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Having thus briefly described the principal varieties of 
ivory which are in the market at present, I shall notice some 
experiments which have been made with a view to account 
for the difference of character we find in them. I may here 
observe that the results arrived at are to be understood as 
approximations merely, the experiments not having been 
made with the degree of accuracy which strict analysis 
would require, but they are sufficiently near for the purpose. 
In Hutton's Table of Specific Gravities, that of ivory is 
given at 1.825, and, by comparison, that of Indian ivory is 
1.7, and that of Egyptian 1.54. This difference in the 
specific gravity would indicate a greater degree of porosity 
in the two latter than in the African, whose specific gravity 
is greatest. In order to test their absorbent power, equal 
weights of each were soaked in water five hours; the African 
had then gained three per cent., the others upwards of five 
per cent, in weight. Equal weights of each, which had been 
exposed to the air some weeks, and may be said to have been 
in their natural state of dryness, were then exposed to the heat 
of boiling water for five hours, when the African had lost 
five per cent, of its weight, and the others between three and 
four per cent. 
From these experiments it appears that, in the ordinary 
state of the atmosphere, as to heat and moisture, African 
ivory contains more water than either of the other two 
varieties; that it absorbs water more slowly, and gives it 
off more slowly, when exposed to the same thermometric and 
hygrometric changes in the atmosphere. It is, therefore, 
less subject to expansion and contraction. This is to be 
understood only as it regards the ordinary changes in the 
atmosphere. A piece of ivory, of any description, if exposed, 
when newly cut or in a moist state, to a sudden elevation of 
temperature, would inevitably crack. 
I have been furnished with the following analysis by Mr. 
