Chemistry and Physics. 111 
rd, otherwise whatever is condensed or projected upon it will flow 
downward and the product be contaminated, at least, with lead. Into 
this tube a smaller one of platinum is luted, which is bent into the shape 
of a quarter of a circle so that the farther end points downward ; this 
end is soldered with gold into the bottom of an inverted platinum eruci- 
ble. An old one, ipo and cracked, suc as is generally to be 
immersed in “water sank ed in a ear not very much ey Dea it in 
diameter, offers a large surface for the absorption of the acid gas, while 
a retrocession of the liquid from absorption or change of temperature is 
impossible. 
The cover to the retort may be cast in one piece with a shoulder, or be 
made of two discs of lead of the size of the inner and outer diameters of 
the bore, and held together by a ring of lead cast into them and serving 
asahandle. For a lute I spread a thin layer of gypsum on the surfaces 
in 9 ae ben cover the joint on the outside with a paste of rye-meal. 
2. Sky cldstok akan at Philadelphia; by Pursy Earte Caase, 
A.M., ‘PAB Reo ent observations with a —_ polariscope having — 
led me to results which, while generally confirm , differ in a few par- 
ticulars from those published by Sir David Brewster, (Phil. Mag. [4], xxx, 
pp. 118, 166, sqq.), I place some of them on record, to facilitate a com- 
(1.) In a the great circles which pass tharotek the sun, the polarization 
of a clea r sky is positive, sas in the neighborhood of the solar and 
anti-solar points. If the polariscope is rotated from the positive maxi- 
mum, the bands gradually diminish in brillianey, vanishing at about 45°, 
and attaining a negative maximum at about 90°. 
2 ) Within the primary lemniscates, of which the solar and anti-solar 
points are the respective centers, and the neutral points (actual or theo- 
Fea are the limits; the polarization of a clear sky is negative when 
the bands pass towa rd the sun's center, vanishing when re 
inclined re to the _~ bt and attaining a positive maximum when 
the Pereneny reaches 
’s and Babinet’s neutral points can be seen as well before 
sunrise as shee sunset, provided the atmospheric conditions are 
Brewster gives the preference to the evening observations, but =ppaeeae 
for no other reason yee that the sky is then usually clearer than in 
ae (op. cit. ; pel 
T hav ve reply, and with vas gs mcg difficulty, observed 
h 
as biter facility as that of Babinet’s. (For the difficulties of Brewste 
and Babinet, see loc. cit., pp. 119, 166, 181. 
(5.) Within the solar primary lemniseate it is frequently difficult to 
make any ordinary observation of the polarized bands, on account t of the 
dazzling intensity of the a But when the direct rays of the sun 
.F Proceedi rican Philosophical Soci 4g ay apne 
hes a rhe tine bar anil pons below che ane sol pele sot bona 
BBP cars x as Sak ig eaptllce to determ’ cette peau = 
