94 OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



various ways, but without entirely satisfactory results. One of the 

 modifications consisted in the omission of both the caustic potash and 

 the hydrochloric acid, and in the removal, by electrolysis, of the soluble 

 salts which were left in the wall after soaking the cell in water. The 

 best results were obtained by a simple electrolysis of the membranes 

 in the presence of water, but the removal of membranes by this method 

 is exceedingly slow. Fairly good results were also obtained by grind- 

 ing off the interior wall of the cells with a carborundum wheel running 

 at high speed, and afterwards reburning them. In whatever manner 

 the membranes may be removed, the reburning is essential. It is 

 suspected that the walls of the pores, near their mouths, are in some 

 way modified (perhaps made more smooth) by the reagents which are 

 employed to remove the membranes, with the result that the "plugs" 

 of the new membranes do not fit so firmly into their places. It is now 

 preferred to discard cells with old or defective membranes rather than 

 attempt to restore them to use by replacing their membranes. 



9. INFECTION OF THE MEMBRANES. 



The ready infection of the membranes by voracious nitrogen-con- 

 suming fungi has been one of the serious obstacles to the progress of 

 the present investigation. The particular fungus known to have pro- 

 duced a large amount of mischief is a strain of Penicillium glaucum. 

 Others are believed to have contributed to the frequent destruction 

 of the membranes, but they have not been identified with certainty. 



The first announcement* regarding this pest was as follows: 



"Soon after beginning the measurement of osmotic pressure, there appeared 

 upon one of our cells an abundant growth of a fungus, which upon examination 

 was found to be penicillium. Within the next few clays, it appeared upon one 

 after another of the remaining cells, until all were affected in the same manner 

 as the first. We then exposed several solutions of glucose to the air of the 

 laboratory, and the fungus appeared in all of them in a short time. We had 

 had no similar experience previously, though we had worked with solutions 

 containing invert sugar more than two years, and the conditions under which 

 we were working were in general unfavorable to the fungus. The sudden 

 prevalence of penicillium spores in the atmosphere of the laboratory could, 

 however, be accounted for, though it had not been anticipated. At the time, 

 certain changes were in progress in the lower part of the building which 

 involved the tearing away of old walls, and the atmosphere of all parts of the 

 laboratory was, in consequence, in a somewhat dusty condition." 



A search was immediately instituted for some poison which would 

 kill the fungus without injuring the membranes. Of the numerous 

 substances which were tested, hydrocyanic acid in gaseous form and 

 thymol were found to be quite effective and entirely harmless to the 

 membranes. Formaldehyde has also been extensively employed, espe- 

 cially for the disinfection of the baths. 



*Amer. Chem. Journal, xxxvi, 34. 



