468 Dr. M.Wilclermann on Real and Apparent 



determined with ice, when it has almost completely melted, 

 belong to the less accurate ones. Not only is the value of 

 to — t-ov thus made at the freezing-temperature exceedingly 

 small, and consequently the experimental error exceedingly 

 great, but the remaining quantity of ice cannot be strictly 

 regulated, and this means 1 — t ov , and with it the experimental 

 error, can easily be in one experiment a multiple of the other. 

 Moreover, ahead}' with a quantity of ice even =0°'l or o, 2 

 overcooling, no good equilibrium between ice and the liquid 

 can be practically established, i. e. no constant apparent 

 freezing-point can be obtained. For the correction for the 

 separated ice see P. B. Lewis, Trans. Chem Soc. 1894. 



Putting for dilute solutions C = (7, K^K/, and arranging 

 t — t ov =t ' — t ov ', we obtain from (A") 



,'-*»=,-,/+! [ft-v>-(''-'">] , . (A », 



JV/ t t ov 



and from this it follows : — 



(1) If t g is put =t g ', then we obtain 



+/ tii — t t ' (^ ~0 



I t<0~~ "O -TT . . 



-Ely to ~~ tov 



or 



(i+E^y-'") = «.-«.'; 



that is to say, at a constant convergence-temperature the 

 apparent freezing-point depressions will be in all concentrations 



r^j smaller than the real. 



1 + 



"-/\*0 t ov ) 



(2) Now t g is practically always more or less different 

 from tj. The variations of the ice-bath lead through this to 

 experimental error in the more as well as in the less dilute 



Q (f —t ') 

 solutions, which is = ^ —^ — ^2. 



IVy t t 



It is clear that in dilute solutions in which t' — t" is small 

 compared with t g — t g ', the latter is only to be taken into 

 account in our consideration of the experimental error, and, 

 going over to more concentrated solutions Avhere the depres- 

 sions t'—t" become of greater importance, t g —t g ' — {t' — t") 

 must be kept as nearly as possible equal to ; i. e., in dilute 

 solutions we have the following rule for the freezing-point 

 method : — the same convergence-temperature, the same tempe- 

 rature of the bath at the same temperature of the room ; and, 

 in more concentrated solutions, again, the other rule becomes 



