JoLY — On a New Method of Gauging the Discharge of Rivers. 491 



This quantity of radium — pure — would cost about 36s. ; in the ore 

 it should be one-sixth or one-eighth part of this, i.e., five or six shillings. 



If a two per cent, determination was deemed sufficiently accurate, and a 

 fifteen-minute feed into the river, a hundred grams of ihe crude ore would 

 suffice, and the cost would be correspondingly reduced. 



As regards details, I propose to bring the pitchblende into solution by 

 powdering it and adding nitric acid. It dissolves readily. The charge is 

 then diluted with water up to about two gallons, i.e., the full of a petrol tin. 

 In this form it is brought to the scene of operations. The stopper is then 

 replaced by one which carries a copper tube dipping to the bottom of the 

 tin. This tube is coupled to a similar small-bore tube to be laid out across 

 the current. It is pierced with fine holes at intervals, say of 6 inches. Air 

 pumped into the tin by an ordinary tyre-pump serves to expel the liquid. 

 The current is steadied by having in circuit air indiarubber bag, which is 

 kept inflated to a constant pressure, as read by a small air-pressure gauge. 

 The air-pressure being considerable, the small effect of variation in 

 hydrostatic head will be negligible. 



I think a very little time spent on experiments in the laboratory will 

 suffice to bring these practical details into working order. 



When the samples are collected (each sample will about fill a petrol tin) 

 and brought back to the laboratory, they are stored in ordinary boiling 

 flasks for ten or twelve days. The emanation is then boiled off, being 

 caught in a small exhausted bulb, from which it is introduced into the 

 electroscope. At the end of three hours the electroscope is read, and the 

 river discharge is then immediately deducible. If thought desirable, the 

 samples may be evaporated down to any required extent. No error is 

 introduced by this process. It is necessary lo carry out these operations in 

 a laboratory free from radium contamination. 



