Preheat oven to 375 degrees F (190 degrees C). Grease and flour two 9 inch round pans.

In top of double boiler, over hot water, melt chocolate. Set aside to cool slightly. In large mixing bowl, beat sugar and butter until light and fluffy. Add eggs, one at a time, beating well after each addition.

Stir together flour and salt, then add alternately with milk to butter mixture. Beat until well blended. Add chocolate and beat until blended. In a small cup, mix vinegar and baking soda. Stir until soda is dissolved. Add to batter and beat until blended.

Pour batter into prepared pans. Bake at 375 degrees F (190 degrees C) for 25 to 30 min or until wooden pick inserted into center of cake comes out clean. Cool 10 minutes in pan then turn out onto wire rack to cool completely.