236 PROCEEDINGS OF THE AMERICAN ACADEMY. 



a nephelometer, the usual precautions being taken to secure uniformity 

 of precipitation.^ 



When the ratio of the neodjonium chloride to metallic silver was to 

 be determined a quantity of silver equivalent to the chloride within a 

 very few tenths of a milligram was weighed out and dissolved in nitric 

 acid in a flask fitted with a column of bulbs to prevent loss of material 

 by spattering. The quantity of silver was adjusted exactly by means 

 of a hundredth normal solution of silver. After the silver solution had 

 been freed from oxides of nitrogen it was diluted to a volume of one 

 liter and was quantitatively added to the chloride solution. The pre- 

 cipitate was caused to settle completely by occasional shaking and 

 standing for several days. Then portions of the mother liquor were 

 tested for excess of silver or chloride by the addition of hundredth 

 normal chloride or silver nitrate solutions, and comparison of the opal- 

 escence produced in a nephelometer. Deficiencies in either chloride or 

 silver were made up by means of the dilute standard solutions of these 

 substances until finally exactly equivalent amounts of chloride and 

 silver were present in the solution. 



In all except the first two titrations the solubility of the silver chlo- 

 ride in the mother liquor was very much decreased by cooling the solu- 

 tion with ice water, a method of increasing the accuracy of nephelometric 

 observation which has been devised recently by Richards and Willard 

 and used successfully in their revision of the atomic weight of lithium.^ 



As soon as equilibrium had been reached in a titration, an excess of 

 one tenth of a gram of silver nitrate was added and the silver chloride 

 was determined gravimetrically as described above. Corrections were 

 of course applied for any chloride added in the titration. 



The Determination of the Moisture Retained by the 

 Neodymium Chloride. 



Although in several cases where hydrated salts have been dried by 

 efflorescence it has been shown that the moisture retained by the salt 

 is negligible in quantity,*^ in the present instance careful experiments 

 were instituted to test this point thoroughly. The direct determina- 

 tion of the water by absorption with phosphorus pentoxide, after fusion 

 of the salt, was complicated in the case of neodymium chloride, since, 



^ Richards and Wells, Amer. Chem. Jour., 31, 235 (190-4); 35, 510 (1906). 

 Richards and Stahler, Pub. Car. Inst., No. 69, 20 (1907); Jour. Amcr. Chcm. 

 Soc, 29, G35. 



2 Pub. Car. Inst,., No. 125, 30 (1910); Jour. Amer. Chom. Soc, 32, 32. 



3 Baxter and Coffin, Jour. Amer. Chem. Soc, 28, 15S7 (190G); Baxter and 

 Tilley, Ibid., 31, 212 (1901). 



