ANNIVERSARY ADDRESS OF THE PRESIDENT. CXV 
slags were square prisms, some having their angles truncated by planes, 
making equal angles with the adjacent faces of the prism. In hardness 
they varied from 5:5 to 6. 
Another slag from a hot-blast furnace at Oldbury is crystallized 
in thin square plates, the lateral faces of which are perpendicular to 
each other and to the terminal faces. Analyses lead to the formula 
3(3CaO, Si0*) + 3 Al? 0%, SiO*, one which appears also to represent 
the constitution of gehlenite. It is remarked, that admitting this 
slag to be the same with gehlenite, its production at a high tempera- 
ture in an iron furnace is interesting when compared with the mode 
of occurrence of the natural mineral in the Fassathal, Tyrol, a de- 
scription of which by Von Buch is appended. The analyses of 
another slag gave a formula nearly representing that of humboldtite, 
as deduced from the analysis of Von Kobell; at the same time it is 
observed that Damour gives another formula for humboldtite, which 
he believes to be identical with mellilite, and this formula is precisely 
that given for the first series of blast-furnace slags. Another beauti- 
fully crystallized slag was found in form and constitution to resemble 
olivine, the magnesia of the latter being replaced by protoxide of iron. 
A large series of slags from various metallurgical works have still to be 
investigated, and it is hoped that Dr. Percy and Professor Miller may 
ere long still further add to our knowledge of this class of substances, 
so important in their bearing on the minerals found in connection 
with igneous rocks. 
All modes by which we can artificially imitate the minerals found 
in nature are valuable, and more especially if any of these mimerals 
should be what is commonly termed infusible. We have to record 
very important and successful experiments of this kind by M. Ebel- 
men, who has employed a method entirely new. He observes that 
two modes have hitherto been adopted to produce definite and cry- 
stallized combinations. One consists in submitting to igneous fusion 
either simple or compound bodies, alone or mixed with each other 
in certain proportions proper to form the definite combinations, 
whence it often happens that crystals form and become isolated in 
the midst of the melted mass as it cools, thus presenting a substance of 
a porphyritic character. The second method is by sublimation. 
_ M. Ebelmen proceeds upon another and very simple principle. 
He seeks for a substance which at a high temperature acts like water, 
as regards the substances dissolved, either at its ordinary or at a slightly 
elevated temperature. As by the evaporation of water crystallized 
combinations may be obtained, so by employing bodies capable of 
volatilization at very high temperatures, yet at a given degree of heat, 
while in fusion, capable of dissolving the greater part of metallic 
oxides, it was expected that certain calculated proportions of some 
oxides would crystallize, when the dissolving body was evaporated, 
at a great heat, in open vessels. Complete success has attended this 
view. 
In this manner he has produced many minerals. He first men- 
tions those composed of 1 equivalent of oxide consisting of 2 atoms of 
metal and 3 of oxygen, with 1 equivalent of oxide consisting of 1 
h2 
