FREEZING POINTS OF NUTRIENT SOLUTIONS 



349 



mined in each case by reference to a reading of the freezing 

 point of the pure solvent, made with approximately the same 

 external temperature as obtained at the freezing point determi- 

 nation of the solution itself. 



The solutions to be tested were prejiared in the same manner 

 as were those emploj^ed by Tottingham, ''Baker's analyzed" 

 chemicals being again used. The distilled water was obtained 

 from the same still as was employed by that writer. Thus the 

 results here obtained from cryoscopic determinations are quite 

 comparable with Tottingham's calculated diffusion tensions. 



TABLE I 



Data showing the relation of external temperature to the 

 magnitude of the depression of the freezing poiint. as deter- 

 mined with the Beckmann apparatus, and to that of the depres- 

 sion corrected for undercooling, and the derived diffusion 

 tension at the freezing point. 



All of the solutions in Tottingham's optimal series (calcu- 

 lated diffusion tension 2.50 atmospheres, calculated total con- 

 centrations 0.6%) were subjected to cryoscopic test, as were also 

 those solutions of his supra-optimal series (calculated diffusion 

 tension 8.15 atmospheres, calculated total salt concentration 

 2.0%) which produced no precipitation on standing.^ A suffi- 

 cient number of the solutions in the remaining sub-optimal series 

 (calculated diffusion tension 0.05 atmospheres, calculated total 

 salt concentration 0.01%) were studied to demonstrate practical 

 agreement between Tottingham's calculations and the present 



* Tottingham {loc. cil., p. 222) calls attention to the fact that precipitates 

 occurred in 19 of these solutions, and these were therefore omitted in the present 

 studv. 



