T M E 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



FEBRUARY 1838. 



XXII. On a neix) Property of Nitre. By H.F.Talbot, ^55'., 



i^.2?.S.* 

 5. 1. 'T^HE property of nitre, of which I purpose to commu- 

 -■- nicate a short account, is one which appears to me 

 to have an immediate bearing upon the fundamental doctrines 

 both of double refraction and of crystalline structure in ge- 

 neral ; and I think it requires that some modifications should 

 be made in the received theory on those subjects. 



In general, crystals are formed by successive depositions 

 of layers of particles on a small primitive nucleus. For in- 

 stance, when a hot solution of some salt grows cold, we ob- 

 serve the crystals grow and extend themselves in a manner 

 analogous to vegetation. Or if the crystals have geometrical 

 figures, these appear at first of the smallest size and gradually 

 increase in all their dimensions. 



The crystalline structure may be destroyed by igneous fu- 

 sion. For instance, it is stated that quartz which has been 

 fused is destitute of the double refraction which characterizes 

 it in its natural state. I have not tried this experiment myself, 

 but I believe that it is the received opinion, that the structure 

 not only of this, but of all crystals, is destroyed by fusion, so 

 as oot to be recovered in growing cold. 



Nevertheless the following experiment decisively shows that 

 this opinion is erroneous. 



Put a drop of a solution of nitre on a small plate of glass, 

 and evaporate it to dryness over a spirit-lamp ; then invert 

 the glass, and hold it with the salt downwards and in contact 

 with the flame. By this means the nitre may be brought into 



* Communicated by the Author. 

 Fhil Mag, S. 3. Vol. 12. No. 73. Feb. 1838. U 



