238 The Rev. Joun Horuz's Observations on A rragonite, 
particles are chemically combined with the constituents of the 
mineral, being uniformly diffused through the whole mass. 
Experiment 3.—One small specimen of calcareous spar, and an- 
other of Arragonite, about the same size, were placed at the same 
instant on a plate of iron heated to redness. The thickness of the 
plate somewhat exceeded half an inch. The former specimen 
began almost immediately to decrepitate and disperse, whilst the 
other remained unaltered; but afterwards acquiring a greater de- 
gree of heat, the Arragonite fell gradually to powder. This experi- 
ment proves that the water is retained more strongly in the Arra- 
gonite than it is in the calcareous spar ; from which eircumstance 
the same inference may be made as before, viz. that water is 
chemically combined in the Arragonite, and only mechanically 
mixed in the other substance. This operation I have frequently 
. repeated with the same result, and also in a manner more precise 
as to the degree of heat required for expelling the water from 
each kind of calcareous spar. 
Experiment 4.—I took a part of a crystal of Arragonite, and, 
fixing it to the end of a wire, plunged it into boiling mercury, 
pm = ^ m - zn time. Upon withdrawing it, no 
change had taken place, the spar comine o | 
Br original nn TE s | = = sacra 
Experiment 5.—I then took a piece of common calcareous spar, 
which was part of a stalactite, and plunging it in the same man- 
ner as before into boiling mercury, it instantly decrepitated and 
flew to pieces, | 
Experiment 6.—Gypsum also tried in the same way lost its 
water of crystallization, which, as it was some time in coming 
away, gave to the mercury the appearance of violent ebullition 
from the escape of the water under it in the state of vapour. - 
Expe- 
