T, M. Chatard cm iiew Analytical Methods. 



Art. LX. — Contributions to Chemistry from the Laboratory of the 

 Lawrence Scientific School. No. 15. — On some 7iew Analytical 

 Methods ; \>j Thomas M. Chatard. 



§ 1. On the Determination of Molybdic Acid as Plumbic Molybdate. 



Great difficulty has always been experienced in determining 

 molybdenum by any of the methods generally in use. The 

 precipitation as mercurous molybdate, and the subsequent treat- 

 ment, are both tedious and unsatisfactory, and an accurate de- 

 termination as sulphide is almost impossible, the filtrate remain- 

 ing blue even after repeatedly passing sulphydric acid and 

 filtering. 



The following method will, I hope, be found to give satisfac- 

 tion, both as to ease of working and accuracy of results. 



Add to the boiling solution of the molybdate, plumbic acetate 

 in slight excess. Boil for a few minutes ; the precipitate, at 

 first milky, will become granular and will subside easily, leav- 

 ing a perfectly clear supernatant liquid. Care must be taken iii 

 boiling, as the thick milky fluid is very apt to boil over. A 

 ribbed filter is to be used and the precipitate is to be washed 

 with hot water. The washing proceeds with great ease and thor- 

 oughness, and not the slightest milkiness should be apparent in 

 the filtrate. The precipitate is dried at 100°. separated fi-om 



: 46-60 " " 



1.2221 " « » " 2-1811 " « =46-66 " " 



1-2H71 " " " « 2-2999 " " =46-74 " " 



Mean = 46-66. 



The theoretical percentage of Mo in Na^MoO, is 46-60 if 



Mo = m, this being the number given by the most recent 



determinations. 



The process seems therefore to give very good quantitative 

 results, and is both easy and expeditious. The precipitated 

 molybdate separates easily from the filter and can be heated to 

 low redness without decomposition. 



Analogy would seem to offer a good method for tuugstic 

 acid and experimental analyses were made for this purpose, 

 but after repeated trials the process was finally abandoned, as 

 the precipitate came down so finely divided that it passea 

 through the filter. The precipitation seems, however, to be 

 complete, and I have hopes that with closer filter paper greater 

 success will be obtained. ♦ p 



Attempts were made to determine arsenic as arsenate oi 

 lead but without good quantitative results. On the other banc 



