234 Intelligence and Miscellaneous Articles. 



with great accuracy. For diaphragm I took successively parch- 

 ment paper, bladder, and a porous vessel of unglazed porcelain. 

 The results obtained show that the ratios between the quantities 

 of liquid which pass through and the mean pressures are constant ; 

 that is, whatever be the liquid, the quantity which passes through 

 in a given time is proportional to the mean pressure, alcohol not 

 excepted. 



I have found that, during the filtration, the outside of the porous 

 vessel becomes covered with bubbles proceeding from the air con- 

 tained in the water and in the diaphragm, which is disengaged in 

 passing through the latter in consequence of the capillary affinity 

 exerted by it upon the liquid. These bubbles, more or less obstructing 

 the pores, render the filtration irregular — an inconvenience which is 

 in great part got rid of by working with distilled water from which 

 the air is expelled by boiling. But this is not the only error to be 

 avoided ; the inequality of calibre in different parts of the length of 

 the tube is another for which allowance must be made. These two 

 causes are sufficient to account for the difi'erences which have been 

 observed. 



The following coefficients were found to express the ratios between 

 the mean pressures and the quantities of liquid filtered through a 

 porous porcelain diaphragm in half an hour with the same filtering 

 surface :— 



Hydrochloric acid 0'187 



Distilled water 0"165 1 increased by their 



Ammonia 0'139 J volume of water. 



Chloride of calcium in solution at 35° 0'055. 



The experiments were made at temperatures varying from 15° to 

 20°. It is to be remarked that, when experimenting with bladder, 

 after a certain number of hours the cells are distended and the 

 coefficients progressively increase until they become double ; with 

 vessels of porous porcelain nothing of the kind happens ; the course 

 of the flow is regular. 



Other solutions were also submitted to experiment ; but in this 

 abstract I shall only mention the results obtained with a solution of 

 sulphate of soda and another of sulphate of lime, both concentrated 

 and deprived of air, and giving rise by their reaction to an insoluble 

 crystallized precipitate. 



*I have shown, in a previous memoir, that when a solution of 

 nitrate of lime is introduced into a tube closed at the lower end with 

 parchment paper, and the tube dips into a test-glass containing a 

 solution of sulphate of soda, we soon see form on the surface of the 

 diaphragm in contact with the sulphate solution, and also in that 

 solution, a very great number of fistular stalactites of crystallized 

 sulphate of lime, which little by little lengthen until they reach the 

 bottom of the test-glass, where the substance spreads out. 



I then worked in the opposite direction : I poured into the tube 

 containing the liquid exerting the pressure a solution of sulphate of 

 soda, and the nitrate-of-lime solution into the test-glass, in order to 



