On Tribasic Phosphoric Acid. 19] 



in the methods. And as I gave my views concerning those 

 errors, in describing the way according to which I have con- 

 ducted the analyses, I have now only to fjive some figures that 

 av i 1 1 further illustrate the incorrectness of the figures that re- 

 present the phosphoric acid, determined by the fusing method, 

 as generally conducted. 



1.7715 gr. of substance was heated for one half-hour with 11 

 gr. 'of carbonate and nitrate of soda, over a Bunsen bnrner, and 

 afterwards fused for one half-hour over a blast-lain]). After 

 complete washing out, the residue was dissolved in hydrochlo- 

 ric acid, reduced by bisulphite of soda, and the fluid boiled 

 till all sulphurous acid was driven off. Acetate of soda, and 

 then chlorine water, were added. The small red precipitate 

 was filtered out without washing, dissolved in IIC1, and pre- 

 cipitated with ]\ T II 3 . This latter precipitate was washed seve- 

 ral times with hot water, then dissolved in nitric acid, and 

 heated with molybdic acid solution. It gave 1.029 p. c. PO„ 

 as was to be expected from comparison of the analyses. In 

 the same way were conducted many analyses of different ses- 

 quioxides of iron, which were obtained from iron ores by the 

 ordinary fusing method (as basic acetates), and which inva- 

 riably were found to contain phosphoric acid. 



I will cite only two more instances, concerning the determina- 

 tion of phosphoric acid in sescpiioxide of iron — which sesqui- 

 oxide was procured from Dr. Endemann. 



Dr. Endemann found in one case 0.01 p. c. I'< >, in the ore, 

 while 0.81 p. c. was left in the sesquioxyd, as determined by 

 myself. 



In the other he found a trace only of P0 6 , while 0.13 p. c. 

 was left. 



After deciding this point, I proposed to prove that, by the 

 silica method, all the phosphoric acid can be separated from the 

 iron. A quantity of the material was fused to this end, with 

 the silicic acid mixture. 



The residue was, after washing out, prepared for the treatment 



