S. J. Lloyd— Radium Content of Sea Water. 581 



and one-quarter liters of tins water were evaporated down to 

 750 cc whereby, of course, an abundant solid residue was 

 obtained. Five cc. of redistilled, concentrated hydrochloric 

 acid were added during the evaporation. Contrary to the 

 general opinion the presence of a precipitate does not necessa- 

 rily impair the accuracy of the determination,* especially when 

 several successive readings are made on the same sample. 



The measurements were made in the usual type of vacuum 

 electroscope with amber insulation. The transfer of the ema- 

 nation from the flask containing the evaporated sea water to 

 the electroscope was made essentially by McCoy's method,f 

 except that the emanation was collected over a warm saturated 

 solution of sodium chloride. For standardizing the electro- 

 scope, Joachimsthal pitchblende containing 46'2% of uranium 

 was employed. It was dissolved in nitric acid, diluted until 

 250 cc contained amounts of radium of the same order of mag- 

 nitude^: as the sample of sea water, and kept for thirty days 

 before using in order to ensure the presence of the maximum 

 amount of emanation. Following Rutherford it was assumed 

 that one gram of uranium is in equilibrium with 3'4 X 10~ 7 

 grams of radium. Heinemann and Marckwald§ have recently 

 obtained the value 3*328 for this constant, but the degree of 

 accuracy of the present measurements is not sufficient to make 

 it worth while to depart from the former value. 



Three successive determinations on the same sample gave 

 respectively 1*4, 1*75, and. 1*65 X 10~ 12 grams radium per liter. 

 As the first reading in such cases is usually low, the mean of 

 the last two was taken, and 1*70 assumed to be the correct 

 result. This figure is in comparative agreement with those of 

 Eve and of Satterly, and disagrees radically with that of Joly, 

 as is evident from the accompanying table : 



Grams Radium per liter of sea water. 



Joly 17- X 10- 12 



Eve (1907) 0-3 X 10" 12 



Eve (1909) .._ 0-9 X 10~ 12 



Satterly 1-0 X 10" 13 



Lloyd 1-7 X 10- 12 



It is difficult to account satisfactory for the extraordinary 

 discrepancy between Joly's results and all the others. A 

 repetition of his work on the waters which gave him the high- 

 est figures, notably those from the Irish coast (34- X 10~ 19 ) 



* J. Phys. Chem., xiv, 476, 1910. 



f J. Am. Chem. Soc. xxvii. 402, 1905. 



X Randall, Trans. Am. Electrochem. Soc, xxi, 496, 1912. 



§ Jahrbuch Radioakt. und Elelctronik, x, 299, 1913. 



