The apparatus for hydrogen content measurement is HYSCAN Ⅱ made by SEVERN SCIENCE LTD., UK. RPT, a semi-quantitative technique, is used to determine the hydrogen in aluminum melts. Reduced pressure test (RPT) is also called vacuum solidification test or Straube-Pfeiffer test. A small amount of molten aluminum alloy sample is allowed to solidify under controlled reduced pressure and the gas content is estimated or determined by observing the solidification behavior of the specimen or by density measurement or porosity analysis of the solidified specimen. Measurement accuracy is 0.01ml/100g and measurement range is 0-0.99 cm/100g.