320 Mr. J. W. Mallet on Breivsterite. 



fccfc decomposition, and consequent purity of the silicic acid 

 weighed ; the other specimens were treated directly with hydro- 

 chloric acid, which seems of itself to he capable of effecting com- 

 plete decomposition. The baryta was precipitated by hydro- 

 Huosilicic acid* ; and the relative amounts of lime and strontia 

 were determined indirectly, by weighing the mixed earths first as 

 sulphates and then as carbonates. 



The following are the results obtained : — 



I. II. III. IV. V. Mean. Atoms. 



Silica 54-49 53-66 54-.-?l 54-84 ... 54-42 1-209 4-08 



Alumina 15-42 15-29 15-05 1525 -296 1 



Peroxide of iron trace -08 trace 



Baryta 6-76 6-84 6-80 -0891 



Strontia 8-79 9-20 8-99 -173^304 103 



Lime -92 1-46 119 -012] 



Water 1339 1306 13-22 1-469 496 



99-67 99-87 



Analysis IV. was spoiled by an accident ; and in III. the de- 

 termination of the earths was abandoned on ascertaining the ne- 

 cessity for the removal of ammoniacal salts before precipitating 

 baryta {vide note), a precaution which had not been taken in this 

 case. 



The silicic acid, alumina, protoxides, and water are clearly 

 present in the ratio 4:1:1:5, giving the formula 



(BaO, SrO, CaO), SiO^ + APO^, 3Si03 + 5HO. 



The atomic relation between the lime, baryta, and strontia is near 

 1:3:4. 



* In examining the precautions incident to this mode of determining 

 baryta in the presence of strontia or lime, I have found no notice taken in 

 any work on c-liemical analysis of the solvent effect of ammoniacal salts 

 upon silico-fluoride of barium. 



Fresenius states that the latter dissolves in 3400 to 3800 parts of water, 

 and in 640 to 733 parts of water acidified by hydrochloric acid, but does 

 not mention salts of ammonia. 



I digested i)ure silico-fluoride of barium in the cold, with frequent stir- 

 ring, for fort}-eight hours (a) with a saturated solution of chloride of am- 

 monium, {b) with the same solution diluted with twice its volume of water. 

 The fluid was in each case filtered off" perfectly clear, 100 cubic centimetres 

 were measured, and the baryta was determined as sulphate. 



(a) gave "1942 grm. of BaO, SO'=-2338 grm. of BaF, SiF^. Hence 1 

 part of the latter salt dissolves in 428 parts of a saturated solution of sal- 

 ammoniac. 



(h) gave -1409 grm. of BaO, SO^=-1697 grm. of BaF, SiF=, or 1 part in 

 689 of the diluted solution. 



The necessity of removing ammoniacal salts from a fluid in which baryta 

 is to be determined as silico-fluoride is sufficiently obvious. 



