AS INDICATED BY OSMOMETERS. 55 



surface to be studied (at any chosen depth), and the rate at which 

 water was osmotically absorbed might be read on a suitable graduated 

 tube, the latter connected with the cell across one side of which the 

 membrane was stretched. After a number of failures, such a device 

 was obtained, and, while the experimentation was necessarily curtailed 

 by lack of time, the results obtained from its use in connection with 

 several artificial soil mixtures seem to promise so much that they are 

 deemed worthy of presentation here. It is to be remarked that the 

 osmometer method here employed will surely be found susceptible of 

 much improvement ; our results are brought forward at this time rather 

 to show the possibility of deahng quantitatively with this much- 

 neglected environmental condition than for any other reason. 



The studies here reported were carried out at the Desert Laboratory 

 of the Carnegie Institution, at Tucson, Arizona, during the summer of 

 1913. The writers are indebted to the Director of the Department of 

 Botanical Research of the Carnegie Institution of Washington for the 

 facilities of the Desert Laboratory. 



METHODS. 

 PREPARATION OF THE OSMOMETERS. 



The osmometers employed were prepared from ordinary thistle tubes, 

 the large opening closed by a collodion membrane. When properly 

 formed this is found to be practically impermeable to cane-sugar, which 

 was the solute used in our cells. At the same time, these collodion 

 j51ms are permeable enough to water for the present purposes, and they 

 are somewhat readily prepared and arranged for operation.^ 



Our membranes were formed by evaporation of the solvent from a 

 solution of ''Schering's celloidin," dissolved in a mixture composed of 

 equal parts (by volume) of ether and alcohol. Absolute alcohol should 

 be used. We employed solutions containing from 7 to 10 grams of col- 

 lodion per 100 c.c. of the solution. When working at high tempera- 

 tures, as the sunamer temperatures of Tucson, it is perhaps advisable 

 to employ solutions as weak as with 7 or 8 grams per 100 c.c, on account 

 of the high evaporation rate. The collodion solution is poured on to 

 the surface of clean mercury in a shallow vessel of considerably greater 

 diameter than that required for the membrane. The solution is not 



^In connection with the use of collodion membranes in osmotic studies, and on the manipu- 

 lations required in their preparation, see the following papers : 



Bigelow, S. L., and A. Gemberling, Collodion membranes. Jour. Amer. Chem. Soc. 29: 1576- 

 89. 1907. 



Mathews, J. H., Osmotic experiments with collodion membranes. Jour. Phys. Chem. 14: 

 281-91. 1910. 



Smith, G. M., The use of collodion membranes for the demonstration of osmosis. Bot. Gaz. 

 56: 225-9. 1913. 



Abel, J. J., L. G. Rowntree, and B. B. Turner. On the removal of diffusible substances from 

 the circulating blood of living animals by dialysis. Jour. Pharmacol, and Exp. Therap. 

 5: 275-316. 1914. 



