CHEMISTRY. 



139 



Chemical 

 Examina- 

 tion of 

 Nature. 



Peart. 



Crusts. 



Horn i. 



Jfcilt. 



albumen. Motlier-of- pearl shells, then, are composed of 

 alternate layers of coagulated albumen, and carbonate of 

 lime, beginning with the epidermis, and ending with the 

 last formed membrane. 



Pear!, a well known globular concretion which is 

 formed in some of these Bhells, resembles them exactly in 

 its structure and composition. It is a beautiful substance, 

 of a bluish white colour, iridescent, and brilliant. It is 

 composed of concentric and alternate coats of thin mem- 

 brane and carbonate of lime. Their iridescence is obvi- 

 ously the consequence of the lamellated structure. 



3. Cruits. 



By crusts we understand those bony coverings of 

 which the whole external surface of crabs, lobsters, and 

 other similar sea animals are composed. Mr Hatchett 

 found them composed of three ingredients: 1. A carti- 

 laginous substance, possessing the properties of coagu- 

 lated albumen 5 2. Carbonate of lime ; 3. Phosphate of 

 lime. By the presence of this last substance they are es- 

 sentially distinguished from shells ; and by the great ex- 

 cess of carbonate of lime above the phosphate, they are 

 equally distinguished from bones. Thus the crusts lie 

 intermediate between bones and shell-', partaking of the 

 properties and constitution of each. The shells of the 

 eggs of fowls must be referred likewise to the chss of 

 crusts, since they contain both phosphate and carbonate 

 of lime. The animal cement in them, however, is much 

 smaller in quantity. From the experiments of Bemiard 

 and Hatchett, it is extremely probable that the shells of 

 snails are composed likewise of the same ingredients, 

 phosphate of lime having been detected in them by these 

 chemists. 



SECT. II. Of Horns, Nails, and Sealer. 



In the last Section we treated of those hard parts of 

 animals which were inflexible and incapable of being 

 oftened by heat, and which contained a great portion of 

 calcareous salts ; but there is another set of hard parts 

 which possess considerable elasticity, which are softened 

 by heat, and which contain but a very small portion of 

 calcareous matter. This set comprehends the substances 

 well known under the names of horn, ni/s, and tcalet. 



1. Horns are well known substances that are attached 

 to the foreheads of oxen, sheep, and various other animals. 

 They are not very hard, as they may be easily cut with 

 a knife or rasped with a file ; but they are so tough, as 

 not to be capable of being pounded in a mortar. When 

 in thin plates, they have a degree of transparency, and 

 have been sometimes substituted for glass in windows. 

 When heated sufficiently they become very soft and flex- 

 ible, so that their shape may be altered considerably. 

 Hence they may be gradually squeezed into a mould, 

 and wrought into various fonns, as is well known. When 

 strongly heated in a Papin's digester, they are said to be 

 converted into a gelatinous mass, which possesses the 

 properties of gelatine. 



The quantity of earthy matter which they contain is 

 exceedingly small. Mr Hatchett burnt 500 grains of 

 ox horn. The residuum was only 1.5" grain, and not the 

 half of this was phosphate of lime. Seventy-eight grains 

 of the horn of the chamois left only 0.5 of residue, of 

 which less than the .half was phosphate of lime. They 

 consist chiefly of a membranous substance, which pos- 

 sess the properties of coagulated albumen ; and probably 

 they contain also a little gelatine. 



2. The nails, which cover the extremities of the fingers, 

 are attached to the epidermis, and come off along with 



it. Mr Hatchett has ascertained that they are composed Chemical 

 chiefly of a membranous substance, which possesses the l 

 properties of coagulated albumen. They seem to con- Nature, 

 tain also a little phosphate of lime. Water softens, but s^-y^^ 

 does not dissolve them ; but they are readily dissolved 

 and decomposed by concentrated acids and alkalies. 

 Hence it appears that nails agree with horn in their na- 

 ture and composition. Under the head of nails must be 

 comprehended the talons and claws of the inferior ani- 

 mals, and likewise their hoofs, which differ in no respect 

 from horn. 



3. Scales of animals are of two kinds ; some, as those Scale?, 

 of serpents and other amphibious animals, have a striking 

 resemblance to horn ; while those of fish bear a greater 

 resemblance to mother-of-pearl. The composition of 

 these two kinds of shells is very different. 



The scales of fish are composed of different membra- 

 nous lamina;. When immersed for four or five hours in nitric 

 acid, they become transparent, and perfectly membrana- 

 ceous. The acid, when saturated with ammonia, gives 

 a copious precipitate of phosphate of lime. Hence they 

 are composed of alternate layers of membrane and phos- 

 phate of lime. To this structure they owe their bril- 

 liancy. Mr Hatchett found the spicula of the shark's 

 skin to be similar in its composition, but the skin itself 

 yielded no phosphate of lime. 



The horny scales of serpents, on the other hand, are 

 composed alone of a horny membrane, and are destitute 

 of phosphate of lime. They yielded, when boiled, but 

 slight traces of gelatine; the horn-like crusts which 

 cover certain insects and other animals, appear, from Mi 1 

 Hatchett's experiments, to be nearly similar in their com- 

 position and nature. 



SECT. III. Of the Muscles of Animals. 



After the hard parts of animals have been examined, Muscles *f 

 it remains for us to consider the composition of the soft animals, 

 parts. Of these, the muscles naturally claim our atten- 

 tion in the first place, as being the most important. 



The muscular parts of animals are known, in common 

 language, by the name ofjlcsh. They constitute a con- 

 siderable portion of the food of man. 



Muscular flesh is composed of a great number of fibres 

 or threads, commonly of a reddish or whitish colour ; but 

 its appearance is too well known to require any descrip- 

 tion. Hitherto it hat not been subjected to any accu- 

 rate chemical analysis. 



When a muscle is cut in small pieces, and well washed 

 with water, the blood and other liquids contained in it 

 are separated, and part of the muscular substance also is 

 dissolved. The muscle, by this process, is converted 

 into a white fibrous substance, still retaining the form of 

 the original body. The water assumes the colour which 

 results from mixing water with some blood. When 

 heated it coagulates ; brown flakes swim on the surface, 

 consisting of albumen combined with the colouring mat- 

 ter of the blood : some fibrin likewise precipitates. If 

 the evaporation be continued, more albumen precipitates, 

 and at last the whole assumes the form of a jelly. Whea 

 evaporated to dryness, and treated with alcohol, the ge- 

 latine thus formed, together with a little phosphate of 

 soda and of ammonia, remains undissolved ; but the al- 

 cohol dissolves a peculiar extractive matter, first ob- 

 served by Thouvenel. This matter may be obtained 

 by evaporating the alcohol to dryness. It has a red- 

 dish brown colour, a strong acrid taste, and aromatic 

 odour. 



If the muscle, after being thuj treated with cold wa- 



