RICHARDS. — ATOMIC WEIGHT OF STRONTIUM. 377 



twice distilled in platinum, and the nitrate was crystallized twice suc- 

 cessively in a platinum dish. Each quantity of crystals was washed 

 with small quantities of water and tliree or four additions of alcohol. 

 The first mother liiiuor, upon being fractionally precipitated by means 

 of alcohol, showed distinct traces of calcium in the extreme solution ; 

 thus Barthe and Falieres's method was not capable of freeing the 

 substance wholly from calcium. The second mother liquor showed 

 no trace of calcium upou the most careful scrutiny. 



Two hundred grams of the purest crystals, after having been dried 

 at 130°, were dissolved in about a litre of the purest water and filtered 

 into a large platinum dish, into which was passed first pure ammonia 

 gas and then pure carbon dioxide through a platinum tube.* The 

 pure strontic carbonate was washed by decantatiou eight or ten times, 

 dried on the steam bath, and ignited in a double platinum crucible 

 over a spirit lamp. 



Part of this carbonate was converted into bromide by means of the 

 purest hydrobromic acid,t and the product was digested for a long 

 time with a considerable excess of carbonate. After filtration and 

 evaporation the strontic bromide was fused in a platinum dish over 

 the spirit lamp, the salt being perfectly clear while liquid. The trans- 

 lucent cake was dissolved, allowed to stand, filtered, faintly acidified 

 with hydrobromic acid, and crystallized twice from water. Each time 

 the crystals were washed with the purest alcohol. The resulting bro- 

 mide of strontium was used for Analyses 1, 2, 3, 5, 6, 7, 12, 15, 16, 

 17, and 18. 



The next sample was prepared from the strontic carbonate which 

 had been digested with the strontic bromide just described. It was 

 dissolved in the purest hydrobromic acid and purified much as before, 

 except that the salt was fused twice with intermediate crystalliza- 

 tions, instead of only once. This fourth preparation was used for 

 Analysis 9. 



The fifth sample was made by the repeated crystallization of the 

 combined mother liquors obtained from the four previous preparations. 

 It was used for Analyses 4, 8, and 19. 



The sixth preparation of strontic bromide was made from the stron- 

 tic sulphate remaining from the third. This residue was treated with 

 enough ammonic carbonate to convert all but about twenty grams of 



* See page 379. 



t Prepared from pure baric bromide and redistilled many times. See these 

 Proceedings, XXVIII. 17. 



