ATOMIC WEIGHTS 69 



The next series was made by Penny/ who worked after a somewhat 

 different method. He treated potassium chlorate with strong hydrochloric 

 acid in a weighed flask, evaporated to drjmess over a sand bath, and 

 then found the weight of the chloride thus obtained. His results are as 

 follows, in six trials : 



60.825 



60.822 



60.815 



60.820 



60.823 



60.830 



Mean, 60.8225, ± .0014 



In 1843 Pelouze ^ made three estimations by the ignition of the chlo- 

 rate, with these results : 



60.843 

 60.857 

 60.830 



Mean, 60.843, ± .0053 



Marignac, in 1842/ worked with several different recrystallizations of 

 the commercial chlorate. He ignited the salt, with the usual precau- 

 tions for collecting the material carried off mechanically, and also exam- 

 ined the gas which was evolved. He found that the oxygen from 50 

 grammes of chlorate contained chlorine enough to form .003 gramme of 

 silver chloride. Here are the percentages found by Marignac: 



In chlorate once crystallized 60.845 



In chlorate once crystallized 60.835 



In chlorate twice crystallized 60.833 



In chlorate twice crystallized 60.844 



In chlorate three times crystallized. . . . 60.839 



In chlorate four times crystallized 60.839 



Mean, 60.8392, ± .0013 



In the same paper Marignac describes a similar series of experiments 

 made upon potassium perchlorate. KCIO4. In three experiments it was 

 found that the salt was not quite free from chlorate, and in three more 

 it contained traces of iron. A single determination upon very pure 

 material gave 46.187 per cent, of oxygen and 53.813 of residue. 



iPhil. Trans., 1839, p. 20. 



^Compt. Rend., 15, 959. 



' Ann. Chem. Pharm., 44, IS. Oeuvres Completes, 1, 57. 



