This　paper　presents　a　new　air－tight　test　for　fuel－tanks　of　motor cars．The　test　methodology　is　based　on　the　optimal pred1ction　theory，The　method　featuτes　two　points＝（i）An　additional　reference－tank　ls　comected　to　a　tank　under　test in order to yield a diffrential pressure，and this enabled the efficient sensing of the slight change of the pressure.（ii）During the　predicting　Process, two　separate　system-functions　afe　prepared　to　predict　the　time－pressure　behavior　precisdy・The　experiments　show　that　this　method is　capable　of　detecting　a　small　leak（4ml/min　appro．〉of　a　tank（volume 21l） with　good　reliability.

A drop ball machine with variable weight ball was applied for determining the impact sensitivity of oxidizer-combustible mixtures. The observed sensitivities were able to be expressed by the energy (E₅₀) of the 50% explosion height, by using correlations between both E₅₀ of the drop ball and drop hammar tests, the sensitivity order of many oxidizer mixtures was obtained and tabulated. Red phosphorus gives the most sensitive mixture with oxidizers a~nong the combustibles including red phosphorus, sulphur, ethylene giycol, aluminium, magnesil~m and tetraar~enic tetrasulfide.