WET ASSAY OF IRON". 



51 



ganate of potassa converts the protoxide of iron from 

 10 equivs. = 3'500 grms. of pure iron into sesquioxide. 



So that if 19-80 grms. of the salt be dissolved in 1 

 litre (=1000 grms. or 1000 cub. cent.) of water ; 100 

 cub. cent, of this solution will correspond to 3'50 grms. 

 of iron. It must be kept in a well-stoppered bottle. 



An equivalent quantity (say 3*5 grms., or half that 

 amount) of the ore to be tested is dissolved in concen- 

 trated hydrochloric acid, in a capacious flask, by the 

 aid of heat. If the insoluble residue of foreign mat- 

 ters, such as clay, silica, &c., be not very considerable, 

 it is unnecessary to filter the solution. The iron must 

 now be entirely reduced to the state of protoxide, either 

 by mixing the solution with several times its volume 

 of a saturated solution of sulphurous acid, and boiling 

 so long as any trace of that gas is perceptible ; or, bet- 

 ter, by allowing a piece of zinc, free from iron, to 

 remain in the liquid until its color is changed to a pale 

 green. It is then decanted from the zinc, the latter 

 thoroughly rinsed, the solution diluted with the washing- 



Fig. 6. 



Fig. 7. Fig. 8. Fig. 9. Fig. 10. 



The figures 6, 7, 8, 9, 10 represent the burette, the pipette, and the 

 graduated vessels used in volumetric analysis. 



water, and mixed with some more hydrochloric acid ; 

 the solution of permanganate of potassa is then drop- 

 ped in from a burette (see Alkalimetry), until the 



