424 Scientific Intelligence. 
cals which the various varieties contain. The limits usually as- 
signed to this variation correspond to the ratios— 
It VI It VI 
Rom: Si=1:2:3,andR:R:Sisi:1 
the Pargas mica with the ratio 2:3:5 falls between these 
limits ; but the Culsagee variety of vermiculite sores org o the 
more common class of Biotites, which have the ratio ‘2 
But this Sseeecsceeapeh in chemical constitution only a ypears when 
we compare the Biotite mica with the anhydrous Jefferisite; while 
it is the crystallized hydrous Jefferisite which so closely resembles 
and t 
following evidence :— 
As the above analysis shows, the water is united in defi- 
nite and atomic proportions amounting to six molecules to every 
five molecules of silicon in the molecules of the mineral, that is, 
sufficient to convert all the Moon into a hydrate, assuming that 
the five silicon atoms in this oe are joined to each other by 
the smallest possible number of bonds. 
Secondly. While both the rb ctaliberigits and the chemical 
relations of Jefferisite to the other vermiculites, and to the mag- 
nesian micas, eee that the mineral is an melee the 
ic 
Thirdly. Tt was observed by P Prof. ‘Brilt and his observations 
have been fully confirmed by ourselves—that ie water is given 
off at a comparatively low temperature,—about 300° ©. ; and, as 
every mineralogist knows, this dehydration is sttaded with that 
remarkable exfoliation which is characteristic of the vermiculites, 
and indicates a complete disintegration of the molecular structure. 
is exfoliation is wholly different from the phenomena which the 
so-call ydrous micas present under like conditions. these 
last—which, as we suppose, contain hydrogen as a part 0 of the 
basic radical of their molecules—a very high t temperature is Te 
quired to expel the water, and the loss is ee by no such 
marked change of volume and disintegratio 
The conclusion that we draw from these fini: is, that the com- 
bined water is in the same condition in J efferisit ite as in the zeolites, 
know J 
here attempt to discuss what are the relations of the water thus 
combined to ) the = — of the mineral. This ques 
present. t is to. Hee the phenomena presented by the ea 
eo : th e f) 
prominent the two points: Ist. That the ¢ tallographi 
ture of Jefferisi ies identical with that of the magnesian 
