Patents.
3,337,733; 3,373,380; 3,397,936;3, 399,013; 3,438,700; 3,464,027; 3,466,110; 3,474,252; 3,474,255; 3,480,367; 3,498,691; 3,498,693; 3,498,694; 3,499,153; 3,501,219; 3,502,391; 3,502,416; 3,502,874; 3,503,315; 3,503,667; 3,503,671; 3,504,975; 3,519,322; 3,519,325; 3,520,585; 3,520,586.