22 Proceedings of the Royal Irish Academy. 



of pebloles, wetted mth. salt water in the case of the salt-water experi- 

 ments and fresh, water in the case of the fresh-water experiments. 

 Eio-ht flasks were exposed in this manner, each to an equal stream of 

 ' air four containing fresh water, and four sea-water. The duration 

 of the experiments was three months, during which time the current 

 of air continued, with only a very few days intei-mission, both during 

 night and day. On each occasion upon which the flasks were shaken 

 it was found that the salt-water solutions had almost cleared before 

 the next day, whereas the fresh-water solutions remained turbid, a 

 natural effect, which in nature is of much importance. 



The second mode of experiment was applied to a specimen of the 

 basalt only. In this case the material in coarse grains and fragments, 

 to the weight of about 180 grammes, is placed in a U-tube, and by a 

 cup -of -Tantalus arrangement, which will be described in the appendix, 

 the solvent (which in this case also was 1000 c.cs. in volume) was 

 compelled to travel in opposite directionsthrough the tube, passing from 

 an Erlenmeyer Jena-glass flask placed beneath to one placed above, 

 and gravitating back again, continuously duiing the daytime. The 

 air from the room enters through damping tubes into the upper and 

 lower flasks alternately with the withdrawal of the solvent. 



The action upon the material in the U-tube may be considered as 

 much like what goes on upon the sea beach or in the wash of a river, 

 for at the completion of each upward passage of the water through 

 the U -tube one limb of the tube is to a considerable extent drained 

 of water, air entering freely between the coarser particles. On the 

 completion of the downward movement the other Limb of the tube is 

 drained out to a large extent. The particles are thus exposed to the 

 wash of the solvent in both directions, and to its periodic partial 

 withdrawal from around them. There is, however, no attrition. 



The time occupied in the upward passage of the water is from 

 •seven to eight minutes ; in the downward from about eight to nine 

 minutes. The flasks and U -tubes are in duplicate, the U -tubes being 

 attached side by side, the one holding basalt traversed by salt water, 

 and the other basalt traversed by fresh water, and the current is 

 maintained through each by the one hydraulic arrangement. 



The duration of this experiment was foui- months. At night the 

 active motion of the water was stopped, but during this period the 

 particles remained submerged. 



Surface Area exposed to Solution. — It is very certain that the rate 

 of motion of the solvent in such experiments has within limits only a 

 minor influence on the ultimate results. It is even doubtful if the 



