92 



MR. W. E. BALDWIX-WISEMAX OX 



[Feb. 1907, 



Before leaving the question of flow, it may be of some interest to 

 record the mode of rupture of the chalk in the course of the ex- 

 perimental investigations. At pressures of about 35 lbs. per square 

 inch, pieces broke away from the under surface of the test-piece, 

 leaving an apparently-dry surface, showing that the rupture was 

 sudden ; for soon thereafter the percolating water spread over the 

 whole surface in a moist film, on which the drops gathered before 

 dropping into the collecting-pan. As the pressures were increased, 

 other pieces of lesser size detached themselves from time to time, 

 until at a pressure of 46 lbs. per square inch, the test-piece cracked 

 near the centre of the unsupported circle of rock, through which 

 crack an irregular jet of water passed. By introducing coloured 

 water into the cylinder, I was able to stain the surfaces of this 

 crack ; and, upon breaking up the test-piece, I found the crack to be 

 irregular, but approximately vertical. Other test-pieces of chalk 

 gave almost identical results, at similar or slightly higher pressures ; 

 and it is possible that chalk-cliffs may in part be destroyed by the 

 rupturing action of interstitial water at higher pressures than this. 

 In experimenting upon the rate of flow of various solutions 

 through capillary tubes, Girard (23) found that the rate of flow was 

 largely affected by the strength and temperature of the solution and 

 by the chemical composition of the dissolved salt. Thus, for instance, 

 the velocity through equal lengths of tubes of the same diameter 

 under the same difference of pressure varied, as shown in the follow- 

 ing Table (VII) : — 



Table VII. 



Maid. 



Strength of 

 solution. 



Tem%)erature 

 in°C. 



Relative velocity, 



compared with that 



of water at 60° C. 



as unity. 



Water 



1/6 



J? 



1/3 

 1/3 

 1/3 





 60 



8 

 80 



3 

 60 



3 

 60 





 60 



0875 

 1-000 

 0-774 

 2-907 

 0-465 

 1-653 

 0-678 

 2045 

 1-330 

 2-924 



Solution of sugar 





Solution of common salt . 

 Solution of saltpetre 



I conducted a series of observations on the flow of brine through 

 a block of Bath weatherstone under various pressures ; but the data 

 obtained were of little use, as neither the discharges nor the differ- 

 ence of density of the solution before and after percolating through 

 the block were at all constant under the same pressure, nor were 

 the variations at different pressures at all comparable one with 



