OK, second try after firefox crashed grrrr.....
The reaction of DXM with Marquis will turn a gray colour, but it has been suggested that the reaction colour can be confused with MDMA
MDMA, when in high concentrations /purity will often produce wisps of smoke with Marquis, and depending upon ambient temperature and that of the reagent (kept in fridge?) the time taken for each reaction to occur can differ. Normally DXM takes longer to react with Marquis.
Mandelin is not considered a suitable reagent for DXM
Mecke will turn a yellow colour with DXM, and a green-->blue with MDMA. For this reason mecke is considered the better reagent for indicating the presence of DXM.
A couple of other tests are listed for DXM
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From Clarkes Analysis of Drugs and Poisons
Aromaticity (Method 2)
Add two or three drops of nitric acid to the sample, heat in a water–bath at 100° for 1 min, cool the mixture, dilute three to four times with water and make the solution alkaline by the addition of a 40% (w/v) solution of sodium hydroxide.
Note: A control of cold nitric acid should also be used. Cold concentrated HNO3 is adding to the sample, and if any colour is produced it is then checked to see if it fades upon heating. A range of colours can be produced, but none of them indicate DXM. Only the alkaline method above should produce any colour with DXM; p_d
DXM (alkaline method)—yellow/orange–red
Liebermann's Test
Add 1 g of sodium or potassium nitrite to 10 mL of sulfuric acid with cooling and swirling to absorb the brown fumes.
Method
Add two or three drops of the reagent to the sample on a white tile. Occasionally it is necessary to carry out the test in a tube and heat in a water–bath at 100°. Many substances give colours with sulfuric acid alone and the test should be repeated using sulfuric acid instead of the reagent.
DXM—black.
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As DXM is a tertiary amine, it should also be identifiable using methyl iodide, although for reason of the toxicity and carcinogenicity of methyl Iodide, this is not recommended