SCIENTIFIC SUMMARY. 
317 
through the solution on the addition of a nucleus, causing a deposition of 
the body belonging to the nucleus only ; (2) That when sudden crystalliza- 
tion takes place, causing the deposition of both salts, there is a preponderance 
of the salt of the same nature as the nucleus ; (3) That the nucleus may 
remain growing slowly in the solution, becoming increased by a deposition 
of the salt of the same nature as the nucleus. And (B) When the mixture 
consists of two isomorphous salts : (1) Sudden crystallization may occur 
giving a deposition of both salts, apparently in the proportion in which they 
exist in solution ; (2) That when slow crystallization takes place, the nucleus 
increases by a deposition of the least soluble salt, showing that in mixed 
supersaturated solutions a gradation of phenomena may be experienced, 
passing from those shown in the crystallization of a true supersaturated 
solution to those shown in the crystallization of an ordinary saturated 
solution. 
New Compounds of Ammonia and Hydrogen Chloride. — Hydrochloric acid 
and ammonia have hitherto been known only in one form of combination, 
that of sal-ammoniac, analogous to salt and potassium chloride. Troost, 
during his experiments on the vapour density of ammonia compounds, has 
found a number of curious compounds which dry ammonia forms with hydro 
gen chloride, sulphuretted hydrogen, and a number of other mineral and organic 
acids. In a recent communication to the Paris Academy of Sciences ( Compt. 
rend, lxxxviii. 578) he describes two new compounds of ammonia and hydro- 
chloric acid. The first contains four equivalents of ammonia and one of the 
acid ; it melts at + 7°, its crystals energetically depolarize light, and therefore 
do not belong to the same crystalline system as salammoniac; it is anhydrous 
and has the formula HOI, 4NH 3 . The second compound contains seven 
equivalents of ammonia and one equivalent of the acid. It melts at — 18° ; 
the liquid exhibits all the characters of supersaturation ; if rapidly cooled 
it becomes viscous ; and at —40° becomes a transparent solid mass. It has 
the composition HOI, 7NH 3 . 
GEOLOGY AND PALAEONTOLOGY. 
Carboniferous Fenestellidce. — Mr. G. W. Shrubsole has communicated to 
the Geological Society (February 21, 1879), the results of his investigations 
on the British Carboniferous Fenestellidse. He finds that owing to neglect 
on the part of describers to allow for differences in the structure at various 
stages of growth and in different parts of the polyzoarium a great number 
of unnecessary species have been made ; out the twenty-four recorded species 
of Fenestellce he has examined nineteen, and his investigations lead him to 
reduce these to five. 
Tertiary Fossils of Chili. — Descriptions of tertiary fossils from Chili have 
been given by various authors, especially D’Orbigny, G. B. Sowerby (in 
Darwin’s “ Geological Observations,”) and Claude Gay. Dr. B. A. Philippi 
now publishes (Zeitschr. fur die gesammten Naturwiss., 1878), a notice of the 
forms contained in the Museum at Santiago, preliminary to a more detailed 
memoir, which will contain the descriptions of numerous new species. From 
the tertiary deposits of Chili and the dependent islands, he records a great 
