252 Proceedings of the Royal Irish Academy, 
ture until perfect deliydration takes place. It is evident, also, tliat in 
the salts tried perfect dissociation takes place at a higher point than 
the boiling point of water, when operating at ordinary pressnre, and 
except we are dealing with very concentrated solutions. It then 
becomes difficult to determine how far dissociation of the more ulti- 
mate molecules may play an exceptional part in the decomposition. 
Lastly, we also perceive that dilution raises the thermanalytic point 
as regards the molecules of hydration. 
XXX. — On the Ploatation of Sand on the Kivee, Ganges. By Mr. F, 
X. J. "Webber, in a communication to Henry Hennessy, F. E. S.^ 
Vice President of the Academy. 
[Read 8th April, 1872.] 
[In making this communication to the Academy, Professor Hennessy 
referred to his Paper on the Tloatation of Sand by the Rising Tide in 
a Tidal Eiver, read on April 10, 1871, and especially to his anticipa- 
tion that tropical regions of the earth would present favourable condi- 
tions for the occurrence of similar phenomena. This anticipation was 
immediately verified during the discussion which followed, when Dr. 
E. Perceval Wright mentioned facts that came under his observation 
during his voyage to Mauritius and the Seychelles Islands. 
The remarkable instance of sand floatation now brought under the 
notice of the Academy differs from those hitherto mentioned, in the 
circumstance that it occurred in fresh water, and its geological im- 
portance is enhanced by the magnitude of the river where it took 
place.] 
I remember often having seen sand floating on the Ganges and its 
larger tributaries. On one occasion I remember plunging my hand 
into the water, and taking it up, coated with what I at first thought 
was sawdust, but found on close inspection to be sand. I had observed 
the thin crust floating on the surface of the river, and went to clear a 
space, I forget for what purpose. The banks of the river at that place 
were low and sandy ; in fact there was no vegetation for about twenty 
yards inland on each side of the stream. The sand itself was too hot 
to be borne on the hack of the hand. 
The presence of the sand on the water was, I think, owing to un- 
dermining of the banks of the river (a process, as you are well aware, 
continually going on in all the large rivers of India), the falling por- 
tions sometimes striking the water with considerable force, at other 
times sinking so gently into the river as not even to cause a splash or 
a ripj)lc. It was, of course, a very hot day, with scarcely a breeze ; I 
need not say there wasn't a cloud in the sky. 
The sand appeared to form a thin crust on the surface of the river; 
I do not remember remarking pebbles or shells in it. ' 
I am positive there was no decayed vegetable floating on the nver, 
