222 Dr. W. A. Tilden. On the Condition in which [Jan. 23, 



cleveite which had been heated to 400° circ. in a vacuum ; B con- 

 tained 9 grams (1/7 c.c.) of the same which had been heated only 

 to 170° in a vacuum; and C contained 7*5 grams (0*9 c.c.) of arti- 

 ficial lead uranate which had been heated to redness in a platinum 

 crucible. The three bulbs, with their contents, were first heated to 

 100°, and at that temperature completely exhausted of air. Gas 

 was then admitted till the apparatus was filled with it at atmo- 

 spheric pressure. The horizontal tube was then sealed off by the 

 blowpipe between the bulbs and the pump, and, by raising the 

 mercury reservoir, a pressure of nearly 7 atmospheres was obtained. 

 The bulbs were heated by a water bath for three days (18 hours), 

 and the pressure was maintained during a total of about 96 hours. 

 Each bulb was then separately cut off, sealed to the Sprengel pump, 

 and exhausted. 



A, heated in an air bath to about 360°, gave 0'25 c.c. of gas rich in 

 helium, but containing a little carbon dioxide. The mineral had 

 absorbed rather more than one-seventh of its volume. 



B, heated in an oil bath, gave 0'44 c.c. gas between 120° and 162°. 

 This also contained much helium, with carbon dioxide. It corre- 

 sponds to more than one-fourth the volume of the mineral. 



C, heated to 150°, gave 0*24 c.c, and a further quantity, 018 c.c. 

 at 150° to 210°. This gas, however, consisted almost wholly of 

 carbon dioxide with a little air, but showed no trace of helium. 



The mineral cleveite, therefore, appears to be capable of re-absorb- 

 ing helium to an extent which increases with the pressure, and which, 

 is, roughly, proportional to the pressure. The pressure under which 

 the original mineral was charged must have been considerable, 

 probably amounting to several hundred atmospheres. 



As hydrogen is readily absorbed by certain metals, especially 

 iron and palladium, it was thought possible that helium would also 

 be readily taken up by the same. A piece of thin sheet-iron was, 

 therefore, carefully polished and heated to low redness in a bulb 

 sealed to the Sprengel pump till all gas had apparently been expelled. 

 The gas extracted from iron gave no indication of the presence of 

 helium. Gas from cleveite, purified from carbon dioxide and dried 

 as before, was admitted till the pressure amounted to about five-sixths 

 of an atmosphere. The iron was heated to redness and cooled in 

 contact with the gas, the excess of gas was then pumped out, and 

 the iron heated by a Bunsen flame. It gave a small quantity of a 

 gas consisting of hydrogen and carbonic oxide and a little helium. 

 Repeating the admission of the gas, heating, &c, the iron gave off 

 a second time about one-third of its volume of gas of the same com- 

 position. The yellow D 3 line was weak in the spectrum of both these 

 products from the iron, although it was very brilliant in the cleveite 

 gas to which the metal had been exposed. It appears, therefore. 



