66 Screntific Intelligence. 
ride is hereng volatile as such.—Ber. Berl. Chem. Ges., xii, a 
Nov., 1879. G. 
3. On the preparation of the Acetic ethers of Poiydiomie. ‘Ale 
hols.-FRaNcuHIMONT has shown that by making use of the dehy- 
drating powers of zinc chloride, acetyl derivatives of the higher 
polyatomic alcohols can be obtained with ease. The ca arbohy- 
drate is warmed with four times its weight of acetic oxide and a 
small fragment of fused zinc chloride. The acetylization is com- 
e, as experiments with cellulose, mannite, and glycerin have 
satisfactorily shown.—Ber. Berl. Chem. Ges. Uy ea, oe a ov., 
1879. 
4. On the Relation tee ep ante! Refractive Powe per 
Chemical Constitution.—Brtu has continued the investigations 
of Gladstone and Landolt with srt to the relation between 
refractive power and chemical constitution, and has obtained some 
interesting results. The researches of these chemists had shown 
that the expression TR , in which » is the refractive index and 
d the density, possesses a value for any given substance, which is 
independent of the temperature. vat ee o had multiplied this by 
the molecular weight, obtaining P *S* which he called the 
molecular refractive power. For feebly refractive media n may 
represent any definite index, such as, for example, that of H,, the 
red line of hydrogen. But in order to compare substances which 
are highly refractive, as to their refractive power, none 0 
observed indices will answer, as they are all influenced by disper- 
sion. A refractive index not thus affected would be the index 
corresponding to a ray of infinitely great wave-length. is 
Landolt finds as follows: Calling fy, the index for light of wave- 
length A, and yy, for that of wave-length A,, the formula of Cau- 
chy gives, for substances not too highly vatractive: 
B B 
Kh= A a and Kh, = Arya: 
Hence we have ; ‘ 
te 1 and A=, - 3 
in which B is the ootiicient of dispersion and A the index desired 
of a ray of infinitely great wave-length. Substituting this last 
value for n in the formula above, we have the expression zone 
constant for the same substance, dependent only upon the chemical 
character of the body and independent of its ‘density and disper- 
sion, as also of temperature. The product of this by the molecu- 
lar weight, P(=5+), Brihl calls the molecular refraction. The — 
