33° Mr. Hatchett’s Experiments 
In like manner, if the effects produced by fire and acid men- 
strua, on shells composed of mother of pearl, and on the sub- 
stance of teeth and bone, are compared, a great similarity will 
be found ; for, when exposed to a red heat, 
ist. They smoke much, and emit a smell of burned cartilage, 
or horn. 
sdly. They become of a dark gray or black colour. 
3 dly. The animal coal thus formed is of difficult incineration. 
4 ,thly. They retain much of their original figure; but the 
membranaceous shells are subject to exfoliate.* 
^thly. These substances, (pearl, mother of pearl, tooth, and 
bone,) when immersed in certain acids, part with their harden- 
ing or ossifying substances, and then remain in the state of 
membrane or cartilage. 
6thly. When previously burned, and afterwards dissolved in 
acids, a quantity of animal coal is separated, according to the 
proportion of the gelatinous, membranaceous, or cartilaginous 
substance, and according to the duration of the red h at. 
And lastly, the acid solutions of these substances, by proper 
precipitants, afford carbonate of lime, in the one case, and phos- 
phate of lime principally, in the other, in a proportion relative to 
the membrane or cartilage with which, or on which, the one or 
the other had been mixed, or deposited. 
As porcellaneous shell principally differs from mother of 
pearl, only by a relative proportion between the carbonate of 
lime and the gluten or membrane, in like manner, the enamel 
appears only to be different from tooth or bone, by being desti- 
tute of cartilage, and by being principally formed of phosphate 
of lime, cemented by gluten. 
* This is a natural consequence, arising from their structure. 
