Prof. J. P. Cooke on the Vermicidites. 263 



This close agreement indicates that all the water lost in drying, 

 either at 100° or over sulphuric acid, is hygroscopic ; and the 

 conclusion is very strongly confirmed by the fact that the mineral 

 in thus drying does not change its aspect in the least degree, 

 and rapidly reabsorbs the water when exposed to the air. On 

 the other hand, when the mineral is ignited it swells up to many 

 times its volume, like other members of the vermiculite family, 

 and undergoes what is evidently a profound alteration in its mo- 

 lecular structure. 



a) 



Si. 



r 37-58 



20-04 



20-04 



[. 203 



r 37-43 

 19-96 



19-96 

 u 2-03 

 .37-10 



19-79 



Al. Fe. 



19-73 5-95 

 9-19 1-78 



Fe. Mg. 

 0-58 25-13 

 0-14 10-05 



v * J 



10-19 

 103 



0-58 25-58 



0-14 10-23 



v. j 



H. 



1109 = 



9-86 



9-86 



1 



11-09 = 



9-86 



9-86 

 1 

 11-09 = 



9-86 



9-86 

 1 



= 10006 



10 : 97 

 111 



19-75 5-95 

 9-20 1-78 



1-11 



20-22 5-95 



9-42 1-78 



= 100-38 



10-37 

 105 



0-58 25-07 

 0-14 1003 



1017 

 1-03 



= 10001 



19-79 

 - 2 



11-20 

 1-13 





(2) 



(3) 



It is evident from these analyses that the atomic ratio of the 

 mineral is 2 : 1 : 1 : 1 ; and its formula may therefore be written 



R 3 ,R.0 12 .Si 3 .3H 2 0. 



By referring to what has already been said of the relation of 

 Jefferisite to the Biotites, it will be seen that while that mineral 

 corresponds to a less common variety of this species, the Cul- 

 sagee vermiculite corresponds to its more usual type. We give 

 below at (1) the results of an analysis of Vesuvian Biotite by 

 Chodnef, and at (2) the same, assuming that a portion of the 

 iron is in the ferrous condition, as is well known to be the case, 

 in order to show that values within the probable error of the 

 analysis would give the ratio 2:1:1. Here, of course, the 

 alkali takes the place of a portion of the magnesia of the ver- 

 miculite. 



