( 525 ) 
less than 198 atm. so that it will differ much from the critical 
pressures of most of the other substances. And in the second place the 
value of v, is here so extraordinarily variable with the temperature. 
Water is in this respect exceptional in Nature, and gives therefore 
rise to very peculiar phenomena, which are not found with other 
substances, or not in that degree. Alcohol e.g. is also an anomalous 
substance, but neither is the variability of the molecular volume 
there particularly great, nor the critical pressure particularly high. 
We know, that the variation of the molecular volume finds its 
cause in the decomposition of the double molecules with the temperature. 
gradually grows smaller and smaller, the quantity 
(eVa Va), 
which principally determines the value of 7, will become greater 
and greater. And the initial value of that quantity is in the case 
of water as one of the components already higher than for mixtures 
of normal substances. This is connected with the high critical 
‚Because v, 
pressure of water, being 198 atm., whence can be calculated, that 
the critical pressure — if water continued to consist of only double 
molecules — would yet still amount to circa 66 atm, i.e. higher than 
that of most of the normal substances. [Of course the designed express- 
Vartan 
ion will inerease with decreasing values of v, only when tee aa 
1 2 
that is to say, when the critical pressure of the first component is 
greater than that of the second. This condition will nearly always 
be satisfied, when we assume water as the first component |. 
As said, the decrease of v, is very considerable in the case of 
water. I remember, that I found some years ago’), that for 18 Gr. 
water v, = 19,78 cem., when all the molecules are double ; and only 
— 11,54 eem. for 18 Gr., when all the molecules are single. When 
therefore the temperature increases from nearly 90° C., where all 
the molecules are double (supposing, that the water had not congealed 
long before), to cirea 230° C., where all the molecules have become 
single, then v, will diminish down to nearly * 
|, of its original 
value. 
{In the same Memoir I showed, that in this fact lies also the 
explication — qualitative as well as quantitative — of the well- 
known phenomenon of maximum density at 4° C,| 
Now the consequence of this variability of v, will be, that the 
second member of (7) — we will represent it (divided by R) in 
DZ. f. Ph. Chemie 34 (Jubelband vay ‘rt Horr), p. 1—16, specially p. 13, 
