Patents.
3,381,135; 3,386,332; 3,387,134; 3,391,279; 3,392,282; 3,437,819; 3,437,822; 3,506,332; 3,521,943; 3,523,719; 3,523,720; 3,524,145; 3,525,565; 3,526,446; 3,526,451; 3,527,230; 3,527,535; 3,528,724; 3,529,885; 3,529,886; 3,530,325; 3,531,183; 3,532,417; 3,532,426; 3,535,507; 3,536,377; 3,537,771; 3,538,333; 3,539,244; 3,544,190; 3,544,197; 3,545,842; 3,545,844; 3,545,845; 3,547,523; 3,548,195; 3,549,235; 3,549,239; 3,549,241; 3,549,242; 3,551,026; 3,552,824; 3,554,634; 3,558,877; 3,558,898.