M. C. Lea on the Platinum Metals. 81 
and 
A” cos 8” cos (1 — @) — RY = r"’ cos b” cos (l”—O") 
A” cos 8” sin (4/— ©”) = r" cos b” sin (l/— ©") 
A” sin 8” <—.s? Git er 
The values of r and r” found from these formule must agree 
with those found previously. 
Having now the heliocentric codrdinates of the comet - the 
t 
the assumption of log A gives W/--a and §’+5 
6“ ry log A +i “ ia! “ Bib! 
but 
. . log A+-z must give¥ “ fF 
therefore neglecting second differences we must have 
a’ ~_ — 
a a 
From as many such equations as we choose to employ we may 
determine x, and a new computation assuming log A+ as the 
logarithm of the distance between first comet and first earth, 
will lead to our desired improved elements. 
Art. IX.—Notes on the Platinum Metals, and their Separation 
Jrom each other ; by M. Carey Lua, Philadelphia —Part I. 
(I.) : 
FEw branches of inorganic chemistry present difficulties com- 
parable with those involved in the study and separation of the 
Platinum metals, Their close analogy with each other, and the 
Temarkable manner in which the relations of each to chemical 
Feagents are controlled by the presence of the others, give rise 
to difficulties in their detection and separation which are only by 
deg ing surmounted. h time and unwearied labor 
on the part of the chemist are required to reach results which 
When obtained appear insignificant in proportion to the effort 
Which they cost, and it may in fact be said that the platinum 
Metals constitute a chemistry in themselves, governed by speci 
Tules and to be studied by special methods. Each step in the 
Simplification of the processes by which the separations are 
F % 
effected, each decisive reaction by which the presence or ab- 
Sence of a member of the group may be certainly inferred, is so 
‘Much gained toward conquering a complete knowledge of these 
‘Tare and interesting bodies. 
| Scr. 
Te and 1 
_ AM. Jour. Sct.—seconp Serres, Vou. XXXVIII, No, 112—Juty, 1864, 
: ll 
