Melt chocolate in boiling water. Cool. Cream butter and sugar until fluffy. Add egg yolks one at a time and beat well after each addition. Add melted chocolate/water mixture, and vanilla. Sift together the flour, salt and soda. Add to the above mixture alternately with the buttermilk, and beat until smooth. Gently fold in the stiffly beaten egg whites. Pour into 3 later pans, greased and floured, or use a large load pan. Bake at 350° 30 to 40 min. Cool. Remove layers from pans. Ice between each layer, and on top with coconut-pecan frosting.