14 
been shown that during 1921 both causes operated and in the 
same direction, but evidence of extra-salt tides was not imme- 
diately forthcoming. Following the results obtained by the 
first set of analyses the Lake was emptied of water and refilled 
several times from the river. Analysis then showed that the salt 
content had been reduced to 0-424 grams per 1000 cc. of water. 
The first tidal barrier in the Thames is at Richmond, where 
the lock and weir are usually manipulated as a half-tidal barrier, 
the first full lock being at Teddington. Samples of water were 
obtained from above Richmond Lock at high and low tides and 
contained respectively 0-2 (3.10.21). and 0-1 (16.9.21.) grams of 
salt per 1000 cc. of the samples. There was thus only a slight 
difference in salt-content between the surface river water at 
high-tide at Kew and at Richmond. Indeed the Richmond 
water, as analysed, contained slightly the more salt, but that is 
explained by small variations noted for different tides throughout 
the course of the work. A sample collected from the Thames at 
Hampton Court (3.10.21.) contained 0-117 grams of sodium 
chloride per 1000 cc., that is, practically the same as the water 
at low tide at Richmond. 
In order to determine if the mud of the Lake held any con- 
siderable quantity of salt, known weights of wet mud were 
stirred with known volumes of cold and hot distilled water 
respectively. With cold water 0-585 grams of salt were extracted — 
from 1000 grams of mud, and with hot (boiling) water 0-83 grams. 
The amount of water held in the mud (‘‘ mud-water ”’) was then 
found by experiment, and by calculation 1-38 grams of salt was 
shown to be associated with 1000 grams of mud-water. This 
calculation on the ‘“ mud-water ”’ basis shows, of course, a richer 
salt content than the calculation on the basis mud plus water 
(“ wet-mud ”’). There seems every probability that during the 
latter part of the summer the mud and water left behind when 
the lake was drained as far as possible, contained enough salt 
to affect temporarily the next supply of water, but insufficient 
to be considered a permanent cause of salinity. 
It was not: till the week ending November 5th that definite 
evidence of extra-salt tides was “ptcned. During the week 
very high tides were experienced in the Thames estuary. Two 
samples taken at Kew contained 1-14 grams of sodium chloride 
and 1-2 grams per 1000 respectively, as compared with 0-15 
grams per 1000 which appears to be about the average salinity 
of the Thames water at Kew. During these very high and 
extra-salt tides fresh water fish (barbel) came to the surface and 
sides of the river in shoals. They showed obvious signs of being 
affected by the incoming tide and many were caught with the 
hands or in hand-nets 
The conditions which cause the increased salinity of the Kew 
water have thus been shown to be due directly to the drought 
