Patent.
3,389,259; 3,391,975; 3,407,017; 3,393,034; 3,410,624; 3,411,007; 3,412,252; 3,412,255; 3,412,256; 3,413,464; 3,414,344; 3,414,348; 3,414,725; 3,415,588; 3,415,591; 3,415,593; 3,415,994; 3,415,998; 3,416,864; 3,415,966; 3,418,037; 3,418,038; 3,418,039; 3,418,040; 3,418,119; 3,419,331; 3,419,403; 3,419,438.