214 OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



DETERMINATIONS OF THE OSMOTIC PRESSURE OF LITHIUM CHLORIDE AT 30°.* 



It has been observed that the lithium salts appear to be much less 

 harmful to the membranes than those of potassium. Abundant evi- 

 dence of this will appear in the following record of the determina- 

 tions of the osmotic pressure of lithium chloride solutions, ranging in 

 concentration from 0.1 to 0.6 weight-normal. The superior resistance of 

 the membranes to salts of lithium is possibly due to the large atmos- 

 phere of water with which the cation is supposed to be surrounded. 



The determinations of the osmotic pressure of lithium chloride here 

 recorded are not regarded as "final," because it was not demonstrated 

 that the solutions maintained perfectly their concentration while in the 

 cells. They will, therefore, be repeated at a later date when an "inter- 

 ferometer" is available for the purpose of detecting and measuring 

 slight differences in concentration. They are believed, however, to be 

 very nearly correct. All the water in which the cells had stood during 

 the experiments was examined for the presence of chlorine. In every 

 case a slight milky appearance was produced bj^ silver nitrate, but the 

 quantity of chlorine thus precipitated did not in any instance exceed 

 2 milligrams per 100 cubic centimeters of the solution, and that amount 

 could be accounted for as due to a slight unavoidable soiling of the cell 

 while filling it with the solution. The reasonableness of this explana- 

 tion was confirmed by the fact that the quantities of chlorine found 

 bore no definite relation to the duration of the experiments. After 

 leakage, the most frequent cause of a change in the concentration of 

 the cell contents is, as previously stated, an improper adjustment of 

 the initial pressure. But such adjustments give very little trouble, 

 except at high temperatures, and they are not believed to have affected 

 the concentration of the solutions of lithium chloride at 30°. A third, 

 but at present infrequent, cause of dilution or concentration of the cell 

 contents has not been previously mentioned. It depends on the use 

 of rubber in closing the cells. The employment of this material is, 

 unfortunately, essential to the proper adjustment of initial pressure, 

 but its use carries with it the danger that, through its movements under 

 pressure, the capacity of the cell, and therefore the concentration of the 

 solution, may be altered. The movement of the rubber may be inward, 

 and result in concentration; or outward, and result in dilution. Every 

 effort is made to confine the rubber in such a manner as to reduce its 

 possible movements to the limits essential to the proper adjustment of 

 initial pressure, but the means of effecting this has always been one of 

 the more perplexing mechanical problems of the present investigation. 

 If the solutions of lithium chloride failed to maintain perfectly their 

 concentration, it was probably due to some imperfect confinement of 

 the rubber which was employed in closing the cells. 



♦Measurements by H. N. Morse, J. C. W. Frazer, and E. L. Frederick. 



