1874.] Beryls and Emeralds. 507 
variation in hue. The dichroism of other coloured beryls, 
as well as the emerald, is often well marked. 
One of the main objects for which Greville Williams’s 
research was undertaken was the settlement of the relation 
between the so-called organic matter found in the emerald 
and the colour of the stone. By an ingenious arrangement 
of apparatus, and by the use of the chromic acid method of 
burning the carbon and hydrogen present, this chemist has 
shown that colourless beryls sometimes contain carbon and 
hydrogen, just as the emerald does; and he has demon- 
strated that the carbon does not exist as a carbonate, though 
it may possibly occur in the form of microscopic diamonds. 
We are promised a further contribution to the chemistry of 
the emerald, with especial reference to the modes of sepa- 
rating and estimating the rare earth, glucina, which it—in 
common with the chrysoberyl, another mineral used in 
ornamental jewellery—also contains. The chemist Loewy, 
who believed the colour of the emerald to be due to organic 
matter, detected the earth glucina, to the extent of 4 per 
cent, in the calcareous concretions which are associated 
with the matrix in which the mineral is found at Muzo, 
New Granada: pyrites, and the rare carbonate of the 
cerium metals known by the name of Parisite, also occur 
with the emerald. It would be as well to examine the 
Brazilian emerald for cerium and its allies. 
The emerald is more prized now than formerly, as much 
as £40 having been given for a perfect emerald of 1 carat 
(0°20541 of a gramme, or 3°17 grains). An emerald of 
I carat, owing to its low specific gravity, is of course much 
larger than a sapphire of the same weight, and about one- 
third larger than a diamond. Large emeralds are seldom 
of uniform and deep colour, and hardly ever free from 
numerous cavities and flaws. In the Duke of Devonshire’s 
collection there is a splendid crystal, about 2 inches in each 
direction, and weighing nearly 9 ounces troy, but it is much 
flawed. Inthe Green Vaults of Dresden there are some fine 
stones, while there are also numerous specimens in the 
Brazilian, Turkish, Portuguese, Austrian, Persian, and Papal 
Treasuries. Many of these have, however, been disfigured 
by perforations or inartistic engravings, and being in many 
cases merely rounded and polished, ‘‘ en cabochon,” are not 
capable of showing to full advantage those optical properties 
of dispersion, refraction, dichroism, &c., which may be deve- 
loped by the judicious cutting of this gem. In the South 
Kensington Museum, among the rings of the Townshend 
collection, is a superb emerald, step-cut, and showing the 
