| 摘要 |
PURPOSE:To prolong a measuring time and to reduce manufacturing cost, by using ferrite particles as the sand material for an hourglass. CONSTITUTION:An hourglass 1 is made of glass and formed into such a configuration that two conical containers 2 are connected so as to be mutually communicated through fine parts (bee waist) 3 at the leading ends of two respective cones and ferrite particles are sealed in said containers 2. Each of the ferrite particles pref. has a globular shape having small projections provided to the surface thereof. The material of the ferrite particles is a divalent metal salt represented by MO.Fe2O3 (wherein M is Mn, Fe, Co, Ni, Cu, Mg or Cd) and the particle size thereof is desirably 0.02mm or more. The caliber of the bee waist 3 is set to about 0.8mm. By this method, if the same dimension is taken, a measuring time becomes long and, while at the time of the same measuring time, miniaturization is enabled and manufacturing cost can be reduced.
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