M. Stas on the Determination of Atomic Weights. 3 97 



The observations varied between 174*079 and 174097. 

 Complete analysis of iodate of silver. — A weighed quantity of 

 the salt is decomposed by ignition, and the iodide of silver 

 weighed, as well as the oxygen which escapes. The decompo- 

 sition was effected in a current of nitrogen, in an apparatus in 

 which iodine that had become free, or particles mechanically 

 carried away, could be held back. The iodate of silver was con- 

 tained in a glass bulb, provided on each side with long tubulures, 

 on which metallic tubules with cocks were placed. In one of 

 these tubulures, which was somewhat narrower, there was first of 

 all a stopper of silver wire, then some asbestos treated with aqua 

 regia and ignited, thereupon a layer (15 to 18 centimetres in 

 length) of finely divided silver, prepared by precipitating in the 

 cold solution of silver with sulphite of ammonium. Then there 

 was again asbestos, fine silver wire, and finally a spring of silver 

 wire which held all the parts together. 



For the absorption of the oxygen a tube was used 75 to 80 

 centims. in length, provided with metallic cocks, which first 

 of all contained a stopper of metallic wire, then a layer 10 to 12 

 centims. in length of copper turnings, 10 centims. of copper 

 reduced from oxide of copper at a high temperature by carbonic 

 oxide, 20 centims. of copper reduced at a low temperature, and 

 then slightly oxidized copper turnings, to burn any hydrogen that 

 might have been formed. It was then closed, first, with a fine 

 copper wire, then asbestos, and lastly a spring of copper wire, 

 which prevents the removal of the mixture by a current of air. 

 The oxide of copper used was prepared by the ignition of nitrate 

 of copper, and was boiled with caustic potash until it was free 

 from sulphur. 



The iodate of silver retains persistently some water ; and hence 

 the tube containing the copper was connected with three U-tubes, 

 40 centims. in length and 2\ centims. internal diameter. The 

 tubes were filled with pieces of pumice, which were twice mois- 

 tened with sulphuric acid, then ignited, filled in while still hot, 

 and while at a temperature of 300° so much sulphuric acid added 

 that the latter was at a height of 1^ centim. in the bend of the 

 tube. After filling, the tubes were drawn out and joined by 

 caoutchouc tubes, which were then bound round with silver foil. 



A fourth, smaller U-tube served as a control, and, lastly, a fifth 

 as a protection of the four against the atmosphere. 



The nitrogen, prepared by passing air over copper, was con- 

 tained in a large gas-holder, to the water of which a solution of 

 hydrated protoxide of tin in potash was added, to absorb O and 

 CO 2 . The nitrogen is first passed through a tube containing 

 sulphuric acid, then through two CaCl tubes, then over a layer 

 of ignited copper 90 centims. in length (reduced from oxide of 



