of Hydrocarbons and their Mixtures. 365 



a rule on the part of the curve in question, and judging where 

 it would meet the y axis. For the 16-candle region I take, 



for nitrogen . . y = — 1 0, 

 for carbonic acid . y= —100, 



though I have not used this last practically. 



The constant for hydrogen is otherwise determined later. 

 I previously estimated the hydrogen point as y=0. It 

 appears to have a small positive value. 



Illuminating Values. 



The following is a table similar to that in my last paper, 

 embodying the amended illuminating values. The centres 

 represent the solvent capacities of the hydrogen, or the 

 absorbed carbon, since the hydrogen is always saturated in 

 hydrocarbons. 



The values are formed into a scheme proceeding by the 

 law of the former table, which commends itself. It will be 

 seen later that owing to the absorption in the disilluminated- 

 gas mixtures we can obtain no direct information from the 

 available experiments as to the C.P. of benzene, except that 

 it is greater than 240. The value derived from this table 

 rests on the assumed law, viz. that the differences of I.Y. 

 form a geometrical series, having the first I.V. for its first 

 term. 



Illuminating Values and Solvent Capacities in Hydrocarbons. 



H.S.C. Hydrogen solvent capacity = absorbed carbon. 

 I.V. Illuminating value of precipitated carbon. 

 CD. Carbon density. 



78 



CD. H.S.C. I.V. Differences. 



1 -1840* 123 



2 -1592* 201 4 



3 250* ** 



4 281 I] 



5 300 \l 



6 312 lz 



Ratio of series, 123 and differences, -63. 



* Data:— 



H.S.C. '1840 from the marsh-gas-ethylene equation. 

 H.S.C. -1592 and I.V. 201 from :— 



Ethylene, .r=-5, 2/=68*5 : Ethane ff=|, y=35. 

 54 

 LV ' 250 = -3750- -1592 ( Pro P ane )' 



