64 ABSOLUTE ATOMIC WEIGHT. 



atomic weight of nitrogen, the corner stone of the system 

 of Stas and his school. 



Then will follow the complete record of all experimental 

 determinations made during the century, in alphabetic order 

 of the symbols of the elements. 



Atomic Weight Calculation Made Easy. 



We have not yet shown how the exact atomic weight cor- 

 responding to any given analytical ratio can instantly be 

 obtained by a simple mental calculation. This is due to the 

 fact that we here really are making use of a very refined 

 method of mathematical analysis, although we wish the 

 chemical reader not to get aware of it for he might shy. 



We may suppose that every body understands that all 

 quantitative relations can be graphically represented by a 

 curve drawn to scale, and that at any point of such a curve 

 the element of the curve may be considered a straight line 

 (the tangent) for a distance sufficiently short. 



But then the changes of the variables, the co-ordinates, 

 will be directly proportional within that limit. 



Hence, for small changes the analytical excess tvill be 

 directly proportional to the corresponding change in the atomic 

 IK} eight. 



Now nothing is easier than to determine and express this 

 change in a uniform manner. For we need only calculate 

 the atomic ratio say for an increase of o.i of the standard 

 atomic weight, to find the change in atomic weight corres- 

 ponding to any analytical excess. 



In the above instance, we found the standard atomic ratio. 

 Hg : Hg O = 200 : 216 = 0.92 593. 



Suppose now that the trite atomic weight of mercury 

 were 200.1, then the true atomic ratio would be 

 Hg : Hg O = 200.1 : 216.1 =0.92 596. 



The supposed true atomic ratio in this case would simply 

 be tl 3 high " as compared to the standard atomic ratio, 

 using our simple method of expression for the excess being 

 3 units in the fifth place. 



