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428 Diamonds. [ July, 
unequally distributed. Yellow, green, brown and gray are the 
colors most frequently observed. According to Brewster, many 
of the diamonds showing cavities under the microscope afford 
evidence, upon polarization, of having been subjected to pressure 
near these cavities at the time the diamond was crystallized. 
Such cavities, and slight accumulations of coloring matter were 
at first erroneously designated as chlorophylloid substances. 
Yellow and brown diamonds owe their color probably to avery © 
minute percentage of hydrated ferric oxide. It is an expensive 
amusement to analyze a quantity of diamonds sufficiently great 
to determine this point, so we are forced to base an opinion upon 
other than analytical proof. In the beginning of the nineteenth 
century a Parisian jeweler heated a brown diamond for some 
time, and, upon taking it out of the crucible, found that it had 
burned pink. This color, however, only lasted for about ten days, 
when the stone turned brown again. Since that time the experi- 
ment has been repeatedly tried, often with the same result. The 
chemical action in this instance consisted simply in driving off 
the water, so that the iron was contained in the diamond as ferric 
oxide. This imparts a pink color. Upon exposure to ordinary 
atmosphere, the original hydrated ferric oxide was again formed. 
Green diamonds probably owe their color to an indefinitely small 
quantity of ferrous oxide. Whether the Dresden diamond is 
‘colored by the same material may remain an open question. The 
shade of green it exhibits is not one that would probably be pro- 
duced by ferrous oxide. Possibly some organic salt of iron may 
produce the effect of color. 
Gray diamonds usually owe their lack of transparency to the 
presence of innumerable microscopic cavities. 
What the coloring matter of the Hope diamond may be can 
scarcely more than be guessed at. From analogy we know that 
certain salts of iron, organic matter and cobalt produce the same 
color. Which of these it is will most likely remain a secret. Ata 
venture, the salts of iron might seem the most probable, consider- 
ing the uniformity of coloring and the shade of the blue. 
Regarding the formation of diamonds much has been said and 
written, and many- well-conceived experiments have been made. 
More than any other agent, heat has been employed to reproduce 
i, : these treasures of nature’s laboratory. Thus far all experiments 
have failed to attain any available result. Some of the most emi- 
