1880.] NATURAL SCIENCES OF PHILADELPHIA. .325 



bubbles went off slowly, but there was no exfoliation. The tem- 

 perature being raised, it made tlie first movement at 160°, exfoli- 

 ated vigorously at 175°, and at 180° rose from its support to the 

 surface of the parafline. 



(d) Another piece similarly immersed gave bubbles briskly at 

 1.30°, and began to exfoliate at 160°. 



(e) Pieces thrown into melt'ed parafline whose temperature had 

 previously been raised to 1G0° C, immediatel}^ exfoliated and rose 

 to the surface. 



(/) A large piece did not exfoliate even after the temperature 

 had been gradually raised to 225° C. 



(g) Immersed in melted sulphur, it immediately exfoliated and 

 strongly effervesced. 



(h) Immersed in concentrated sulphuric acid which had been 

 heated to 160° C, it immediately exfoliated and became pure 

 white, being completeh- and immediately^ decomposed. Immersed 

 similarh' at a temperature of 150° C. it exfoliated, but did not 

 become immediatel}^ white. At a lower temperature no exfoliation 

 occurred. A similar piece being similarly immersed and the tem- 

 perature raised, began to exfoliate at 130° C, and continued ex- 

 foliating as the temperature rose, though being meanwhile decom- 

 posed. This sudden change of form and color upon immersion in 

 hot sulphuric acid recalls a somewhat similar change in the efflor- 

 escence of protosulphate of iron when immersed in the same acid. 



It is seen from these experiments that no absolute determination 

 of the exfoliation temperature is possible. By a verj- slow heat a 

 large proportion of the water (about 5 per cent.) can be driven off' 

 and the mica raised to a high heat without any exfoliation of 

 consequence. The following experiment illustrates this fact. 



(/.) A piece of Philadelphite was cut into two equal portions. 

 One piece, heated suddenly on platinum foil to a red heat, exfoliated 

 to ten times its original volume. The other piece was slowly 

 heated in an air-bath. At 285° C. it had exfoliated but very 

 slightl\'. It was then taken out and heated on platinum foil to a 

 red heat, when it exfoliated very little more, becoming only one- 

 fourth the length of the first piece. 



A similar experiment has been made upon heulandite and stilbite 

 from near Philadelphia. Both of these zeolites, as is well known, 

 exfoliate largely when held in the flame. It has been found that 

 if the}' are heated very slowlj- on platinum foil, they can be raised 



