34 THE ATOMIC WEIGHTS. 



SILVER, POTASSIUM, SODIUM, CHLORINE, BROMINE, AND 



IODINE. 



The atomic weights of these six elements depend upon each other to 

 so great an extent that they can hardly be considered independently. 

 Indeed, chlorine, potassium, and silver have always been mutually de- 

 termined. From the ratio between silver and chlorine, the ratio between 

 silver and potassium chloride, and the composition of potassium chlo- 

 rate, these three atomic weights were first accurately fixed. Similar 

 ratios, more recently worked out by Stas and others, have rendered it 

 desirable to include bromine, iodine, and sodium in the same general 

 discussion. 



Several methods of determination will be left altogether out of account. 

 For example, in 1842 Marignac* sought to fix the atomic weight of 

 chlorine by estimating the quantity of water formed when hydrochloric 

 acid gas is passed over heated oxide of copper. His results were wholly 

 inaccurate, and need no further mention here. A little later Laurent f 

 redetermined the same constant from the analysis of a chlorinated de- 

 rivative of naphthalene. This method did not admit of extreme accu- 

 racy, and it presupposed a knowledge, of the atomic weight of carbon ; 

 hence it may be properly disregarded. Maumene's J analyses of the 

 oxalate and acetate of silver gave good results for the atomic weight of 

 that metal; but they also depend for their value upon our knowledge of 

 carbon, and will, therefore, be discussed farther on with reference to that 

 element. Hardin's work also, relating to the nitrate, acetate, and 

 benzoate of silver, will be found in the chapters upon nitrogen and 

 carbon. 



Let us now consider the ratios upon which we must rely for ascertain- 

 ing the atomic weights of the six elements in question. After we have 

 properly arranged our data we may then discuss their meaning. First 

 in order we may conveniently take up the percentage of potassium chlo- 

 ride obtainable from the chlorate. 



The first reliable series of experiments to determine this percentage 

 was made by Berzelius. || All the earlier estimations were vitiated by 

 the fact that when potassium chlorate is ignited under ordinary circum- 

 stances a little solid material is mechanically carried away with the 

 oxygen gas. Minute portions of the substance may even be actually 

 volatilized. These sources of loss were avoided by Berzelius, who de- 

 vised means for collecting and weighing this trace of potassium chloride. 



*Compt. Rend., 14, 570. Also, Journ. f. Prakt. Chetn., 26, 304. 

 tConipt. Rend., 14, 456. Journ. f. Prakt. Chem., 26, 307. 

 t Ann. d. Chim et d. Phys. (3), 18, 41. 1846. 

 g Journ. Arner. Chem. Soc. 18, 990. 1896. 

 j| Poggend. Annalen, 8, i. 1826. 



