for all fellow worshipers of the ultimate opiate, here's a little article i found on the web concerned with assessing purity of street heroin, so here goes the relevant extract:
Colour Tests
Marquis' reagent (Formaldehyde in concentrated or (6 + 1) H 2SO 4)1 -purple red changing to purple.
Frshde's reagent (Molybdate in concentrated H 2SO 4)2-strikes violet,quickly changing to strong purplish red, fading out to weaker brown or brownish, then developing green.
Mecke's (or Lafon's) reagent (Selenious acid in concentrated H 2SO 4)3,4- green,quickly greenish blue, changing to blue,slowly to bluish green with yellow-brown edge, then olivaceous green.
Comment on tests 1 to 3: These sulfuric acid reagents provide highly characteristic colour tests for the spot-plate, and most adulterants and diluents do not seriously interfere. Rarely, a sample may contain so little heroine that charring of the diluent sugar with the concentrated acid will obscure the colours. Of course in that case, a separation is necessary. Imperfect acetylation does not matter as morphine and monoacetylmorphine give the same colours. The initial colour with the hydrochloride is slightly different from that with the free alkaloid or sulfate, bluer with Frshde's reagent and more yellow-brown with Mecke's; and this effect is increased if additional chloride is present. Chloride or hydrochloride causes some effervescence with concentrated sulfuric acid. The inexperienced analyst should compare the colours with those yielded by known diacetylmorphine hydrochloride.
Nitric acid-light yellow solution, gradually bright green.5Concentrated HNO 3 is usually used, but a (4 + 1) acid is somewhat better (4 parts concentrated HNO 3mixed with 1 part H 2O).
Comment: This highly characteristic test is not very sensitive and often enough it may not be obtained on adulterated, diluted samples. Morphine gives an orange red color fading to yellow; sometimes with a little morphine present a red-orange is obtained at first and later the green of diacetylmorphine develops. Monoacetylmorphine is similar to morphine.
Copper test. To a little of the powder on the spot plate add several drops of water, 2 or 3 drops of 3% H 2O 2, a drop or two of NH 4OH and stir with a piece of copper. A pink to red color is produced.
Comment: The reaction was originally discovered by Deniges; the form of the test used here was introduced by Oliver.6,7 The test is given by various phenols and their acetyl derivatives including morphine and diacetylmorphine.8The stirring with copper should cause the formation of bubbles of oxygen, and in the absence of diacetylmorphine or other reactive compound the solution should gradually turn blue; if this does not occur, the peroxide solution was too weak.
Microscopic Tests
Platinum chloride, H 2PtCl 6. A little of the powder being examined is dissolved in a drop of water, or better in diluted acetic acid, on the microscpoe slide, and a drop of the 5% reagent solution is added, then crystals are looked for under the microscope. They form gradually and are needles in rosettes, like cokleburs; they form best at a dilution near the limit of amorphous precipitation. The crystals grow larger and form blades in rosettes in the presence of acetic acid, which also diminishes the interface of quinine, and may be used up to (1+1) strength. (Lews, New York International Revenue Laboratory.)
Comment: This test was probably originated by Putt in 19129; it is the best known crystal test for diacetyl-morphine, and has long been a favourite for identification. The crystals are very characteristic, but the test is much more easily spoiled by the presence of other alkaloids than either of the two following.
Mercuric iodide in HCl. (The solvent solution contains about 27% by volume of concentrated HCl, or 10% by weight of HCl, and is saturated with Hgl 2.) This reagent is applied to a little of the dry substance on the microscope slide. The crystals are branching threads and splinter-plates.10,11
Comment: The test is extremely sensitive and usually succeeds even with highly adulterated samples, though since the crystals are colourless, care must be taken to distinguish them from any undissolved particles of the powder. The reagent can also be applied to the aqueous solution.
Gold H Bromide in (2 + 3) H 2SO 4. A drop of reagent is added to a drop of aqueous solution of the substance on the microscope slide. The crystals are fine needles, mostly scattered, but often partially in sheaves or rosettes. The interference of quinine is much diminished by the presence of acetic acid. Use a very little of the powder scattered on the slide; add a drop of 20% (or stronger) acetic acid solution; do not stir, but after a moment add a drop of the reagent.11
Comment: The test is extremely sensitive, and is best obtained on a very dilute solution, containing only just enough diacetylmorphine for a light amorphous precipitate when the reagent is added. Caffeine yields somewhat similar crystals with this reagent.
Other recommended microcrystal tests for diacetyl-morphine can be made on the aqueous solution with 1:20 HAuCl 4 in (1 + 1) H 2SO 4,11 half-saturated sodium picrate, and either Na 3PO 4 or Na 2CO 3. The last mentioned reagents precipitate the free base, which soon crystallizes.
More tests have been mentioned than are really necessary. It is considered that with good results in tests 1, 2, 3, 7, and 8, the diacetylmorphine may be considered as positively identified, without the necessity of separating it from accompanying impurities, adulterants, and diluents.
the original article, with more generic info (and info on how to test for particular adulterants) can be found here:
happy testing