288 Messrs. F. Soddy and T. D. Mackenzie on the 



be too low or negative. In this experiment it is intended 

 to cany out tests but rarely, and to preserve the gas 

 pumped out. 



A fresh kilogram of uranyl nitrate from the manufacturer 

 was purified twice by extraction with ether, and first tested 

 on Nov. 28th, 1906. It gave a leak, by the pump method, 

 of 2*8, and was therefore cut down and again purified with 

 ether. It was finally set up in the closed flask connected 

 with the mercury pump on December 13th, 1906. Tested on 

 January 10th, 1907, with an electroscope giving 1*87 to the 

 Y-ray test, it gave a leak of only 0'64, equivalent to l'3x 

 10 _n g. radium. This very satisfactory result is perhaps to 

 be ascribed to the yellow precipitate before mentioned not 

 being worked up and added to the solution in the last puri- 

 fication but added to the residues. An analysis of the solution 

 showed the presence of 481 grams of uranium. It was first 

 pumped out after 56 days on March 7th, 1907, and the gas 

 was introduced and stored in a special electroscope of about 

 50 c.c. volume, constructed out of glass silvered internally. 

 The leaf system has been kept positively charged in the hope 

 that if a solid is deposited, it may follow the usual rule 

 and seek the negatively charged glass rather than the leaf 

 system, which may want renewal in the course of time. The 

 original natural leak of the electroscope was 0*12 in air, and 

 0*11 in a vacuum. The addition of the gas from the uranium 

 increased the leak by 0'13 at first and 0'06 after three days. 

 The last test was done on June 13th, 1907, after the gas had 

 been in the instrument 98 days, and the total leak was then 

 only 0'09, rather less than the natural leak initially. 



The gas was again pumped out from the uranium on 

 June 29th, but it was too large in volume for the second 

 electroscope prepared for it owing to air having leaked in. 

 It is at present being stored in a sealed glass tube while a 

 larger electroscope is being constructed. A test for radium 

 in the solution was done on July 9th, 1907, 208 days from 

 purification, and showed a leak of 0'9 in an electroscope with 

 Y-ray leak of 2*8. 



This is equivalent to 1*23 x 10 -11 gram of radium, which 

 is practically identical with the initial test. The growth of 

 radium in this experiment cannot exceed 5 x 10~ 12 gram. 

 The amount of uranium estimated to have disintegrated is 

 5*3 X 10~ 8 ; so that the production of uranium is here below 

 the ten-thousandth part of the uranium disintegrating. Owing 

 to the much larger amount of uranium and the much smaller 

 initial amount of radium in this experiment than in the last, 

 it constitutes a considerable improvement, and although 



