1865.] of the Brochantite Group. 395 



air, the liberated water being retained by sulphuric acid iu pumice in a 

 bulbed TJ-tube. In the other cases the mineral was heated with oxide of 

 lead, and the water estimated by the loss. 



From the slight differences in the numbers given by the sulphuric- acid 

 determinations in these minerals, and from the difficulty of determining the 

 values of traces of iron, lime, and impurities as disturbing elements in the 

 calculation of the analysis, the water-determinations are especially impor- 

 tant. The following are the numbers the analyses have yielded me 1st, 

 crystals of Langite, carefully selected ; and 2nd, of the much paler blue 

 incrustation or aggregation of crystalline Langite, generally showing the 

 plane 1 largely developed on the surfaces of the incrustation : 



Copper-Determination. 

 I. Picked crystals. 

 Grammes. Per cent. 



i. 0-2024 gave 0'1074 copper, corresponding to 53'06 



ii. 0-2185 took 18'18 cub. centims. of standard solution of hypo- 

 sulphite of soda, corresponding to* .... 52-26 



iii. 01866 15'2 52-10 



II. Pale Blue Langite. 

 iii. 0-4295 35-8 ' 52-80 



Average =52'55 

 Sulphuric Acid-Determination. 



I. Picked crystals. 



0-2746 gave 0-1297 Ba SO 4 , corresponding to -04457 SO 3 . . =16-20 



1-6687 0-80475 Ba SO 4 , corresponding to -27587 SO 3 . . =16'23 



0-288 0-1375 Ba SO 4 , corresponding to -0470085 SO 3 . . =16'35 



II. Pale Blue Langite. 



0-1701 0-0826 BaSO 4 , corresponding to -028387 SO 3 . . =16-61 

 0-4295 0-2094 Ba S0 4 , corresponding to '07196 SO 3 . . = 16-75 



Average =16-42 

 Water-Determination. 



I. Picked crystals. 



i. 0-3622 lost . . . 0-0649 Water, corresponding to .... 17'93 



[ii. 0-4737 ... 0-0915 , 19-31] f 



iii. 0-7210 with oxide of lead 0'1326 . .... 18'39 



II. Pale Blue Langite 



iv. 0-2258 0-0423 . .... 18-73 



Omitting the 2nd, the average=18'3l7 



There are traces of lime and iron ; of the latter I found in one experi- 

 ment 0'03 per cent. 



* Two preliminary experiments with the standard solution on pure crystallized sul- 

 phate of copper and one on pure copper gave 



99-66 per cent. ] 



99-965 \ of the copper required by calculation. 



99-92 J 



t A little acid came over in this experiment. 



