134 Proceedings of the Royal Society 
and sublimes readily at temperatures far below its fusing point. The 
point of fusion was found to be about 45° C. When exposed to a 
slightly higher temperature it boils with partial decomposition, 
leaving a slight trace of chloride of ammonium. Owing to the 
readiness with which it decomposes, great difficulties were 
experienced in its analysis, and the results have hitherto been 
somewhat discordant. They lead to the formula, C 3 H 10 Cl 2 N 2 O, or 
C 3 H 4 C1 2 0 + 2NH 3 , and it is possible that it may be the represen- 
tative in the acetic series of the hydrochlorate of flavine. 
The author is at present engaged in the further examination of 
this substance and the products of its decomposition. 
4. On Centres, Faisceaux, and Envelopes of Homology. By 
Eev. Hugh Martin, M.A. Communicated by Professor 
Kelland. 
5. On the Effect of Pressure upon Bock Salt and Iceland 
Spar. By M. Beusch, Professor of Natural Philosophy in 
the University of Tubingen. Communicated by Sir David 
Brewster. 
Sir David Brewster, 
& Edinburgh. 
Monsieur, — Les semaines passees j’ai trouve quelques faits dans 
le sel gemme et le spath d’lslande, que je prends la liberte de vous 
communiquer, parceque je m’imagine, qu’il n’y a personne au 
monde, qui saurait mieux apprecier la valeur des petites choses qui 
se sont offertes a moi. 
Dans le sel gemme il y a un clivage ou passage multiple, omis 
it tort par les mineralogistes, qui jouit des proprietes singulieres 
et qui jetera peut etre quelque lumiere sur 
le phenomene, de la “polarisation lamellaire.” 
Ce passage suit les faces du granatoedre ou 
dodecaedre regulier. En pressant un morceau 
carre, dont deux aretes opposees sont enlevees 
par la lime, on obtient par une pression modique 
un passage brillant suivant la diagonale. 
Mais on peut avoir les six passages dodecaedriques tous a la fois en 
