of Hydrocarbons and their Mixtures. 361 



That which prevails throughout the rectilinear marsh-gas- 

 ethylene mixtures is #='184:0. The illuminating value of 

 unit precipitated carbon in the mixtures is 200 # 6, larger than 

 that of ethylene in the table (180). It is obvious that a 

 mistake was made in the table in taking the " indirect n C.P. 

 of ethylene (65) as fundamental, instead of the observed 

 number 68*5. But it is only now that I am convinced as to 

 the right course. 



Taking ethylene, #=*5, ?/=68'5, 

 ethane, ^'=3? 3/ = 35, 

 the point in which a line through both meets the x axis is 

 # = •1592. This would be the correct " disilluminate hydro- 

 carbon centre," if the method of the last paper were followed. 

 It represents the solvent capacity of combined hydrogen for 

 carbon density 2. 



I assume that the solvent capacity *1840, which prevails in 

 the rectilinear portion of the marsh-gas-ethylene mixtures, 

 belongs to marsh-gas, or carbon density 1. The explanation 

 of this is a little difficult ; but I take it in this way : — The 

 difference of solvent capacity between the hydrogen of marsh- 

 gas and ethylene is *1840 — * 1592 = '0248. There is more 

 than this amount of carbon in the form of marsh-gas in all 

 the mixtures. So long as there is enough marsh-gas to fill 

 up the chinks, so to speak, left by the carbon of the ethylene, 

 the total absorbed carbon (or capacity) remains at the larger 

 value. When there is not enough marsh-gas to afford carbon 

 equal to the difference, the capacity would be less. And 

 when the ethylene is pure, the capacity has the lower value, 

 whence follows the additional precipitation, which gives rise 

 to the curvature in question. 



As to the illuminating value, or C.P. equivalent of precipi- 

 tated carbon, the number given by ethylene and ethane is, 



68-5-35 



*- 



i 



= 201, 



and that given by the equation to the mixtures is 200*6. 



The marsh-gas-ethylene mixtures will not bear any explana- 

 tion which attributes different values to the carbon from the 

 two sources ; and the value of the precipitated carbon is that 

 of the higher component (ethylene). The explanation of this 

 is not clear ; but it seems as if it depended on the way in 

 which the first nuclei of precipitation bring down the rest of 

 the carbon. This cannot apply to marsh-gas itself ; and it 

 seems that the " theoretical " position of the marsh-gas point 

 involves the supposition that the carbon has the same value as 



