IO8 ABSOLUTE ATOMIC WEIGHT. 



The dry way, almost exclusively used by Berzelius, is the 

 only way to employ if the element concerned permits it. 



The final result is that the atomic weight, within the 

 precision of the determinations, is 40 exactly. The experi- 

 mental determinations show that the actual atomic weight 

 does not differ as much as o.oi from the standard. 



IX. THE ATOMIC WEIGHT OF MAGNESIUM. SCHEERER. 



Marchand and Scheerer, in 1850, selected the purest 

 natural magnesites for the determination of the atomic 

 weight of magnesium by the direct dry way process, used so 

 effectively for calcium. 



They selected three very fine varieties of this mineral. 

 A yellow, transparent magnesite from Snarum; a white, 

 opaque variety from the same locality and a very pure, but 

 opaque, white variety from Frankenstein. 



Chemical examinations, made with extreme care, by 

 Scheerer, revealed the presence of o.oo 225 of lime (Ca O) 

 in the Frankenstein magnesite, and o.oo 430 of lime 

 together with o.oo 776 of ferrous oxide in a unit of weight 

 of the Snarum magnesite. 



Scheerer uses the results from both localities; but we 

 deem such process irrational, because the iron is likely to 

 change its degree of oxidation, and even if it does not under 

 the circumstances, the purer substance must always be 

 preferred. 



We, therefore, exclude all data obtained from the Snarum 

 magnesite, also the first two series of determinations made 

 with Frankenstein's magnesite, and use exclusively the third 

 series made upon the purest material of this fine variety. 



Now, the 225 of Ca O found require 177 CO2 and con- 

 stitute 402 of Ca Oa C in the magnesite used, leaving of 

 actual Mg Oa C only 99 598 all figures in fifth place. 



The mean residue of the four determinations of this third 

 series amounted to 47 642 ; since 225 was Ca O, the true 

 Mg O amounted to 47 417 only. 



But this in the 99 598 of pure magnesium carbonate 

 amounts to 0.47 608 per unit. 



