FIRST TABLE OF ATOMIC WEIGHTS. 275 



atomic weight of sulphur as (12X 1*23) — 1 = 1376, which 

 number, standing half-way between 14*4, as given in the 

 first Table, and 13 as given in the second, points out the 

 origin of the first relative weight of the ultimate particle 

 of sulphur. So from sulphurous acid he would obtain a 

 similar number : taking the specific gravity as obtained by 

 him (part ii. p. 389) to be 2*3, and remembering that this 

 gas contains its own bulk of oxygen (p. 391), he obtained 

 (2*3— -1 *I2) x 12=14*16 for the atomic weight of sulphur. 

 As, however, we do not possess the exact numbers of his 

 specific-gravity determinations, and as we do not exactly 

 know what number he took at the time as representing the 

 relation between the densities of air and hydrogen (in 1803 

 he says that the relation of 1 : 0*077 is not correct, and 

 that -gV is nearer the truth), it is impossible to obtain the 

 exact numbers for sulphur as given in the first Table. 



In reviewing the experimental basis upon which Dalton 

 founded his conclusions, we cannot but be struck with the 

 clearness of perception of truth which enabled him to argue 

 correctly from inexact experiments. In the notable case, 

 indeed, in which Dalton announces the first instance of 

 combination in multiple proportion (Manch. Mem. vol. i. 

 ser. 2, p. 250), the whole conclusion is based upon an 

 erroneous experimental basis. If we repeat the experiment 

 as described by Dalton we do not obtain the results he 

 arrived at. Oxygen cannot, in fact, be made to combine 

 with nitric oxide in the proportion of one to two by merely 

 varying the shape of the containing vessel, although by 

 other means we can now effect these two acts of combina- 

 tion. We see, therefore, that Dalton's conclusions were 

 correct, although in this case it appears to have been a 

 mere chance that his experimental results rendered such a 

 conclusion possible. 



