The New Student's Reference Work/Density
Den′sity is defined as the ratio of mass to volume. This term is so frequently misused by writers on scientific subjects, that it was considered worth while by the international congress of physicists, at Paris in 1900, to pass a resolution defining this quantity as stated above. Density and specific gravity are by no means the same, although one is proportional to the other. The specific gravity of any substance is defined as the ratio of its density to the density of water. The average density of a body is the ratio of the total mass of the body to the total volume of the body, while the density of a body at any one point is the limit which is approached by the ratio of a small mass about that point to the volume of this small mass.