136 M. Wohler 011 the Composition of the 



In concluding these observations, I could have wished to 

 enter into some details respecting their geological relations ; 

 but as these would lead us too far into the regions of specula- 

 tion, I shall not enter upon them on the present occasion. It 

 may be proper, however, to state, that the opinion which I 

 hazarded in a former paper, that the discovery of the two 

 new fluids in minerals attached a new difficulty to the aque- 

 ous hypothesis, has been rendered more probable by every 

 subsequent inquiry ; and that I can see no way of account- 

 ing for the phenomena, but by supposing that the cavities 

 Mere formed by highly elastic substances, when the mineral 

 itself had been either in a state of fusion, or rendered soft 

 by heat. 



Art. XXIX. — On the Composition of the Native Phosphates 

 and Arseniates of Lead. By F. Wohler.* 



jYlaproth has given the analysis of four specimens of lead- 

 spar, in the third volume of his Contributions, the composi- 

 tion of which is as follows : 



Barytes, with fluid cavities of the same general character with those 

 which I described in my former paper, but much larger than any 

 which I had seen. Upon grinding down, on a dry stone, one of the 

 faces of this specimen, the largest cavity burst, and discharged its fluid 

 contents through the fissure upon the ground surface of the specimen. 

 The fluid lay in drops of different sizes along the line of the fissure, and, 

 in this condition, Mr Nicol put it into his cabinet. Upon looking at the 

 specimen about twenty-four hours afterwards, each drop of fluid had be- 

 come a crystal of sulphate of barytes. These crystals had the primitive 

 form of the mineral. 



This very curious fact is analogous to the uncrystallized water in the 

 ice-cavities mentioned above, the crystallization in both cases being pre- 

 vented by pressure. When that pressure was removed, a portion of the 

 water and the fluid sulphate of barytes were immediately crystallized. 

 Mr Nicol distinctly remarked, that the crystals occupied nearly as much 

 space as the drops of the fluid ; so that the crystals of sulphate of barytes 

 were not deposited from an aqueous solution, but bore the same relation to 

 the fluid from which they were formed, as Ice does to Water. 



" Abstract from Poggendorf's Annalen dcr Physik und Chemic, vol. iv. 



