262 THE ATOMIC WEIGHTS. 



nitre. Such silver Dumas heated to redness in a Sprengel 

 vacuum, and found that it gave up weighable quantities of 

 oxygen, which had been absorbed by the metal when in the 

 melted state. In one experiment a kilogramme of silver 

 gave 82 milligrammes of occluded gas, and in three other 

 cases 226, 140, and 249 milligrammes respectively were found. 

 In other words, the silver which had been considered pure 

 by Stas and others, was really not pure, and a correction 

 became necessary in nearly all series of atomic weight de- 

 terminations. 



The amount of this correction, which I think may here- 

 after be appropriately designated as " Dumas' correction," 

 will naturally vary in different cases, and in no particular 

 case can we tell, without actual examination of the silver 

 employed, exactly how great it should be. ' We may, how- 

 ever, assume that all the metallic silver heretofore used in 

 establishing atomic weight ratios was subject to it; and, 

 reckoning from the largest error indicated in the experi- 

 ments of Dumas, namely, 249 milligrammes of oxygen in 

 the kilogramme of metal, we may ascertain its tendency 

 with reference to Front's law. 



In the chapter upon the atomic weights of silver, chlorine, 

 bromine, iodine, potassium, sodium, and sulphur, twenty 

 ratios are given, of which nine are subject to Dumas' cor- 

 rection. Applying it as suggested above, we get the follow- 

 ing results. The values previously found and given in the 

 chapter just quoted, we may designate as uncorrected. For 

 convenience in future reference I assume that = 16 : 



Uncorrected. Corrected. Difference. 



Silver 107.923 107.896 — .027 



Chlorine 35-451 35-47S +-027 



Bromine . 79-951 79-97^ + •^'^1 



Iodine 126.848 126.875 -f -027 



Potassium 39- 109 39-0S3 — .026 



Sodium . 23.051 23.024 — .027 



Sulphur 32.058 32.058 



The result of the correction, it will l>e seen, is generally 

 favorable to Front's hypothesis. Of the seven elements 



