Mr. T. Graham on Liquid Diffusion applied to Analysis. 209 



the same by heat. Mr. De la Rue recommends the use of albu- 

 men in cementing parchment-paper, which thus may be formed 

 into cells and bags very useful in dialytic experiments. The 

 mixed fluid to be dialysed is poured into the hoop, upon the sur- 

 face of the parchment-paper, to a small depth only, such as half 

 an inch. The vessel described {dialyser) is then floated in a 

 basin containing a considerable volume of water, in order to in- 

 duce egress of the diffusive constituents of the mixture. Half a 

 litre of urine, dialysed for twenty-four hours, gave its crystal- 

 loidal constituents to the external water. The latter, evaporated 

 by a water-bath, yielded a white saline mass. From this mass 

 urea was extracted by alcohol in so pure a condition as to appear 

 in crystalline tufts upon the evaporation of the alcohol. 



1. Jar Diffusion. 



The mode of diffusing more lately followed, which I have 

 already alluded to as jar diffusion, is extremely simple, and gives 

 results of more precision than could possibly be anticipated. 

 The salt is allowed to rise from below into a cylindrical column 

 of water, and after a fixed time, the proportion of salt which has 

 risen to various heights in the column is observed. The water 

 was contained in a plain cylindrical glass jar, of about 152 milli- 

 metres (6 inches) in height and 87 millimetres (3*45 inches) in 

 width. In operating, seven-tenths of a litre of water were first 

 placed in the jar, and then one-tenth of a litre of the liquid to 

 be diffused was carefully conveyed to the bottom of the jar by 

 means of a fine pipette. The whole fluid column then measured 

 127 millimetres (5 inches) in height. So much as five or six 

 minutes of time were occupied in emptying the pipette at the 

 bottom of the jar, and extremely little disturbance was occasioned 

 in the superincumbent water, as could be distinctly seen when 

 the liquid introduced by the pipette was coloured. The jar was 

 then left undisturbed, to allow diffusion to proceed, the experi- 

 ments being always conducted in an apartment of constant, or 

 nearly constant temperature. When a certain time had elapsed, 

 the diffusion was interrupted by drawing off the liquid from the 

 top, by means of a small siphon, slowly and deliberately, as the 

 liquidhad been first introduced,in portions of 50 cubic centimetres, 

 or one-sixteenth of the whole volume. The open end of the short 

 limb of the siphon was kept in contact with the surface of the 

 liquid in the jar, and the portion of liquid drawn off was received 

 in a graduated measure. By evaporating each fraction separately, 

 the quantity of salt which had risen into equal sections of the 

 liquid column was ascertained. From the bottom of two jars, 

 A and B for instance, a 10 per cent, solution of chloride of sodium 

 was diffused for a period of fourteen days. The whole quantity 



Phil Mag. S. 4. Vol. 23. No. 153. March 1862. P 



