DixoN AND Ma80N — Cijinncopic Melhod fov Estimation oj Sucrose. 7 



As soon as the saps had taken up the temperature of the bath, 0'33 gm. 

 of invertase solution was added from a capillary tube. The sap-invertase 

 solutions were then inoculated with a little hoar frost and their freezing- 

 points determined. After storage overnight at 28°, the depressions were 

 again observed. That inversion was complete was ascertained by raising to 

 boiling-point as before, and again determining the freezing-points. In 

 Table V are shown the depressions of the sap-invertase solutions before and 

 after inversion. The difference in the observed depressions have been 

 corrected for the dilution due to the addition of the invertase solution ; in 

 the final column are shown the equivalent concentrations of sucrose.'^ It 

 will be observed that no correction has to be made for the solutes introduced 

 with the invertase solution. It is of great importance that the saps should 

 be cooled below 0° before the addition of the invertase, or otherwise 

 immediate inversion will take place, and the results obtained will be 

 too low. 



Table \. 



Deflection of Thermo-couple, 1617 mm. per 1°. 



A consideration of importance in favour of the cryoscopic method is the 

 absence of any preliminary treatment for the purpose of clearing the sap of 

 gums, etc.; this treatment is, of course, necessary before polarimetric or 

 copper methods can be employed. 



It is, however, for work in relation to the osmotic pressure in plants that 

 tlie method has been elaborated, and is especially applicable. 



An approximate comparison of the delicacy of the cryoscopic method 



' Tlie vaiue.s here assigned to the increase in depression are based on the assunijition 

 that the freezing-point depression of sucrose is exactly doubled on inversion ; this is not 

 true to the thousandth of a desrrei;. 



