Soundness of Precious Stones.—Patents. 235 
taleareous stone formed by simple deposition, and by imperfect 
crystallization ; it is just such as might reasonably be expected 
to be formed in the vicinity of a voleano, where the solvent was 
considerably above the natural temperature of water, and much 
below that of metallic fusion. 
SOUNDNESS OF PRECIOUS STONES. 
It is of great importance to lapidaries, and purchasers of pre- 
cious stones, to possess some means of ascertaining their sound- 
ness or freedom from flaws when iu the rough state. Hitherto 
artists had no rule to direct their judgement in this respect, and 
have in consequence often sustained much loss. To remedy this 
defect, Dr. Brewster proposes the following method: Immerse 
the rough unwrought stone in Canada balsam, oil of sassafras, 
or any other fluid of nearly the same refractive density (as oil of 
anise seeds) and turn it round with the hand so that the rays of 
light may pass through it in every direction. By this means the 
slightest flaws or cracks may be instantly perceived in conse- 
auence of the changes which they produce on the transmitted 
light. If the stone be examined in water the flaws become more 
perceptible than when viewed in the air; and the distinctness 
with which they are seen increases as the refractive powers of 
the fluid approach that of the solid. Thus diamond jargon, 
spinelle ruby, &c. which exceed any fluid in refractive power, 
have their imperfections detected when immersed in oil of cassia 
or muriate of ammonia. Natural and artificial stoves may be 
likewise discriminated by oil of cassia, as the refractive powers of 
diamond, jargon, ruby, garnet, pyrope, sapphire, tourmaline, 
rubellite, pistazite, axinite, cinnamon stone, chrysoberyl, and 
chrysolite, exceed it. If an object be viewed through two po- 
lished and inclined surfaces, of any substance supposed to be 
one of these minerals, when plunged in oil of cassia, the sub- 
stance is a paste or artificial stone if the refraction is from the 
point to which the surfaces are inclined, and a real mineral when 
the refraction is made ¢owards that point. The soundness and 
purity of glass for lenses may be ascertained in a similar man- 
ner. 
LIST OF PATENTS FOR NEW INVENTIONS. 
To William Stocker, of Martock, in the county of Somerset, 
gunsmith, for a cock made of metal and wood, for dr awing 
liquor from casks, which produces stop superior to that which is 
effected by common cocks, and prevents the liquor from coming 
in contact with the metals, except when the liquor is in the act 
of being drawn, and is running from the cask.—10th January, 
1814,.—2 months. 
To 
