Many physical properties can aid in identification of a substance. These may include freezing point, melting point, texture as a solid, color, reaction with other known substances, solubility in water, ethanol, acetone, and/or benzene, odor, solubility in acid and in base, and density or displacement.
Mixing unknown chemicals can be dangerous, which is why chemists and physicists often perform HPLC/GCMS on an unknown substance before subjecting it to rigorous testing using the methods described above. However, before HPLC/GCMS, all the properties listed above were used to understand the properties of an unknown sample in order to classify it properly. Density, heat, cold, reaction in water, and odor are the easiest to perform and the least likely to cause damage to the investigator.