36 THE ATOMIC WEIGHTS. 



In the same paper Marignac describes a similar series of experiments 

 made upon potassium perchlorate, KC10 4 . 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. 



In 1845 two series of experiments were published by Gerhardt. * The 

 first, made in the usual way, gave these results : 



60.871 

 60.881 

 60.875 



Mean, 60.8757, .0020 



In the second series the oxygen was passed through a weighed tube 

 containing moist cotton, and another filled with pumice stone and sul- 

 phuric acid. Particles were thus collected which in the earlier series 

 escaped. From these experiments we get 



60.947 

 60.947 

 60.952 



Mean, 60.9487, .0011 



These last results were afterwards sharply criticised by Marignac,f 

 and their value seriously questioned. 



The next series, in order of time, is due to Maumene.J This chemist 

 supposed that particles of chlorate, mechanically carried away, might 

 continue to exist as chlorate, undecomposed ; and hence that all previous 

 series of experiments might give too high a value to the residual chloride. 

 In his determinations, therefore, the ignition tube, after expulsion of the 

 oxygen, was uniformly heated in all its parts. Here are his percentages 



of residue : 



60.788 

 60.790 

 60.793 

 60.791 

 60.785 

 60.795 

 60.795 



Mean, 60.791, .0009 



The question which most naturally arises in connection with these re- 

 sults is, whether portions of chloride may not have been volatilized, and 



css\ I /^a"f 



so lost 



* Compt. Rend., 21, 1280. 



} Supp. Bibl. Univ. de Geneve, Vol. I. 



I Ann. d. Chim. et d. Phys. (3), 18, 71. 1846. 



