The measurements of density, velocity of ultrasonic longitudinal waves at frequency of 2.5 MHz, and dynamic elastic modulus were made for raw and demineralized bituminous coals. The samples were demineralized by treatment with hydrochloric acid. It was confirmed that the demineralization by HCl was not a conservative process because it caused mot only the removal of a part of the mineral matter but also changes in elastic properties of pure coal substance.