OF ARTS AND SCIENCES. 209 



The first column of this table indicates the ori<;inal number of the 

 experiment. The data of Experiments 17 and 38 are given for 

 the first time. The second column shows the source of the acid. The 

 third column gives the weights of sodic carbonate taken ; while in the 

 fourth are recorded the indicators used in determining: these weishts, 

 the abbreviations standing for methyl orange, phenol phthalein, or the 

 average of the two. The last two columns contain respectively the 

 weight in grams and the molecular weight of the sodic sulphate. 

 Since half of the results were obtained with methyl orange, it is un- 

 necessary to correct the result for the trace of impurity in the sodic 

 carbonate. 



Subtracting from the averages the quantity 'Na.fii = 110.106 we 

 obtain two values for the atomic weight of sulphur : — 



From the first average, S = 32.063 



" second average, S = 32.075 



Usually accepted value, S = 32,06 



A large alteration in the assumed atomic weight of sodium would of 

 course make very little difference in the result, while an alteration 

 of xxiVo ^^ '^^^ value in the atomic weight of carbon changes the 

 atomic weight of sulphur by only about the twentieth of one per cent. 

 Although it is certain that the results are hardly capable of deciding 

 the present uncertainty in the atomic weight of sulphur, the outcome 

 of the comparison is nevertheless an interesting check upon the work 

 previously described. 



The check just mentioned proves that the sodic carbonate contained 

 the normal amount of carbon dioxide, but does not prove the absence 

 of a very small amount of neutral impurity from the salt. Such 

 impurity would have but a slight effect upon the ratio of the weights 

 of the two compounds. It is true that this effect would be to di- 

 minish instead of to increase the observed atomic weight of sulphur; 

 but it was thought advantageous to attempt the comparison of the 

 sodic carbonate with some salt having a very different equivalent 

 weight, in order to obtain more light upon this point. Accordingly 

 the material to be investigated was converted with suitable precautions 

 into sodic bromide. In Experiment 39, 1.2198 grams (in vacuum) 

 of sodic carbonate yielded 2.3685 grams (in vacuum) of the bromide ; 

 or 2 NaBr : NaoCOg = 206.022 : 106.103. Upon its face the result 

 was very satisfactory, but the great hygroscopic power of sodic bromide 

 and various other complications afforded a wide possibility of error; 

 hence the experiment was not repeated. To be of value, any such 



