Patents.
3,183,763; 3,429,635; 3,433,553; 3,438,691; 3,438,692; 3,446,557; 3,447,857; 3,447,875; 3,457,000; 3,472,595; 3,474 280; 3,479,111; 3,479,118; 3,487,215; 3,486,829; 3,487,216; 3,487,227; 3,488,122; 3,488,124; 3,488,491; 3,488,503; 3,489,481; 3,492,596; 3,493,290; 3,493,752; 3,495,910; 3,497,696; 3,497,697.