56 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The following atomic weights of various elements entering into the 

 present research will be assumed throughout the paper: — 



Oxygen =16.000 Hydrogen = 1.0075 



Bromine = 79.955 Silver = 107.930 



Chlorine = 35.456 Sulphur = 32.065 



Properties of Baric Chloride. 



The properties of baric chloride are so familiar as to need little 

 further description.* The colorless flat tables of the rhombic system 

 contain, as is very well known, two molecules of water together with 

 the usual slight excess. Half of this water is given off at 60-65°, f 

 and the rest at somewhat higher temperatures. All the water is re- 

 gained at ordinary temperatures in ordinary moist air. According 

 to Filholf the crystals possess a specific gravity of 2.66, while 

 according to Joule and Playfair,|| Schiff,§ and Schroeder If they pos- 

 sess a specific gravity of about 3.05. This great discrepancy is too 

 serious to neglect, hence a redetermination was made. 



The apparatus for the determination of the specific gravity was simi- 

 lar to that already described,** and toluol was again used as the liquid 

 to be displaced. 5.701 grams (in air) of powdered crystallized baric 

 chloride were found to displace 1.5864 grams of toluol at 24°, or 1.8408 

 grams of water at 4°. Hence the specific gravity sought is 3.097. 

 The reason for at least a part of the discrepancy is undoubtedly to be 

 found in the enclosure of varying amounts of mother liquor iu the 

 crystals. 



The specific gravity of anhydrous baric chloride has been much 

 more definitely determined. According to Quincke,ft the value of this 

 constant is 3.851 at 0°; according to Favre and Volson,$$ it is 3.844 

 at 17°; and according to Schroeder,§§ it is 3.879 at 4°. Although 

 without doubt the mean of these values would have served the present 

 purpose, a new determination was made, as much to check the previ- 



* See Graham Otto (Micliaelis), III. 658; also Watt's Dictionary (Muir), 

 I. 441, etc. 



t Lescceur, Compt. Rend., CIV. 1511. 



| Graham Otto (Michael is), loc. cit. 



|| Chem. Soc. Mem., II. 401 ; III. 57, 199. 



§ Annalen,CVIII. 21. 

 "IT Jahresbericht 1879, p. 31. 

 ** These Proceedings, XXVIII. 14. 



tt Graham Otto (Micliaelis), III. 659. # Ibid. 



§§ Berichte d. deutsch. c. Gesell. 1878, 2131. 



