1.3S 



CHEMISTRY. 



Competi- 

 tion. 



T|, e component part* of bones ire chiefly four ; name- 

 ly, the earthy nits, fat, gelatine, and cartilage. 



1. The earthy lalts may be obtained either by calcin. 

 ing the bone to whiteneu, or by steeping it for a suf- 

 ficient length of time in acids. In the first case, the salts 

 remain in the state of a brittle white substance ; in the 

 second they are dissolved, and may be thrown down by 

 the proper precipitant*. These earthy salts are four in 

 number : 1. Phosphate of lime, which constitutes by far 

 the greatest part of the whole. 2. Carbonate of lime. 

 3. Phosphate of magnesia, lately discovered by Fourcroy 

 and Vauquelin. It occurs in the bones of all the inferior 

 animals examined by these indefatigable chemists, but 

 could not be detected in human bones. 4. Sulphate of 

 lime, detected by Mr Hatchett in a very minute propor- 

 tion. 



2. The proportion of fat contained in bones is various. 

 By breaking bones in small pieces, and boiling them for 

 some time in water, Mr Proust obtained their fat swim- 

 ming on the surface of the liquid. It weighed, he says, 

 one-fourth of the weight of the bones employed. This 

 proportion appears excessive, and can scarcely be ac- 

 counted for, without supposing that the fat still retained 

 water. 



3. The gelatine is separated by the same means as the 

 fat, by breaking the bones in pieces and boiling them 

 long enough in water. The water dissolves the gelatine, 

 and gelatinizes when sufficiently concentrated. Hence 

 the importance of bones in making portable soups, the 

 basis of which is concrete gelatine, and likewise in ma- 

 king glue. By this process, Proust obtained from pow- 

 dered bones about one-sixteenth of their weight of gela- 

 tine. 



4-. When bones are deprived of their gelatine by boil- 

 ing them in water, and of their earthy salts by steeping 

 them in diluted acids, there remains a soft white elastic 

 substance, possessing the figure of the bones, and known 

 by the name of cartilage. From the experiments of 

 Hatchett, it appears that this substance has the proper- 

 ties of coagulated albumen. Like that substance, it be- 

 comes brittle and semitransparent when dried, is readily 

 soluble in hot nitric acid, is converted into gelatine by 

 the action of diluted nitric acid ; for it is soluble in hot 

 water, and gelatinises on cooling, and ammonia dissolves 

 it and assumes a deep orange colour. 



Ox bones, according to the analysis of Fourcroy and 

 Vauquelin, are composed of 



51.0 solid gelatine. 



37.7 phosphate of lime. 



10.0 carbonate of lime. 



1.3 phosphate of magnesia. 



100.0 



From tlic calcmed bones of horses and sheep, fowls, and 

 tishcs, they extracted about one-thirtysixth part of phos- 

 phate of magnesia. More lately, these eminent chemists 

 detected the same constituents in human bones. 



The only bone hitherto observed altogether destitute 

 of cartilage is the enamel of the teeth. When the rasp- 

 ings of bones are steeped in diluted acids, the cartilage 

 alone remains undissolvcd. Now, when the raspings of 

 enamel arc treated in this manner, Mr Hatchett observed, 

 that the whole was dissolved without any residuum what- 

 ever. If we believe Fourcroy and Vauquelin, the enamel 

 f teeth it composed of 



72.9 phosphate of lime. 



27.1 gelatine aud water. 



100.0 



But the most complete analysis of teeth has been nude Chemical 

 by Mr Pepys, and his results agree exactly with those Examiua. 



or Hatchett. He found the enamel of the teeth com. lion of 



Noiure. 



posed of 



78 phosphate of lime. 

 6 carbonate of lime. 

 16 loss and water. 



100 



2. Shells. 



Under the name of tht-lls we include all the bony co- Shells, 

 verings of the different species of shell fuh. Egg shells, 

 aUo, from the similarity of their texture, belong to the 

 same head. For almost all the knowledge of these sub- 

 stances that we possess, we are indebted to the late im- 

 portant dissertations of Mr Hatchett. A few detached 

 facts, indeed, had been observed by other chemists ; but 

 his experiments gave us a systematic view of the consti- 

 tuents of the whole class. 



Shells, like bones, consist of calcareous salts united to 

 a soft animal matter ; but in them the lime is united 

 chiefly to carbonic acid, whereas in bones it is united to 

 phosphoric acid. In shells, the predominating ingredient 

 is carbonate of lime ; whereas in bones, it is phosphate of 

 lime. This constitutes the characteristic difference in 

 their composition. 



Mr Hatchett has divided shells into two classes. The 

 first are usually of a compact texture, resemble porcelain, 

 and have an enamelled surface, often finely variegated. 

 The shells belonging to this class have been distinguished 

 by the name of porce/aneovs shells. To this class be- 

 long the various species of valuta, cyjyrcca, &c. The 

 shells belonging to the second class are usually covered 

 with a strong epidermis, below which lies the shell in 

 layers, and composed entirely of the substance well known 

 by the name of mother-of-pearl. They have been dis- 

 tinguished by the name of mother-of-]tearl shells. The 

 shell of the fresh water muscle, the haliotis iris, the turbo 

 olearius, are examples of such shells. The shells of the 

 first of these classes contain a very small portion of soft 

 animal matter ; those of the second contain a very large 

 portion. Hence we see that they are extremely different 

 in their composition. 



1. Porcclaneous shells, when exposed to a red heat, porcrlane* 

 crackle and lose the colour of their enamelled surface, ous shclU. 

 They emit no smoke or smell ; their figure continues un- 

 altered, their colour becomes opake white, tinged par- 

 tially with pale grey. They dissolve when fresh with 

 effervescence in acids, and without leaving any residue ; 



but if they have been burnt, there remains always a little 

 charcoal. The solution is transparent, gives no precipi- 

 tate with ammonia or acetate of lead ; of course it con- 

 tains no sensible portion of phosphate or sulphate of 

 lime. Carbonate of ammonia throws down an abundant 

 precipitate of carbonate of lime. Porcelaneous shells, 

 then, consist of carbonate of lime cemented together by 

 a small portion of an animal matter, which is soluble in 

 acids, and therefore resembles gelatine. 



2. Mother-of-pearl shells, when exposed to a red heat, Mother-of- 

 crackle, blacken, and emit a strong fetid odour. They pearl shell*, 

 exfoliate, and become partly dark grey, partly a fine 



white. When immersed in acids they effervesce at first 

 strongly ; but gradually more and more feebly, till at 

 last the emission of air-bubbles is scarcely perceptible. 

 The acids take up only lime, and leave a number of thin 

 membranous substances, which still retain the form of 

 the shell. From Mr Hatchett's c xperiments we learn, 

 that these membranes have the properties of coagulated 



