OP ARTS AND SCIENCES. 13 



ing to dull redness. Alkalimetry indicated that 0.32 milligramme 

 should be added to the last weight as a correction for the bromine 

 lost; hence the corrected loss was 0.00018 gramme, or 0.006 per 

 cent. A third trial gave the corrected loss of 3.5 grammes of 

 baric bromide between 185" and a dull red heat as 0.00027 gramme, 

 or 0.008 per cent. Again, 3.4 grammes of a less pure specimen of 

 the salt lost 1.2 milligrammes between 200° and dull redness, of 

 which loss eight tenths of a milligramme was accounted for by the 

 baric carbonate found in the dissolved residue. In Experiment 19, 

 about 3.5 grammes of the salt dried at 260° lost 0.04 milligramme 

 on heating to 340°, and 0.27 milligramme more upon subjection 

 to a red heat. In order to prove that the method of desiccation 

 over sulphuric acid was sufficient for the purpose in hand, this 

 specimen was again heated to 400°, and cooled in a vacuum over 

 phosphoric oxide. After the admission of dry air the crucible and 

 contents were found to have gained a little less than a twentieth of 

 a milligramme. Since seventeen one-hundredths of a milligramme 

 must be added to the last weight of the salt to correct for the 

 amount of alkali found, it is evident that the salt dried at 340° in 

 the first place could not have retained more than 0.005 per cent of 

 water, which could be expelled at a red heat. 



The most severe test of the hygroscopic constancy of baric 

 bromide was obtained by fusion. 17.4841 grammes of baric bro- 

 mide which had been thoroughly dried at a dull red heat were fused 

 in a platinum crucible, and were found to have lost 4.1 milli- 

 grammes during the process. 2.25 cubic centimetres of twentieth 

 normal hydrobromic acid were required to render the solution of 

 the clear cake neutral to phenol phthalein, and 0.10 cubic centi- 

 metre more made it strongly acid to methyl orange. These 

 figures involve a correction of 7.0 milligrammes to the second 

 weight of baric bromide, making it 17.4870 grammes. The ex- 

 cess of this weight over the first (17.4841) is completely accounted 

 for by the knowledge that a slight indeterminable correction* 

 should have been applied to the earlier one, owing to its previous 

 loss of bromine. The crucible was found to have lost 0.20 milli- 

 gramme. 



Again, two grammes and a half of baric bromide heated to con- 

 stant weight at 185° lost 2.11 milligrammes on being fused in a 

 double crucible. Of this weight all but 0.17 milligramme (0.007 



* From 0.010 to 0.03 per cent. 



