UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 259 
aiw possibility of interference witli each otlier, even though 
the same reagent was employed. 
The following substances were employed as tests during 
the investigation : — 
1. Common Salt. 
2. Ammonium Sulphate. 
3. Metliylene Blue. 
4. Fluorescein. 
1. Common salt was introduced in quantities of half 
a ton at a time, and the issuing waters were tested quantita- 
tively for clilorine by means of a standard solution of nitrate 
of silver, the end reaction being observed by means of potassium 
chromate. 
Similar tests were made on the water issuing from the 
springs prior to the introduction of the salt, in order to ascertain 
the normal amount of chlorine present in each case. 
Curves were then drawn to indicate the fluctuation of the 
chlorine percentage during such period as was thought necessary 
by the Committee. 
This was found to be a satisfactory method, except in that 
it involved much labour in collecting and testing samples as 
well as in the transport of the salt to the sinks, many of which 
are situated on the hill sides, distant from any road or even 
track. 
2. Ammonium sulphate was employed in quantities of 
about 5 cwt., the springs being tested by means of Nessler's 
solution. In this case also " blank tests " were made before 
the introduction of the ammonium sulphate. 
This method possesses all the disadvantages of the fore- 
going, with the additional one that the quantity of ammonia 
in streams flowing through an agricultural district varies with 
changes of weather. 
There are one or two instances in this district in which 
every large shower carries the washings of a farmyard into the 
neighbouring stream, raising its ammonia percentage consider- 
ably, and thus rendering the tests with ammonium sulphate 
less certain in this area. 
