Mr. T. Graham on Liquid Diffusion applied to Analysis. 293 



millimetre, or ^TTT °^ a mi Ui metre - Wet parcliment-paper so 

 thin is highly translucent. Gelatinous starch, slightly coloured 

 with blue litmus, was applied by a brush to one side of the wet 

 parchment- paper. Immediately afterwards a drop of water, 

 containing yoVo-th. part of hydrochloric acid, was applied on 

 the point of the finger to the other (the lower) side of the 

 paper. The time required by the acid to affect the litmus, in 

 five successive trials, was 6 seconds, 5*5 seconds, 6 seconds, 

 and 5 seconds. The mean is 5*7 seconds, which is therefore 

 the time required by hydrochloric acid, diluted already 1000 

 times, to travel a distance of 0*0877 of a millimetre, by the agency 

 of diffusion. The temperature was 15°. 



With hydrochloric acid diluted twice as much as before (water 

 containiug 0*0005 dry acid), the average time of passage was 

 10*4 seconds, or nearly double the preceding time. 



Water containing y^-^-th of sulphuric acid (an acid less rapidly 

 diffused than hydrochloric acid) reddened the litmus in 9'1 se- 

 conds, and when doubly diluted, in 16*5 seconds. 



These results are not affected, it is believed, by any sensible 

 diffusive movement on the part of the litmus. The diffusion of 

 that colouring matter, in a colloid medium, is so slow that it may 

 be entirely disregarded. The acid, therefore, is not met in its 

 way by the litmus, but really travels the entire distance expressed 

 by the thickness of the parchment-paper. The first experiments 

 related give a diffusive velocity, in water, to hydrochloric acid, 

 already diluted one thousand times, of 0*0154 millimetre per 

 second, and 0*924 millimetre in one minute. 



The few following dialytic experiments may be recorded for the 

 sake of the practical points which they bring out. They were 

 made in the smaller osmometer, with 100 cub. centims. of a solution 

 containing 10 grammes of each of the various substances. The 

 area of the parchment-paper septum was 0*005 square metre, and 

 the depth of the stratum of fluid placed upon it 20 millimetres. 

 The substances diffused were all crystalloids, with the exception 

 of gum-arabic. 



Table XII. — Dialysis through Parchment-paper during 

 twenty-four hours, at 10° to 15°. 



Diffusate, 



Relative 



Osmose, in 



Relative 



in grammes. 



diffusate. 



of water. 



osmose. 



0-029 



•004 



5-0 



•263 



2-000 



•266 



17-0 



•894 



1-607 



•214 



15-3 



•805 



1-387 



•185 



15-0 



•789 



2-621 



•349 



17-6 



•926 



3-300 



•440 



17-6 



•926 



3-570 



•476 



7-6 



•400 



2-130 



•284 



16-8 



•884 



7-500 



1 



19-0 



1 



Gum-arabic , 



Starch-sugar 



Cane-sugar 



Milk-sugar 



Mannite 



Glycerine 



Alcohol 



Starch-sugar (second experiment) 

 Chloride of sodium 



