320 



Prof. W. Ramsay and Mr. M. W. Travers. 



The Fractional Diffusion of Helium. 



The first sample of helium employed was prepared from samar- 

 skite and cleveite. After seventeen rounds, involving 102 operations, 

 the diffusion rates of the lighter and heavier portions were measured. 

 The first gave a density, calculated from this rate, of 1*807, and the 

 second of 2*128. The same gas was re-diffused until in all thirty 

 rounds had been carried through, involving 180 operations. The 

 light fraction now showed the density (measured diffusion rate 

 against hydrogen) 1*816, and the heavy fraction 2*124. These gases 

 were then circulated ; the diffusion rate of the lighter portion pointed 

 to a density of 1*811 ; the heavier gas was diffused into three por- 

 tions, of which the more rapidly diffusing had a " diffusion density " 

 of 1*906, and the less rapidly diffusing of 2 032. The lightest gas of 

 all (diffusion density = 1*811) was weighed, and had a " real " 

 density (O = 16) of 2 021 ; the mixture of the heavy products gave 

 the real density, 2*153. The refractivity of the heavy portion, 

 measured against helium from cleveite, undiffused, yet purified from 

 all removable gases, which had the density (weighed) 2*076, was 

 1*078, the refractivity of the undiffused gas being taken as unity. 



A fresh quantity of helium was next prepared from cleveite, and 

 the former diffused samples were stored in tube-reservoirs for future 

 use. The new helium was washed with caustic soda, but not other- 

 wise purified. This gas was now put through fifteen rounds, com- 

 prising ninety operations, and the light portion in jar 6 was purified 

 by circulation over magnesium and copper oxide. Its refractivity 

 was 0*9752 of that of the uncirculated helium. Its density by 

 weighing was 1*979. Owing to the cracking of the glass apparatus 

 the main bulk of the specimen was lost. It may be here interesting 

 to chronicle that the remaining portion was inhaled through the nose 

 and mouth ; it possessed neither smell nor taste. 



The contents of No. 5 were therefore purified and weighed; its 

 density was 2 049. 



The contents of No. 1 were also purified by circulation, and had a 

 gravimetric density of 2*245. It lost on circulation a considerable 

 amount of nitrogen which was estimated as ammonia by treat- 

 ment of the magnesium containing nitride with water. As we are 

 certain that there was no entry of air in preparing the gas, the 34 c.c. 

 of nitrogen must have been evolved from the mineral. It may have 

 been occluded on the surface of the powdered mineral ; it need not 

 be remarked that before heating the mineral a nearly perfect vacuum 

 was made in the tube, and that there was no leakage during the 

 operations. We have previously found traces of nitrogen in gas 

 prepared from cleveite ; but not all specimens give off' that gas. 

 Supposing, however, to take the worst view, the nitrogen had been 



