218 THE ATOMIC WEIGHTS. 



Cooke has since shown, is a possible source of error, for under such 

 circumstances the crystalline argento-antimoiiious tartrate may also be 

 thrown down and contaminate the chloride of silver. But be that as it 

 may, Dumas' weighings, reduced to a common standard, give as propor- 

 tional to 100 parts of silver, the quantities of SbCl 3 which are stated in 

 the third of the subjoined columns : 



i.876grm. SbCl 3 = 2.66o grm. Ag. 70.526 



4.336 " 6.148 " 70.527 



5.065 " 7.175 " 70.592 



3-475 4-93 " 70.487 



3.767 5.350 70.411 



5.910 " 8.393 " 70.416 



4.828 " 6.836 " 70.626 



Mean, 70.512, .021 



Hence, if Ag = 108, and Cl = 35,5, Sb = 122. 



In 1861 Kessler's second paper * relative to the atomic weight of an- 

 timony appeared. Kessler's methods were somewhat complicated, and 

 for full details the original memoirs must be consulted. A standard 

 solution of potassium dichromate was prepared, containing 6.1466 

 grammes to the litre. With this, solutions containing known quantities 

 of antimony or of antimony compounds were titrated, the end reaction 

 being adjusted with a standard solution of ferrous chloride. In some 

 cases the titration was preceded by the addition of a definite weight of 

 potassium chlorate, insufficient for complete oxidation ; the dichromate 

 then served to finish the reaction. The object in view was to determine 

 the amount of oxidizing agent, and therefore of oxygen, necessary for 

 the conversion of known quantities of antimonious into antimonic com- 

 pounds. 



In the later paper Kessler refers to his earlier work, and shows that 

 the values then found for antimony were all too high, except in the case 

 of the series made with tartar emetic. That series he merely states, and 

 subsequently ignores, evidently believing it to be unworthy of further 

 consideration. For the remaining series he points out the sources of 

 error. These need not be rediscussed here, as the discussion would have 

 no value for present purposes ; suffice it to say that in the series repre- 

 senting the oxidation of Sb 2 s with dichromate and chlorate, the ma- 

 terial used was found to be impure. Upon estimating the impurity and 

 correcting for it, the earlier value of Sb = 123.80 becomes Sb = 122.36, 

 according to Kessler's calculations. 



In the paper now under consideration four series of results are given. 

 The first represents experiments made upon a pure antimony trioxide 

 which had been sublimed, and which consisted of shining colorless 

 needles. This was dissolved, together with some potassium chlorate, in 



*Poggend. Annalen, 113, 145. 1861. 



