On Tr'tbaxle Phosphoric Acid. I s '.' 



water and washed out. The residue was dried, and together 

 with the filter- ash fused again with three parts of the above- 

 named mixture for one halt-hour over the blast lamp. The 

 filtrate from the second fusion contained no phosphoric acid, 

 showing that the separation, or rather decomposition, as far as 

 it goes, will take place at a comparatively low temperature, 

 and in a short time. In this case and in the other analyses of 

 iron ores, of which I made a great number, it was almost im- 

 possible to wash out the sesquioxide of iron so that it should 

 not run through the filter. The cause of this is the above-men- 

 tioned sandy hydrate (probably very pure). In evaporating 

 the filtrate however, the concentration of the solution will 

 predispose either the alkali or the water to combine with the 

 sescpaioxide again, whereby it is rendered voluminous, and may 

 be washed out without trouble. I have already mentioned that 

 it is very difficult to separate the iron from the filter; the latter 

 has to be treated therefore with IIC1, and sometimes even with a 

 little KO, CIO.. Filtering off the solution and boiling it for 

 hours with renewed addition of KO, C10 5 , will not completely 

 destroy the organic matter, which will hold iron in solution, as 

 may be seen from the results of the analyses. The sesquioxide 

 of iron, precipitated from solutions containing organic matter, 

 looks black after ignition, and becomes heavier and of a lighter 

 color after long-continued heating in the air. The filtrate con rain- 

 ing P0 5 was evaporated and acidulated; ammonia was added, 

 and by these means it remained clear and was precipitated in 

 the usual way. 



The water in these cases was determined di recti v. The 

 results are as follows : 



