498 



supernatant liquid perfectly clear. They are then filtered through 

 separate funnels, and washed with hot water. No. 1 is dried and 

 weighed. No. 2 is digested in bromide of potassium, dried and 

 weighed ; and No. 3 in iodide of potassium, dried and weighed. 



To test the method, a mixture was made of 5 grains of iodide of 

 potassium, 5 grains of bromide of potassium, and 5 grains of chlo- 

 ride of sodium. The following is a comparison of the theoretical 

 and experimental results : 



EXPERIMENT. THEORY. 



Iodine 3'69 3-81 



Bromine 3*51 3-34 



Chlorine 2-92 3'02 



I have availed myself of this method in analysing several silver 

 ores containing chloride, bromide and iodide of silver found in Chili, 

 the formulae of which I subjoin : 



Chloride of silver Ag Cl. 



Chlorobromide of silver 2Ag Cl, Ag Br. 



Chlorobromide of silver 3 Ag Cl, 2Ag Br. 



Chlorobromide of silver Ag Cl, 3Ag Br. 



Bromide of .silver Ag Br. 



Iodide of silver Ag I. 



V. "Note on the Density of Ozone." By THOMAS ANDREWS, 

 M.D., F.R.S., Vice-President of Queen's College, Belfast, 

 and P. G. TAIT, M.A., Fellow of St. Peter's College, Cam- 

 bridge, and Professor of Mathematics in Queen's College, 

 Belfast. Received June 17, 1857. 



It is known that Ozone can only be obtained mixed with a large 

 excess of oxygen. In a former communication by one of the authors 

 of this note, it was shown that in the electrolysis of a mixture of 8 

 parts of water and 1 of sulphuric acid, the mean quantity of Ozone 

 does not exceed -0041 gramme in a litre of oxygen, or T y^th part. 

 By using a mixture of equal volumes of acid and water, the relative 

 quantity of Ozone may be doubled ; but even with the Ozone in this 



