182%] Philosophical-Y'ransactions for 1822, Part II. 468 
mable substances, the one much more volatile than the other, 
but both inseparable from the stone, except at a heat approachi- 
ing, if not entirely amounting to, whiteness. I imagine that it is 
in combination with the iron, as it seemed in general to accom- 
pany the solutions of that substance, and to modify the colour 
and magnetic properties of the metal..... If it should be found 
to be anew substance, I propose to callit mewrine. I should not 
be surprised, however, Judging from the smell, and its being 
separable from water by evaporation, if it were found to contain 
nicotine in combination with naptha.” 
Result of the analysis of the pitchstone of Newry : 
ilbena SRG aside deus Yow ewiely ss.) 722800 
Ashuisine tei Sette toes a sie. OT ie BEL 1-500 
Hrneen v2 riivelor sees. ake 31120 
Protoxide of iron.’..........ee-265 3°036 
Dddlal. ai atsrteiwites Qos See ses aos stat h QSa7 
Water and bitumen ......++222-2. 8°500 
99-813 
~ The mass which remained in the retorts after the distillation of 
this mineral was pumice, having the colour, levity, and magnetic 
properties of the natural substance, and deceiving artists to 
whom it was presented as such. “It appears to be a condition,” 
says the experimenter, “ in converting a stone into pumice, that 
it should contain a volatile substance, which can only be removed 
by the same degree of heat which is at the same time necessar 
for producing that sort of semi-vitrification in the mass ich 
renders it coherent, hard, and porous.” Some greenstone, 
which had lost 1-25 per cent. by ignition, was treated as the pitch- 
. stone had been, and became converted, partly into a vesicular 
glass, and partly into pumice. 
~ XXV. Observations on the Changes the Egg undergoes during 
Incubation in the common Fowl; illustrated by microscopical 
Drawings. By Sir Everard Home, Bart. VPRS. 
In this communication, the progress of the formation of the 
chick is traced, “step by step, from the first appearance 
of the molecule found on the yolk before it leaves the ovarium 
to the complete evolution of all its parts, and its leaving the 
shell.” The details are illustrated by a series of microscopical 
delineations by Mr, Bauer, and cannot usefully be given without 
them. —— 
~Sir Everard proceeds to illustrate from the results of the 
investigation, the processes by which the human fetus and that 
of quadrupeds are formed, some circumstances being common 
to them; and those employed in the bird. 
© XVI. Some Observations on Corrosive Sublimate. By John 
Davy, MD. FRS. 
‘Dr. Davy commences this paper by observing, “ f am not 
