-netic Non.magnetic Magnetic Nonmagnetict Nonmagnetic
Iron Nail Test for CoPPer
Drop Test with Cupric Chloride in Hydrochloric Add Not required
Greenish blue
No copper plates out Copper plates out
Reacts
Bluish green
Copper plates out
Not required
Reacts slowly Reacts slowly No reaction No reaction
Reacts Reacts No reaction No reaction
Brown to black Brown to black Colorless Colorless
Not required Not required Not required Not required
No reaction
No reaction
Colorless
Not required
Not required Not required Not required Copper deposits .....hen drop i' diluted No deposition of copper occurs
Not required
Material Probably Is Nickel Monel Copper-nickel alloy containing leu than 60 per cent nickel, e. I., nickel-silver Steel or cast iron "Ni·Resist" Straight chromium stainless steel Cbromium-nickel stainless steels, t· "l8-S"l
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Inconel
• While Monel is usually magnetic at room temperatures, it sometimes can appear nonmagnetic. In such cases it usually will become magnetic wbeo dipped in ice water or free:ting mi:l:ture. Or, if magnetic at room temperature, it becomes noomagoetic wheo heated or dipped in boiling water. No other common metal behaves in such fashion within this range of temperatures. "K" !.{onel is always nonmagnetic. t Normally nonmagnetic, the 18-8 type alloys may sometimes become slightly magnetic as the result of cold-working. Tbe nitric acid test in such cases becomes a more reliable method of identi6c:ation. l In some cases it may be desirable to distinguish betl'fecn stainless stecl of the 18-8 type without added molybdenum from that to l'fhicb molybdenum has bun added. This test is made by immersing the specimen in question in a solution in water of 75 pu cent by weight of ortho-phosphoric: add and 1 to 30 g. per liter of common salt at 140° to 200 o P. If molybdenum is not prescnt bubbles of hydrogen will begin to form within 30 seconds. If molyb.denum is present bubbles will not form.
There are four simple identification tests which can be carried out with the aid of inexpensive and readily availahle supplies. These are the magnetic test, the nitric acid test. the test for copper with an iron or steel nail, and a test with the use of cupric chloride solution. Behavior of eight familiar metals under each of these tests is indicated in Tahle 1. Methods for carrying them out are almost as simple as the equipment required. In the magnetic test, the magnet should not he brought into contact with the specimen, care having been taken that no magnetic material such as iron or steel is beneath, or in the immediate vicinity of the specimen. The magnet will or will not be attracted to the specimen. When in doubt, and especially where I
Reprinted, with permission, from Inco.
reaction has heen noted, the acid should be diluted with three or four drops of water, one drop at a time. Should the solution turn either green or hlue, the third, or so-called "nail test," should be used. A clean iron or steel nail is rubbed in the acid solution on the metal surface, the nail being kept in contact with the specimen. If the alloy contains copper, there will be a deposition of copper either on the nail, or on the surface of the metal under the acid solution. Finally, a drop or two of additional water should he added as the nail is rubhed around to prevent the deposited copper from redissolving the acid. Chief value of the fourth test is to distinguish Inconel from the 18 per cent chrome-8 per cent nickel type of stainless steel. In this test a drop of cupric chloride in hydrochloric acid (10 g. of CuC!, in 100 mi. conc. HC1) should he applied to the cleaned metal surface 442
and allowed to remain for two minutes. At the end of this period, three or four drops of distilled water should be added slowly, one drop at a time, to the solution on the metal. The solution may then be washed off. If the sample is 18-8 stainless steel, the copper in
the cupric chloride solution will be deposited on the metal surface, appearing as a copper-colored spot. If the sample is Inconel there will be no deposition of copper. Only a white spot will be left to indicate where the testing solution was applied.
