Abstract: A double tube from which a balloon catheter having a high rigidity and a low fluid resistance can be easily produced by means of an extruder or the like, an apparatus for producing the double tube, a balloon catheter produced by using the double tube, and a process for producing the balloon catheter are provided. The double tube comprises an outer tube having a lumen extending from the distal end to the proximal end, and an inner tube which is provided within the outer tube and has a lumen extending from the distal end to the proximal end, wherein a longitudinal member in the strip form is provided as a connecting member which continuously connects the inner surface of the outer tube to the outer surface of the inner tube in the axial direction. A balloon catheter can be easily produced by using this double tube.

Abstract: A magnetic powder for magnetic recording media, which has an average particle diameter of at most 0.1 .mu.m and is represented by the following general composition formula:(Fe).sub.a (Zr).sub.b (Si).sub.c (M.sup.1).sub.d (M.sup.2).sub.e (M.sup.3).sub.f (O).sub.gwherein M.sup.1 means at least one metal element selected from Ba, Sr, Ca and Pb, M.sup.2 denotes at least one metal element selected from Mo and W, M.sup.3 stands for at least one metal element selected from Mg, Ti, Mn, Ni, Cu, Zn, Sb, La, Al, In, Ce, Nd and Sm, a, b, c, d, e, f and g respectively represent the numbers of Fe, Zr, Si, M.sup.1, M.sup.2, M.sup.3 and O atoms, a is a number of 8.0 to 12.0, b is a number of 0.01 to 6.0, c is a number of 0.05 to 6.0, d is a number of 0.3 to 6.0, e is a number of 0.01 to 6.0, and f is a number of 0.0 to 6.0, and g is the number of oxygen atoms satisfying the atomic valences of the other elements.

Abstract: A magnetic powder for magnetic recording media, which has an average particle diameter of at most 0.08 .mu.m and a ratio of the maximum diameter to the maximum thickness of at most 8 and is represented by the following general composition formula:(Fe).sub.a (Sn).sub.b (Si).sub.c (M.sup.1).sub.d (M.sup.2).sub.e (M.sup.3).sub.f (O).sub.gwherein M.sup.1 means at least one metal element selected from Ba, Sr, Ca and Pb, M.sup.2 denotes at least one metal element selected from Cr, Y, Ce, Nd, Sm, Al, La and Cd, M.sup.3 stands for at least one metal element selected from Mg, Ti, Mn, Ni, Cu, Zn, Sb, In, Mo and W, a, b, c, d, e, f and g respectively represent the numbers of Fe, Sn, Si, M.sup.1, M.sup.2, M.sup.3 and O atoms, a is a number of 8.0 to 12.0, b is a number of 0.01 to 6.0, c is a number of 0.05 to 6.0, d is a number of 0.3 to 6.0, e is a number of 0.01 to 6.0, and f is a number of 0.0 to 6.0, and g is the number of oxygen atoms satisfying the atomic valences of the other elements.