196 SCIENCE PROGRESS 



combination. According to him what we term hydroxyl or 

 single-linked oxygen had the value 7*8 whereas carboxyl or 

 doubly-linked oxygen was i2'2. These values are not very 

 dissimilar to those now current. The interesting point is that 

 Kopp was the first to detect the effect of what we now term 

 constitution on molecular volume, and thus the first to 

 familiarise us with the conception of its general influence. 

 More extended inquiry has shown that in reality oxygen 

 possesses a number of values depending upon its environment, 

 position, function, etc., and limiting values are now known 

 with approximate accuracy for the various types of com- 

 bination, e.g. hydroxylic, ethereal, ketonic, etc., both in 

 aromatic and aliphatic compounds. 



Space will not allow us to pursue this particular matter at 

 length, but we may point out as a matter of general interest 

 its bearing on the question of the molecular constitution of 

 liquid water. Water is known to be what is called an " asso- 

 ciated " substance. A number of physical facts combine to 

 show that the formula H 2 does not represent its nature as a 

 whole under any conditions, so far as is known, so long as it 

 remains liquid. Ordinarily water is made up of molecules 

 which are polymers of H 2 0, in amount depending upon tem- 

 perature. Its formula therefore is (HsO)* where x is greater 

 than unity. 



The determination of its molecular volume at its boiling- 

 point would seem to show that strictly speaking it is not a 

 hydroxyl compound at all, but is, in reality, the first term of 

 the Symmetrical Ether Series, just as hydrogen is " the 

 vanishing point " of the paraffins. 



Combined sulphur, like oxygen, has at least two molecular 

 volumes depending upon circumstances similar to those indi- 

 cated in the case of oxygen : one of these values is identical 

 with the molecular volume at its boiling-point in the un- 

 combined state. The molecule of liquid sulphur is known to 

 be very complex — probably S10 and Sg ; that of gaseous sulphur 

 is S 6 or S 2 , depending upon temperature. A knowledge of its 

 molecular volume throws light upon the structure of the 

 sulphur molecule and serves to explain the phenomena of 

 colour and ease of decomposition. 



Information as to the molecular volumes of the halogen 

 derivatives of sulphur, and of its oxides, and of a number 



