276 M. R. Schneider on Equivalents, and 



of all these numbers ; that is, foi- the one whose accuracy should 

 have been ascertainable with the greatest ease and certainty. 

 Instead of the equivalent of magnesium, those of tellurium and 

 osmium have now been brought into this series, the one with 

 the equivalent 64-5, the other with that of 99-5. The experi- 

 ments upon which these numbers are based have not yet been 

 communicated. The number 64'"5 for tellurium is not in har- 

 mony with that of Berzelius, 64"14, nor with that of V. Hauer*, 

 64'0. With regard to the equivalents of manganese, of nickel, 

 and of cobalt, I think I have sufficient reason to doubt the ac- 

 curacy of the law, in consequence of my own determinations ; 

 so that there only remain those which have been formerly and 

 latterly determined several times with care by Marignac, and 

 which are certainly very nearly exact multiples of 0*5, namely, 

 chlorine 35'5, barium 685, and lead 103"5. 



Convinced as I am that these numbers must be retained as 

 long as their incorrectness remains unproved by other experi- 

 ments, I still hold that at present no other meaning can be 

 given to them, than that they form isolated exceptions to the 

 general law ; the attempt to collect these few exceptions to a 

 special law must, in my opinion, be considered as premature. 



It is remarkable that, in the majority of the new equivalent 

 determinations of Dumas, the composition of the chlorides has 

 been taken as a starting-point. I have already expressed my 

 doubt concerning the employment of this method so generally. 

 I need not repeat it here. In the mean time some examples 

 may be cited, sufficient to show that such a doubt is not without 

 some foundation. 



The equivalent of magnesium has been universally taken as 

 12, since the excellent determination of it by Marchand and 

 Scheererf* M. Dumas J all at once gives it the number 13'5, 

 and introduces it into the series of numbers which, according 

 to him, follow the laio of being multiples of half an equivalent 

 of hydrogen. In order to do this, he must have been fully con- 

 vinced of the reliability of the method he pursued, and of the 

 purity of the substance employed (chloride of magnesium); other- 

 wise he would not have jmblished a number which is so opposed 

 to the received number — he would not have employed it to 

 prove a law of relation. When, however, in the latest publica- 

 tion of M. Dumas §, we find it stated that all the determinations 

 of the equivalent of magnesium from which the number 12'5 was 

 derived are subject to an error introduced by impurity in the 



* Sitzungsber. der Wien. Acad. vol. xxv. p. 139. 



t Journal fur Pract, Chem. vol. 1. p. 385. 



J Comptes Rendus,vo\. xlvi. p. f)51. 



§ Ann. de Chim. et de Phys. (3) vol. Iv. p. 190. 



