Chemistry and Physics. 419 
For all values Jess than 1°517 and therefore for 1:506, equation (4.) 
gives imaginary values for 4. But by taking into consideration the influ- 
ence which the ponderable particles exert upon the atoms of the ether 
which was neglected by Cauchy, Redtenbacher develops the formula 
aga be, (5.) 
This formula agrees with observation very well within the limits of 
the visible spectrum, When applied to Miiller’s index of refraction 1°506 
for the extreme heat rays it gives for the corresponding wave length 4 the 
value 0:0048™™, which is more than twice as great as that above deter- 
mined by the author. Miiller remarks that this difference is not surpris- 
ing when we consider how uncertain is the application of empirical for- 
mulas far beyond the limits for which their coefficients are determined. 
In any event the value 4—=0-0048™™ js much nearer the truth than that 
deduced from the purely empirical formula. If we adopt this determin- 
ation, 0-0048mm for the wave length of the extreme dark rays of heat, 
ve find that the entire solar spectrum embraces four complete octaves, of 
which not quite one is made up of the visible spectrum.—Pogg. Ann., 
tY, 837, 543, W. G. 
‘pon the oxyd- of chromium. He mixed together one equivalent of each 
Sdstance in fine powder, and heated the mixture in a — mri 
When the evolution of gas had ceased and the mass was more strongly 
heated, it fused, and on cooling furnished a radiately crystalline body 7 a 
dark reddish-brown color, which, when triturated, gave a brownish-yellow 
powder, and proved to be pure chromate of lead. When this salt is ba 
pia elementary analyses, it is principally only the chromic acid that 
a ved of its oxygen; and used chromate of lead may be again — 
He into the pure salt by moistening it with nitric acid and afterw 
ing it. 
ms ‘May, 1858 
1 and Acetic Acid ; by R. Fresenius, (Liebig’s Annalen, May, ’ 
en Cited from Clams, Gable, No. 381, p. 338).—According to the 
