Determination of Molybdenum. 169 



perly conducted in an atmosphere of carbon dioxide, it was 

 shown that the iodine in the distillate may be trusted to indi- 

 cate the molybdic acid within reasonable limits of accuracy. 

 It appeared, however, that too great an excess of potassium 

 iodide tends to induce excessive reduction, and that the same 

 tendency shows when the liquid is concentrated to too low a 

 limit. 



To this criticism Friedheim took exception* and contrasted, 

 to their disadvantage, our results by the modified method with 

 those of Friedheim and Euler by the original method. It 

 became necessary, therefore, to point outf the fact that of the 

 results published by Friedheim and Euler, upon which reliance 

 was placed to prove the reliability of their method, five out of 

 seven in one series and one out of five in another series had been 

 calculated incorrectly from data given. Another series of six 

 determinations was, however, apparently faultless in this re- 

 spect. More recently:}: Euler has explained that the errors 

 were not really arithmetical. Two of them may be presumed, 

 inferentially, to be due to careless copying or proof-reading ; 

 and four, we are told by Euler, were introduced into the 

 series by mistake, and actually represent (as Prof. Friedheim 

 kindly informs him) the analysis of a sample of ammonium 

 molybdate of undetermined constitution : that is to say, the 

 figures now given by Euler represent the original percentages 

 of molybdenum trioxide which had been changed by some 

 unconscious process from 



8062 per cent to 81.85 per cent. 

 80-71 " " 81*69 " 



80-63 " " 81-67 " 



80-78 " " 81-78 " 



Curiously enough, Euler's corrected figures, as given here, are 

 still affected by trifling arithmetical errors of from one to four 

 units in the second decimal place. The agreement of these 

 results among themselves is no proof of the correctness of the 

 process of analysis. The great variation between the average 

 percentage of molybdenum trioxide in ammonium molybdate 

 as found by Euler in a molybdate of known constitution and 

 the percentage of the trioxide as found by Friedheim (if we 

 understand Euler aright) may be due conceivably to either or 

 both of two causes, viz : the change of material analyzed and 

 the change of operator or conduct of the operation. We shall 

 show in the following account of our work that the exact con- 

 trol of the conditions of treatment, along the lines laid down 



* Ber. d. d. chem. G-esell., xxix, 2981. 

 + Gooch, this Journal IY, iii, 237. 

 % Zeit. f. Anorg. Chem.. xv, 454. 



Am. Jour. Sol — Fourth Series, Yol. YI, No. 32.— August, 1898. 

 12 



