372 Mr. C. Schorlemmer on the Derivatives of Propane. [Apr. 8, 



sibly is tridymite. In bulk it forms about a third part of the mixed 

 crystalline mass. 



The crystals are very imperfect, and are twinned : but there are two 

 cleavages parallel to the planes of a prism of about 119° ; and, on looking 

 through a plane that is perpendicular to this zone, it is seen that the 

 crystal is biaxial. The normal to this plane is parallel to the second mean 

 line, the optical character being negative. 



A section made for examination in the microscope showed two small 

 crystals in which light traverses the section with equal brilliancy during 

 its rotation between crossed Nicol prisms. This, and possibly a similar 

 case recorded by Vom Rath, seems to result from the section being cut 

 parallel to a composite portion of the crystal. 



The analysis of the mineral gave, by distillation of the silica as silicic 

 difluoride, and subsequent determination as potassic fluosilicate, 97*43 per 

 cent, of silica, the remainder being oxide of iron and lime. Thus 0*3114 

 grm. gave : 



A second analysis gave 99*21 per cent, silica, 0*79 of residue. 



Its specific gravity, as determined from a very small amount of the mi- 

 neral picked under the microscope, was 2*18 ; a second determination 

 made on a larger amount gave the value 2*245. That of tridymite is 

 2-295 to 2*3. This may be taken as evidence that the mineral is not 

 quartz, the specific gravity of which is 2*65. Vom Rath's experiments 

 were made on a rather less pure form of tridymite. 



There can be no doubt from these results, further details of which shall 

 be shortly laid before the Society, that this mineral is silica in the form of 

 its allotropic condition and lower density. It may possibly be the mineral 

 to which Vom Rath has given the name of Tridymite ; the crystalline 

 system, however, of Tridymite, as given by Vom Rath, does not accord with 

 the above facts. 



II. "On the Derivatives of Propane (Hydride of Propyl)." By C. 

 Schorlemmer. Communicated by Prof. Stokes, Sec. R.S 

 Received March 5, 1869. 



At the time when I commenced this investigation, the existence of 

 normal propyl alcohol was very doubtful. According to Chancel*, this 

 body is found in the fusel-oil from the marc of grapes ; but Mendelegefff 

 tried in vain to isolate it from a sample of this oil which he had obtained 



* Compt Rend. vol. xxxvii. p. 410. t Zeitschrift fur Chemie. 1868, p. 25. 



Silica .... 

 Ferric oxide 

 Lime .... 



0*3034 

 0*0035 

 0*0018 

 0*3087 



per cent. 



97*43 

 1-124 

 0-578 



99-132 



