Astronomical and Nautical Collections. 415 
P. L, 15 47, Half sum 1.8460 
P. L. for. HM. 3501 
3501 
P.L. 22’ 16” 9076 P.L. Semid.5™ 45: 1.4959 
10 3 26 
P.L. 49m 52s ‘ 5575 
10 53 18 9 57 41_Immersion 
10 9 11 Emersion 
10 3 26 Middle = 
The effect of the earth’s ellipticity appears therefore to 
shorten the duration from 15™ 16° to 11™ 30°, the difference 
being 3™ 46°, as derived from the consideration of the ‘‘ Geo- 
centric” instead of the true latitude. 
Art. XVI. PROGRESS OF FOREIGN SCIENCE. 
CHEMICAL SCIENCE. 
1. Laws or COMBINATION. 
On the Relation which exists between Crystalline Form and Che- 
mical Proportions. By Mr. E. Mitscherlich. 
(Continued from page 219.) 
Of the Phosphate and Arseniate of Potash and Soda. 
If we add carbonate of soda to the bin-arseniate, or bi-phos- 
phate of potash, till we obtain neutral salts, the solutions 
crystallize entirely, as double salts. The solutions of the crys- 
tals precipitate muriate of barytes so that the liquid is neutral, 
and comport themselves with solutions of the metallic oxides 
like the neutral arseniates and phosphates. They are conse- 
quently at the same degree of saturation as these salts. 
100 parts of this double phosphate consist, according to 
Berzelius, of 
Phosphate of potash . . 27.38 
———-—- soda. . . 22.12 
Water. ... 50.50 
100 parts of the double Arseniate are composed, by the same 
authority, of . Arseniateofpotash . 30.24 
—-soda . . 26.65 
Water) }2 70). 4+ aie ti ni A4 DE 
The primitive form of these two salts is an oblique prism with 
rhombic bases ; a figure often met with, without any modifica- 
tion, 
