2 Mr. J. J. Coleman on Liquid Diffusion. 



Watts's c Dictionary of Chemistry/ vol. iii. p. 710. Graham, 

 however, in his latest paper upon the subject, communicated 

 to the Royal Society in 1861, described a method of experi- 

 ment which, to use his own words, affords a means of obtaining 

 the absolute rate or velocity of diffusion. This he called " Jar 

 diffusion," the saline solution being delivered by a pipette to 

 the bottom of a column of pure water 127 millim. high, stand- 

 ing in a cylindrical jar 87 millim. diameter, and the amount 

 diffused being ascertained by drawing off the liquid from the 

 top in equal fractions by a very fine syphon, the orifice of the 

 short leg of which was kept close under the surface of the 

 liquid being drawn off. 



Graham applied this method to a variety of organic com- 

 pounds, but only to hydrochloric acid, sulphate of magnesia, 

 and sulphates and chlorides of potassium and sodium amongst 

 inorganic substances. He did not attempt the calculation of 

 the coefficients of diffusibility in absolute measurements, but 

 remarked that the method is extremely simple, and gives results 

 of more precision than could have been possibly anticipated. 



I have recently made a considerable number of experiments 

 with this method ; but in place of using jars of 87 millim. in 

 diameter I have employed glass cylinders of 36 millim. dia- 

 meter, such as are used for " Nesslerizing," and which are 

 very uniform in bore. The annexed Table shows the actual 

 amount of salt found in each section of the liquid after dif- 

 fusion, expressed in millimetres ; the quantity of salt in the 

 upper section being also calculated in percentages of that 

 particular section which at the commencement of the dif- 

 fusion was the point of junction of the saline solution and the 

 pure water. 



The concentrated saline solution was introduced below the 

 pure water by a method slightly different to that of Graham ; 

 namely, a fine -bore syphon with contracted orifices was first 

 filled with water, the finger being placed so as to cover the 

 short end ; the long end was thrust to the bottom of the water 

 in the diffusion-jar, and the short end was uncovered in a 

 vessel containing the saline solution at a higher level, and the 

 syphoning continued until the height of the liquid admitted 

 under the water in the diffusion-jar amounted to 50 millim. 



Many of the results agree with those of Graham, whilst 

 others are additions thereto, such as the diffusions of mercurous 

 nitrate, mercuric chloride, lithium sulphate, cadmium sul- 

 phate, silver sulphate, manganese sulphate, nickel sulphate, 

 and lead nitrate. 



Moreover they are twenty-five diffusions conducted for 

 equal lengths of time, and under similar circumstances as to 

 temperature and methods of experimenting. 



