3 Aug 1972; 9 p; AU PATENT DOCUMENT 426758; Available from the Commissioner of Patents, Canberra; Filed 26 Sep 1967, publ. 3 Apr 1969, priority UK 26 Sep 1966 (42956/66), 29 Nov 1966 (53492/66), 30 Mar 1967 (14684/66), copies available from the Commissioner of Patents, Canberra.