PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
807 
Hydrochloric acid belongs to the most diffusive class of substances known ; it ap- 
pears to exceed hydrate of potash at 53°‘5, as 7'50 to 6' 12, or as 100 to 80’9^. 
The rapidity with which hydrochloric acid diffuses, and the facility with which that 
substance may be estimated, induced me to examine the progression with which its 
diffusion takes place with increasing times in a minute manner. The 2 per cent, solu- 
tion was diffused for times increasing by six hours, from twelve hours or 0*5 day to 
4‘75 days, six cells being diffused for every period. Instead of determining the acid 
diffused separately in each jar or pair of jars, the contents of the six jars of each ex- 
periment were mixed together, and a definite proportion of the liquid precipitated by- 
nitrate of silver, so as to obtain at once the mean result. Another observation for 
5‘75 days is added, although made at a sensibly higher temperature. 
Diffusion of Hydrochloric Acid, 2 per cent, solution ; one cell. 
Time. 
Temperature. 
DLfFusate in grains. 
Differences. 
days. 
0*5 
53*75 
0*909 
0-75 
53*75 
1*312 
*403 
1 
53*75 
1*766 
*454 
1*25 
53*75 
2*353 
*587 
1*5 
53*75 
2*596 
*243 
1*75 
53*58 
3*178 
*582 
2 
53*58 
3*410 
*232 
2*25 
53*42 
3*967 
*557 
2*5 
53*58 
4*339 
*372 
2*75 
53*50 
4*618 
*279 
3 
53*50 
4*969 
*351 
3*25 
53*50 
5*304 
*335 
3*5 
54*85 
5*857 
*553 
3*75 
54*85 
6*254 
*397 
4 
54*85 
6*407 
*153 
4*25 
54*85 
6*795 
*388 
4*5 
54*71 
7*034 
*239 
4*75 
54*71 
7*473 
*339 
5*75 
56*46 
8*363 
The differences are evidently affected by accidental errors of observation. The 
diffusion at 3‘5 days is also increased by a rise of temperature of more than 1° in that 
and the following experiments. The diffusion always increases with the time, but less 
rapidly, according to a gradually diminishing progression. 
2. Hydriodic Acid, Hydrohromic Acid and Bromine. 
Hydriodic Acid . — Time of diffusion five days, as for hydrochloric acid. The acid 
diffused was estimated from the iodide of silver whieh it gave when precipitated by- 
nitrate of silver. 
Hydriodic acid, T98 per cent.; density 1-0142. Diffused at 53°-5, in eight cells, 
14-90, 15-67, 15-25, 15-27 ; mean 15-27 grs. for two cells. Calculated for 2 per cent., 
15*42 grs. at 53°-5 for two cells, or 15-11 grs. at 51°. 
* Philosophical Transactions, 1850, p. 39. 
