All marriages between a white person and a negro, and all marriages which are prohibited by law on account of either of the parties having a former wife or husband then living, shall be absolutely void, without any decree of divorce, or other legal process. All marriages which are prohibited by law on account of consanguinity or affinity between the parties, all marriages solemnized when either of the parties was insane, or incapable from physical causes of entering into the marriage state, shall, if solemnized within this state, be void from the time they shall be so declared by a decree of divorce or nullity, or from the time of the conviction of the parties under the third section of the 196th chapter.