6 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



Nevertheless, he was by no means infallible, as his long oversight of 

 the solubility of argentic chloride, his difficulty in obtaining colorless 

 amnionic bromide, the uncertainty concerning the oxygen in his silver, 

 and the recent proof of an important error in his work on iodine,* 

 all testify. Moreover, Stas's work is not to be considered as accurate 

 in proportion to the scale of his experiments, as many have been 

 inclined to suppose. Mere increase in quantity of material can 

 avail nothing if the same physico-chemical error or the same chemi- 

 cal impurity contaminates the whole. Indeed, it is doubtful if beyond 

 a moderate scale of operations increase of quantity decreases even 

 the probability of accidental error. For example, the extreme varia- 

 tions in his work on the synthesis of argentic chloride, in which 

 on the average nearly 200 grams of the compound were weighed 

 in each analysis, amounted to 0.006 per cent, or 12 milligrams of 

 material.! An accuracy of 0.6 milligram with 10 grams of sub- 

 stance, very easy to attain as far as the collection and weighing of 

 the material is concerned, would have brought him as good agreement. 

 But large quantities have no advantage to offer besides the increased 

 accuracy in weighing and the diminished percentage effect of a given 

 accidental loss of material in transference. For this reason the use 

 of extremely large quantities must rather be considered as evidence 

 of a lack of sound judgment than an index of unusual accuracy. Stas 

 himself acknowledged this by using only about 10 grams of material 

 in each of his last experiments.! 



Regretfully one must admit that a critical study of the work of 

 Stas upon sodium in particular reveals several possibilities of error, as 

 well as at least one inconsistency. He analyzed both the chloride and 

 the bromide ; of these salts the former received the greater attention, 

 and will be discussed here in greater detail. 



In reviewing his results upon sodic chloride there are two series 

 to be considered, separated by an interval of time of over twenty years. 

 Although at first sight these two series seem to have yielded almost 

 identical results, asi a matter of fact they are essentially inconsistent 

 with one another. Both results were obtained by the method of Gay- 

 L-ussac, titrating weighed amounts of silver in solution with salt ; but 

 at the earlier time the latter was added until all precipitation ceased, 

 while at the later time equivalence was assumed when the supernatant 

 liquid gave equal opalescence with excess of either chloride or silver. 



*The work of Ladenburg and Scott has been confirmed by Dr. G. P. Baxter, 

 of Harvard University, whose recent analyses show that the atomic weight of 

 iodine can hardly be lower than 126.97. Proc. Acad., 40, 419 (1904). 



tj. S. Stas, Oeuvres completes 1, 341 (Brussels, 1894). JOeuvres, 3, 503. 



