Properties of' the Tzvo New Fluids in Minerals. 129 



remarkable case of this kind happened to a son of Mr Sander- 

 son, who put one of the Quebec crystals of quartz into his 

 mouth. Even with this small accession of heat the specimen 

 burst with great force, and cut his mouth. The fluid which 

 was discharged had a very disagreeable taste. 



In the various cavities described in my former paper, the 

 whole of the expansible fluid, when exposed to healt, was ei- 

 ther driven into vapour,* or retained its fluidity after it had 

 filled the vacuity. Since that paper was published, however, 

 I have discovered cavities in which, after the application of 

 heat, there may be said to be three different substances, viz. 

 1. The expansible fluid in a state of fluidity; 2. The dense 

 fluid; and, 3. The vapour of the expansible fluid. This cu- 

 rious fact will be understood from Fig. 8, which represents a 

 cavity in a specimen belonging to Mr Spaden. The cavity is 

 one-twelfth of an inch long. The expansible fluid is lodged 

 at N N and N' N', where there are large vacuities V, V', and 

 there is a globular portion of it at n, without a vacuity. 

 When heat is applied, the fluid at N N and N' N' quickly 

 goes off into vapour ; the portion at n expands into an ellipti- 

 cal globule, but its force is not sufficient to displace the mass 

 of the second fluid between n and N, and n and N' ; and be- 

 ing kept in equilibrio by the opposite and nearly equal expan- 

 sive forces of the vapour in N N, and N' N', it consequently 

 remains fluid at n. In a plate of topaz shown to me by Mr 

 Sivright, where the expansible fluid consists of two portions 

 floating in a large quantity of the dense fluid, one of the por- 

 tions is a spherical drop which expands with heat, and con- 

 tracts with cold, exhibiting by transmitted light an effect simi- 

 lar to the opening and shutting of the pupil. 



In re-examining the phenomena of the second or denser 

 fluid, several very curious facts have come under my notice. 



I had previously shown, that, when several cavities com- 

 municated with each other, the narrow necks, or lines which 

 joined them, were filled with the dense fluid, which shifted its 



" One of the largest vapour cavities that I have seen is one-twelfth of 

 an inch every way. It is less than half full of fluid, and hence it is 

 driven into vapour by heat. During the precipitation of th« vapour it 

 becomes perfectly opaque. 



VOL. V. NO. I. JULY 1826. 1 



