Patents.
3,418,467; 3,437,399; 3,437,400; 3,460,887; 3,467,917; 3,469,920; 3,498,690; 3,498,698; 3,498,720; 3,499,697; 3,500,238; 3,500,452; 3,501,221; 3,501,222; 3,501,224; 3,501,223; 3,501,587; 3,501,626; 3,501,633; 3,502,393; 3,502,394; 3,503,006; 3,503,318; 3,503,666; 3,503,668; 3,503,685; 3,504,181.