294 CELESTINE AND BARYTO-CELESTINE OF CLIFTON. 



appearance I supposed them to be nearly pure celestine, and the 

 workmen told me on enquiry that they had been found in round 

 lumps at the bottom of the red marl lying immediately beneath 

 the soil. There seemed to be about two or three tons of this 

 substance and it had been partly used to pave the road. I searched 

 the heaps for blue celestine but could find none, and as I thought 

 it might probably occur in other parts of that neighbourhood, I 

 went to another place about hfty yards north of the east mouth of the 

 railway tunnel, where the stones from the foundations of several 

 houses had been thrown. Here I found what I thought was blue 

 celestine. I proceeded the next day to examine it by means of 

 the flame test, and was surprised to find that it gave after the red 

 of strontium a very decided green llame, which led me to suspect 

 the presence of barium ; in any case this proved that it was not 

 pure celestine. On making a more exact qualitative analysis 

 I soon satisfied myself that barium v/as present in considerable 

 quantity, but failed to detect calcium, or any other substance but 

 strontium and sulphuric acid. The mineral obviously consisted of 

 a double sulphate of barium and strontium, and a mineral of that 

 kind has been found by Thomson, and was called by him haryto- 

 celesti7ie, just as the double carbonate of barium and calcium has 

 been called haryto-calcite, and the double carbonate of lead and 

 calcium, plumho-calcite. Baryto-celestine so far as I can ascertain 

 has not, however, been previously found in the British Isles. 



The quantitative analysis of the mineral seemed to me to be of 

 especial interest to determine whether the two sulphates were 

 present in such proportions as would enable the composition of 

 the mineral to be expressed by a simple formula, or whether it 

 consisted merely of a mixture in indefinite proportions of its two 

 constituents. 



The two sulphates are isomorphous, and isomorphous bodies as 

 is well known can crystallize together in any proportion. On 

 the other hand definite compounds of isomorphous bodies 

 certainly occur in nature, for instance dolomite CaCOs, MgCOs, 



