350 CARNEGIE INSTITUTION OF WASHINGTON. 



failure of our earlier efiorts to ''recover" cells are obscure; but during 

 the past year Dr. Holland and his associates have overcome the 

 difficulty by subjecting the membranes to be removed to a very slow 

 process of electrolytic decomposition and removal by solution, and 

 afterwards re-burning the cells. 



Dr. Holland and Messrs. Blocher and Minter have carried out a 

 complete series of measurements of the osmotic pressure of levulose 

 at 30°. This work had been begun previous to the writing of the last 

 report, but during the past year the earlier experiments were repeated 

 and the measurements on all concentrations from 0.1 to 1.0 weight- 

 nonnal solutions were completed. The conclusion reached is that 

 (as in the case of dextrose) the ratio of osmotic to the calculated gas 

 pressure of the solute is constant for all concentrations of solutions 

 of levulose up to 1.0 weight nonnal. On the other hand, the hydra- 

 tion of the solute, which is supposed to explain the excessive pressures 

 of both dextrose and levulose at low tenperatures, was found to be 

 somewhat more persistent in the case of the latter than in that of the 

 former. At 30° the ratio in question is uniformly unity for dextrose 

 and about 1.02 for levulose. 



Attempts were made during the year to resume the measurement 

 of the osmotic pressure of cane-sugar solutions at high temperatures 

 (above 40°), but without much success, owing m part to a recurrence 

 of what has been called the " Penicillium pest." 



At somewhat elevated temperatures cane sugar soon begins to 

 invert in the cells. If the cell "works rapidly," i. e., if the osmotic 

 pressure rises quickly to a maximum, a measurement may be secured 

 before the inversion reaches a significant magnitude. It is therefore 

 impracticable to employ with cane sugar at elevated temperatures 

 any but fresh membranes of large area. This slow inversion, which 

 is observed in cells at the higher temperatures, is perhaps promoted, 

 if not caused, by the presence in the solutions of a minute quantity 

 of the membrane material; for it has been observed that portions of 

 the same solutions, maintained outside of the cells at the same tem- 

 peratures, and for the same length of time, do not, if properly pro- 

 tected, exhibit inversion. 



The liability to "penicillium infection" is always impending, and 

 the presence of the spores in the air is one of the great obstacles in 

 the way of the measurement of osmotic pressure. These penicillia — 

 said by our experts who have studied them to some extent to be of 

 various "strains" — attack the membranes with great voracity, 

 probably because of their nitrogen content, and unless they are quickly 

 checked they soon destroy the membranes. Our methods of avoiding 

 infection and of exterminating Pe7iicilliu7ti when, in spite of our 

 elaborate precautions, it has lodged in the cells and baths, have been 

 described elsewhere. The complete eradication of the pest usually 



