818 EIGHTH PACIFIC SCIENCE CONGRESS 



Other 25 ml. aliquot, 1 ml. of 10% citric acid solution and 2 ml. of 

 A^-HCl were added, then 1 ml. of dithiol solution and heated on boiling 

 water for 10 minutes. And the molybdenum complex was extracted 

 with 10 ml. of butylacetate. The color intensity (Extinction E^) was 

 measured as above. 



The amounts of tungsten and molybdenum were calculated from 

 the following equations: 



ixgW = 58.8 X (E2 - El) 



/xg Mo = 83.0 X (El - 0.040) 

 It was found that through this procedure l-40y of molybdenum 

 and tungsten can be determined within dz0.5y 'of error, and this meas- 

 urements are only interfered by the presence of iron and copper. 



2. Concentration of Molybdenum and Tungsten in Sea Water 



For the purpose of separating and concentrating the molybdenum 

 and tungsten in sea water, we utilize the coprecipitation method as 

 follows: 



To 0.5-15 1. of artificial sea water (5), 1-3 ml. of HNO. and 200 mg. 

 ot ferric iron as ferric nitrate solution were added. Then 50-100 ml. 

 of IM hexamethylenetetramine solution was added, and allowed to 

 stand overnight to settle the precipitate. The precipitate Avas filtered, 

 dried and ashed in platinum crucible at low temperature lower than 

 500 °C. The residue was fused with small amounts of the fusing mix- 

 ture (NajCOa rt K2CO3 1:1). The fused mass was. taken up with 

 10-20 ml. of hot water, and filtered. The filtrate was just neutralized 

 with 4iV-H2S04 to litmus.* 



The results obtained are shown in Table I, nos. 1-9. 



Determination of tungsten in the presence of large amounts of 

 molybdenum: In the presence of large amounts of molybdenum 

 (>10 X W), tungsten was determined inaccurately by the above proce- 

 dure. In sea water, the amount of molybdenum may be about 30 times 

 larger than that of tungsten (4), so molybdenum was separated as sul- 

 fide from tungsten as follows: To the neutral solution *, 1 ml. of 50% 

 citric acid solution and 5 drops of iN-HoSO^ were added, and HoS bub- 

 bled vigorously for a few minutes. The sulfide was filtered through a 

 small filter, and washed with H2S water. The filtrate was evaporated 

 to a few ml., filtered again through the filter, if necessary, and washed 

 with hot water; and the solution was dried up in a platinum crucible. 

 The residue was ashed with a small amount of sodium carbonate and 

 fused. The mass was taken up in hot water and just neutralized with 

 H0SO4. The solution was diluted to 50.0 ml., and the amount of tungs- 

 ten and residual molybdenum was determined as above. 



* Residual molybdenum. 



