Oxygen by Sulphur on Boiling-points of Compounds. 461 

 Such, for example, are the following : — 



H.,S .. 



CH,SH 



■61-8 

 21 



(OH 3 ) 2 S 41 



64 



H 2 S -618 



C 2 H 5 SH... 36 

 (C 2 H S ) 2 S... 92 

 Pr a 8'(i)...130 



H,S -618 



C 6 "H 5 SH ... 172 

 6 H 5 SC 2 H 5 204 

 (C 6 H 5 ) 2 S ... 292 



Taking in the same way the corresponding oxygen com- 

 pounds, we find that by replacing OH by OX, where X 

 stands for any hydrocarbon radical, unless very complex, we 

 lower the boiling-point of the compound considerably, whereas 

 when the exchange is simply between different hydrocarbon 

 radicals the change is in the normal direction. 



100 



B, 



H o .... 



CH 3 OH 67 



■23 

 11 



(CH 3 ) 2 ... ■ 

 CH 3 2 H 5 0... 



H\,0 100 



C o H 5 0H 78-4 



(d.;fi 5 ) 2 o ... 35 



(Pr 2 )0 (.)... 82 



H 2 100 



(0 6 H 5 OH ... 180 

 6 H 5 00 2 H 3 ... 172 

 (0 6 H 3 ) 2 246* 



From these data it is evident that the fact that water, 

 which has a lower molecular weight than even any of the 

 "permanent" gases (except hydrogen) will remain liquid up 

 to a very high temperature, is only one particular and well- 

 marked case of the general effect of the hydroxy 1 group. 



It has been objected by Ostwald and others that the com- 

 parison of boiling-points is unsatisfactory, inasmuch as in 

 some cases it is possible that the vapour-pressure curves of 

 different substances may cross one another at some point; and 

 in that case, if some other than atmospheric pressure were 

 taken as the standard, the relative position of the boiling- 

 points would be reversed. 



It is difficult to plot the vapour-pressure curves for H 2 

 and H 2 S on the same scale, since the pressure of H 2 S varies 

 by many atmospheres ; while that of H 2 varies through the 

 same range only by a few inches, so that it has to be repre- 

 sented on the H 2 S scale by a line following the zero. The 

 H 2 S curve is, however, perfectly normal, and shows no ten- 

 dency whatever to approach the zero at any point short of 

 infinity. Hence the objection about the crossing of the 

 curves falls to the ground in this case. The same may be 

 shown by comparing the curves for C0 2 and CS 2 ; only in 

 this case, of course^ the sulphur compound follows the zero 

 line, while the other is highly inclined. 



With regard to the melting-points of oxygen and sulphur 

 compounds the same general rule holds ; but exceptions are 

 not rare, particularly in the cases of more complicated com- 

 pounds, and naturally it is among these that the larger number 



* la this case the destruction of OH is not sufficient to balance the 

 effect of introducing the second carbon ring. 



Phil. Mag. 8. 5. Vol. 35. No. 216. May 1893. 2 1 



