Abstract: The ferrous content is used to be converted from the sulfur determination(the difference between total sulphur and sulphate-sulphur).Therefore,the influence of natural sulphur,organic sulphur and other forms of sulphied matters existing in the rocks are not taken into consideration.Besides the whole process is a complicated operation needing a lot of time,costs and overlaborate procedures.Should there be considerable indissoluble or indissovable sulphate(such as barite,alumstone,gypysum)in hydrochloric acid of the rock,the measurements would be even more difficult.For this reason,the experiments of direct measurements on ferro from pyrite are carried out.In the experiments,soluble ferro(Fe₂O₃)was separated by a mixed acid with l:1 hydrochloric acid and 1:1 phosphoric acid solutions;and then the residue of which is dissolved with l:l nituic acid,and the ferrous content(FeOFeS₂)is determined from pyrite.