Differentiate between iron and copper sulphide

[Jehannum]

TL;DR Summary

Simple chemical / flame test needed to identify substance

I have a quantity of black, lustrous powder taken from inside a gas pipe.

I want to know whether it's from copper pipe or from steel pipe.

Is there a very simple test I can do? I'm not a chemist and have no specialist equipment.

 

[chemisttree]

Dissolve it in HCL. To several drops of the liquid add several drops of ammonia. If it turns blue, it contains copper. If it forms a ppt, it’s iron.

If it won’t dissolve easily, it is probably an organometallic iron compound or an iron compound with organic “stuff” coating it. In that case you would need to digest the sample with nitric acid before adding the ammonia. You need special equipment and protections to handle that.
If you want to do flame tests, you need to dissolve some of it first... either with HCl or HNO3 (nitric acid). Dissolve the sample, decant or filter and heat to boil. Reduce to a moist solid and reconstitute in a minimum of DI water. Dip a q-tip into the liquid and hold over a BLUE flame to observe the color. Iron will likely be difficult to see but copper (green-blue) is easy.

 

[jim mcnamara]

To amplify @chemisttree nice post:

HCl is hydrochloric acid, which you can get at hardware and pool supply stores.