Immersion oil containing aliphatic thio compounds

Claim 1

In the combination for immersion oil optics of an immersion oil completely filling the space between the objective lens and a preparation or a cover glass over the preparation to be optically investigated, the improvement wherein the optical immersion oil comprises one or more aliphatic thio compounds of the formula R.sup.1 O--(CH.sub.2).sub.n.sbsb.1 --S--(CH.sub.2).sub.m.sbsb.1 --OR.sup.2I wherein R 1 denotes hydrogen, benzoyl or a group --(CH 2 ) n .sbsb.2 --OR 3 and R 2 denotes hydrogen or a group --(CH 2 ) m .sbsb.2 --OR 4 , R 3 represents hydrogen or a group --(CH 2 ) n .sbsb.3 --OH and R 4 represents hydrogen or a group --(CH 2 ) m .sbsb.3 --OH, the indices n 1 , m 1 , n 2 , m 2 , n 3 and m 3 signify whole numbers of 2 to 6 and the sums n 1 +m 1 or n 2 +m 2 or n 3 +m 3 amount to at most 8, or derivatives thereof in which one or more of the methylene groups is/are substituted by alkyl groups containing 1 to 4 carbon atoms.