If you have the proper equipment you could heat it up until it melts... Most adulterants will burn off at lower temperatures...
you can go by how it looks after its been melted (on foil, glass peice whatever). if its pure it will re-crystalize right away and will look like shards of glass (long). if it re-crystalizes back into pinwheel looking patterns then it means it was under-reduced... and prolly about 60-80% pure... and if it dont re-cyrstalize and stays gooey or some nasty shit, then thats what it is... shit.
Crystallography is inaccurate as some common cuts such as dimethylsulfone will not affect the crystalization much. Melting point testing would be easy but some common cuts do not affect the melting point much. TLC is easy. HPLC/GCMS are harder and require equipment, but are the best way to go. NMR or IR spectroscopy would be a good alternative. Conclusion: There is no easy way that will be accurate. Any method that can also be used for quantification (measuring % purity) will be expensive and hard to obtain. Make friends with a student that can get unrestricted access to professional chromatography or spectroscopy equipment.
Melt point. Get an infrared thermometor and a torch and a glass vessel. If memory serves, 175 C is melt point. If melting begins within 5-10 degrees of ideal melt point, you're around 90%
