6 Mr. Levy on the Identity 



and then increases again. The general form of the expression 

 has likewise been assigned ; and it will readily appear that 

 the quotient is represented by the square of the ordinate to 

 the conjugate axis of a hyperbola, the square of the semitrans- 

 verse axis being the minimum. To show this we need only 

 put the expression (B) in this form, viz. 



!!!_i2: = A + B (« - 1)\ 



A and B being known numbers, and n the distance of the 

 minimum from the boiling point. But it is sufficient to have 

 mentioned these things, the length of this paper warning me 

 that it is time to stop writing. 

 Nov. 5, 1826. J. Ivory. 



II. On the Identity ofEpistilbite a?id Heulandite. By A. Levy, 

 Esq. M.A. F.G.S* 



"rjR. GUSTAVUS ROSE, of Berlin, in the eighth num- 

 -■-^ ber of the Edinburgh Journal of Science, has given the 

 description of a mineral species which he has considered as 

 new, and named Epistilbite. He states that the most consi- 

 derable differences between this species and Heulandite are 

 those in their regular forms, the physical characters and che- 

 mical compositions of both species being nearly exactly the 

 samef. When I read his paper it struck me, however, that 

 the forms and angles of Elpistiibite might be derived by simple 

 and frequently occurring deci'ements from the primitive form 

 I had adopted for Heulandite, and that the easy, nacreous, and 

 only cleavage of Epistilbite was parallel to the same modifi- 

 cation of this primitive form, as is the easy, nacreous, and only 

 cleavage of Heulandite It appears to me, therefore, that if 

 this mode of viewing the crystals of the newly described sub- 

 stance should be found correct, there is no sufficient ground 

 to consider it as forming a distinct species from Heulandite ; 

 since the formsof these two substances, which had been thought 

 to constitute their principal difference, may easily be made to 

 agree. 



* Communicated by the Autlior. 



+ Heulandite. Epistilbite. 



Specific gravity 2-211 2-249 



Hardness A little greater than Heulandite. 



Blowpipe The same indications as in Heulandite. 



f Silica . . . 59-95 58-59 



I Alumina . . 16 87 17-52 



Analysis i. Lime .... 7" 19 7-56 



I Water . . . 1510 14-48 



I^Soda 1-78 



Fig. 



