40 



RESEARCHES UPON ATOMIC WEIGHTS. 



was due to adsorption of manganese compounds by the filter-paper. In order 

 to test this point a solution of manganous bromide, containing about 5 gm. 

 in 200 c.c, after one filtration was again filtered through a second filter about 

 3 cm. in diameter. Filters of this size were used in filtering the manganous 

 bromide solution in the analyses. This filter was then washed with water as thor- 

 oughly as in an analysis, and was ignited. The weight of manganic oxide ob- 

 tained was 0.00008 gm. Two repetitionsof the experiment jdelded 0.00008 and 

 0.000 10 gm. respectively. If, as is probable, the manganese is adsorbed, not as 

 bromide, but as some basic compound, possibly as manganic hydroxide, the bro- 

 mine would have remained partially, if not wholly, in the solution. In that case 

 a suitable correction could be appKed by subtracting from the weight of the 

 residue the average of the quantities of manganese adsorbed in the above exper- 

 iments. An attempt to prevent the difl&culty by adding dilute sulphuric acid 

 to the solution of manganous bromide did not diminish the extent of the adsorp- 

 tion. Hence a negative correction of 0.00009 gm. is applied to the residue in all 

 cases. 



It has already been shown that chlorides and bromides which have been 

 fused and allowed to solidify in an acid atmosphere occlude none of the gas, for 

 they give neutral solutions.^ 



THE DENSITY OF MANGANOUS BROMIDE. 



In order to find accurately the vacuum correction for manganous bromide, 

 it was necessary to determine the density of this salt. The experiments were 

 carried out exactly as described in our determinations of the specific gravities 

 of cadmium halides,^ with the following results: 



Density of MnBr2. 

 Density of To'uol 25°/ 4° = 0.86156. 



The average density of several of the brass weights was found by displace- 

 ment of water to be 8.3. 



1 Richards: Proc. Amer. Acad., 29, 59 (1893); Zeit. anorg. Chem., 6, 93 (1894); Jour. 

 Amer. Chem. Soc, 24, 376 (1902); Zeit. anorg. Chem., 31, 273; Richards and Baxter: Proc. 

 Amer. Acad., 34, 367 (1899); Zeit. anorg. Chem., 21, 269; Baxter and Hines: Jour. Amer. 

 Chem. Soc, 27, 227 (1905); Zeit. anorg. Chem., 44, 163. 



» Amer. Chem. Jour., 31, 220 (1904). 



