Longitudinally water-tight cables

DETAILED DESCRIPTION We claim: 1.
In a longitudinally water-tight communication cable structure having at least one signal-carrying element therein and a jacket for closing the interior of such structure off from the outside and having in its interior a filling material containing a water-repellent substance and relatively small-diameter gas bubbles embedded in such filling material, the improvement wherein: said filling material contains a reticulating thixotropic substance characterized by a 3-dimensional network-like structure formed by hydrogen bridges and which is disruptable under mechanical influence and is regenerable over a time span in a motionless state, with a significant increase of viscosity, said thixotropic substance being an oxide selected from the group consisting of B.
sub.
2 O.
sub.
3, P.
sub.
2 O.
sub.
5 and GeO.
sub.
2, and being compounded with water; and said gas bubbles being of a size relative to the resistance to disruption of said network-like structure so that the buoyancy of such gas bubbles in said filling material is significantly below the resistance to disruption in the motionless state of the filling material so that such relatively small diameter gas bubbles are maintained at their respective positions in said filling material in a time-stable manner during a motionless state.
2.
In a cable as defined in claim 1 wherein said water-repellant substance is characterized by a viscosity which substantially prevents said gas bubbles from effectuating an inadmissably large migration movement during those time spans when the network-like structure of said thixotropic substance is disrupted.
3.
In a cable as defined in claim 2 wherein migration movements of said gas bubbles are maintained below about 1 mm per 30 years.
4.
In a cable as defined in claim 1 wherein said filling material has a specific electrical resistance at 20.
degree.
C.
above about 10.
sup.
13 .
OMEGA.
cm and at 100.
degree.
C.
above about 3.
multidot.
10.
sup.
10 .
OMEGA.
cm.
5.
In a cable as defined in claim 1 wherein said thixotropic substance is present in said filling material in an amount equal to about 20% by weight, based on a 100% weight basis of said filling material