214 Prof. J. Dewar on the Liquefaction of Oxygen 



merits was made by the action of water on zinc methyl, and 

 was therefore very pure, and that the observed critical pres- 

 sure was not 39 atmospheres, but 47*6. The following table 

 gives the values of the ratio of the absolute critical tempe- 

 rature to the critical pressure in the case of a number of 

 substances. The values for ammonia, sulphuretted hydrogen, 

 cyanogen, marsh-gas, and hydride of ethyl are new. 





T, 



Critical 

 temperature. 



P, 



Critical 

 pressure. 



T 

 P 



Chlorine Cl 3 



Hydrochloric acid HCl 



Oxygen 2 



Water H 2 



Nitrogen N 2 



Hydrogen sulphide H 2 S 



Ammonia H 3 N 



1410 



52-3 



-1130 



3700 



-146-0 



100-2 



1300 



220-0 



35-4 



155-4 



- 99-5 



37 



10-1 



35-0 



191-6 



2917 



2680 



282-0 



31-9 



277-7 



124-0 



83-9 



860 

 50-0 



195-5 

 35-0 

 92-0 



115-0 

 38-7 

 75-0 

 78-9 

 500 

 68-0 

 51-0 

 45-2 

 33-9 

 60-4 

 54-9 

 57-6 

 77-0 

 78-1 

 61-7 



50 

 3-7 

 3-2 

 3-3 

 3-6 

 40 

 3-5 



15-4 

 41 

 5-4 

 3-5 

 4-5 

 5-5 

 68 



13-7 

 9-3 

 9-9 

 9-6 

 40 

 70 

 6-4 



Diethylamine (C 2 H 5 ) 2 HN 



Nitrous oxide N 2 



Sulphurous acid S0 2 



Marsh-gas CH 4 



Acetylene C,H 



Ethylene C 2 H~ 



Ethyl hydride C 2 H 6 



Amylene C 5 H l0 



Benzol C 6 H R 



Chloroform CHC1 3 



Carbon chloride CC1 4 



Carbonic acid C0 2 



Bisulphide of carbon ... CS 2 

 Cyanogen C 2 N 2 



A glance at the last column of the table shows that a large 

 number of substances have at their respective critical tem- 

 peratures simple volume relations. Thus hydrochloric acid, 

 water, ammonia, and marsh-gas, the four chemical substances 

 from which the great majority of chemical compounds may 

 be derived by processes of substitution, have nearly the 

 same volume ; while the more complex derivatives show an 

 increased volume which bears a simple ratio to that of the 

 typical body. As the critical pressures are not known with 

 any great accuracy at present, it would be useless to discuss 

 the results with any severity. All that can be inferred is 

 that the subject is worthy of further investigation and pro- 

 mises important generalization. Sarrau (Compt. Rend. 1882) 

 deduced the critical temperatures and pressures of hydrogen, 

 oxygen, and nitrogen by the application of Clausius' formula 

 to the experiments of Amagat; and it is interesting to compare 

 his results with the experimental values. 



