new Varieties of Vermiculites. 143 



In the next Table we bring together some further noteworthy 

 results, of which the details have already been given, indicating 

 that in the case of three, at least, of the vermiculites we have 

 evidence of different degrees of hydration corresponding to dif- 

 ferent temperatures : — 



IV. VI. II. II. 



Si. £+B. H. 



Atomic ratio of Hallite air-dried .. 2-35 : 2'34 : 176 or 8 : 8 : G 



at 100° . . 2-42 : 2*41 : V47 or 8 : 8 : 5 



at 300° . . 2'48 : 2*45 : 1"25 or 8 : 8 : 4 



Atomic ratio of Pelhamite air-dried 2*45 : 2*19 : 232 or 4 : 4 : 4 

 at 100° . . 275 : 2'46 : 1 '26 or 4 : 4 : 2 

 at 300° . . 2-90 : 2'59 : 74 or 4 : 4 : 1 



Atomic ratio of Jefferisite air-dried 2*30 : 2-28 : 2' 17 or 4 : 4 : 4 

 at 100° . . 2-56 : 2*53 : M7 or 4 : 4 : 2 

 at 300° . . 2-68 : 2"65 : 70 or 4 : 4 : 1 



In the last two varieties the ratios correspond to the symbols 



VIII. VIII. VIII. 



Si 2 8 (R,R).4H 2 

 do. .2H 2 



do. . H 2 0. 



Here again it will be noticed that the differences in the defl- 

 niteness of these ratios correspond to the differences of hygro- 

 scopic power described above. In the case of Hallite, the ratios 

 are almost precisely those of even molecules, while in the case of 

 Jefferisite the agreement is much less close. 



In conclusion, we consider that the following general results 

 may be deduced from this investigation : — 



First. That all the vermiculites are uni silicates. 



Secondly. That these minerals combine with water in several 

 definite proportions, thus confirming the opinion advanced by 

 the writer in his previous paper on this subject, that the water 

 in the vermiculites is water of crystallization. 



Thirdly. That all these minerals may be reduced to the con- 

 dition expressed by the ratio 2:2:1, which we regard as the 

 normal ratio of the vermiculites. 



Fourthly. That the only essential difference between the dif- 

 ferent varieties of vermiculites is in the ratio between the sesqui- 

 oxide and protoxide bases. 



