RICHARDS. — ATOMIC WEIGHT OP BARIUM. 57 



ous determinations in the present research as to serve for the basis of 

 reduction to vacuum. 



4.8620 grams (in air) of baric chloride which had been dried to 

 constant weight at 220° were found to occupy the same volume at 24° 

 as 1.2608 grams of water reduced to 4°. Hence the specific gravity of 

 baric chloride under these conditions is 3.856, a value which agrees 

 essentially with those given above. 



Here, as in the case of baric bromide, the question whether the water 

 of crystallization is absolutely expelled at a red heat is one of the 

 greatest importance. All early experiments have assumed that this is 

 the case, without attempting to disprove the contrary assumption. 

 The first stumbling block in the way of the careful investigation of the 

 problem is the decomposition of baric chloride in the air at high tem- 

 peratures. Marignac's statement that the salt may be ignited at a dull 

 red heat without the loss of a trace of chlorine * has not been con- 

 firmed by the present experience. As a matter of fact, baric chloride 

 loses almost as much halogen as the bromide, upon gentle ignition in 

 the air.f Hence in order to determine the true weight of baric chlo- 

 ride present in all those cases where the salt was ignited in this way, it 

 was necessary to determine the amount of baric hydroxide and baric 

 carbonate existing in the solution of the ignited salt. Pure boiled 

 water which had been prepared solely in platinum was used for mak- 

 ing this solution, and phenol phthalein and methyl orange were used 

 as indicators. Of course, the loss of 0.00355 gram of chlorine would 

 correspond to a correction of -f 0.00055 gram to the weight of the 

 baric chloride if the alkaline earth were in the form of carbonate, 

 +0.00185 gram if it were in the form of hydroxide, or +0.00275 gram if 

 it were in the form of oxide. Since it is somewhat uncertain whether 

 the portion which is determined by phenol phthalein really exists 

 when dry in the form of hydroxide, and not in the form of oxide, the 

 mean of the last two figures, 0.0023 gram, was adopted in the work which 

 follows. In the case of baric bromide, this correction was calculated 

 for the hydroxide. The corrections are in any case so very small that 

 the possible error introduced by either method of procedure is quite 

 unimportant. Another possible error of about the same magnitude is 

 to be found in the fact that pure baric carbonate is not wholly without 

 influence upon phenol phthalein. 



In order to observe the behavior of baric chloride under gradually 



* Liebig's Annalen, LXVIII. 215; CVI. 165. 

 t Schultze, Journ. f. prakt. Chem., [2], XXI. 407. 



