74'2 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



according to the nature of the parts of animals which, singly or conjointly, they 

 are employed to form. In these bodies the quantity of the saline substances 

 appears to be diminished, while that of the earthy matter is increased, especially 

 in the coarser kinds of muscular fibre. 



On a comparison of the chemical properties of the substance which remains, 

 after the separation of gelatin from the great variety of animal substances which 

 have been so often mentioned in the course of this paper, and which need not 

 therefore now be repeated, there can scarcely be any doubt but that it is one and 

 the same substance, in different states of density and texture. For the similarity 

 of its nature was proved by, 1st. The effects of fire, and the products obtained by 

 distillation. 2dly. Its very difficult solubility by long digestion in boiling water. 

 3dly. The effects produced by re-agents, on the water in which bodies like inspis- 

 sated albumen or tortoise-shell had been boiled. 4thly. The effects of acids, 

 particularly nitric acid, of ammonia, and of caustic lixivium of potash. 5thly. 

 The animal soap which was formed ; and the precipitate obtained from it, by the 

 addition of acetous or muriatic acid*. Gthly. The difficulty attending the putre- 

 faction of the substance in question, when pure and dense. The similarity in all 

 these properties, appears to be a full proof, that it is the same substance which 

 constitutes the principal part of membrane, sponge, horn, hair, &c. and even of 

 muscular fibre. 



Besides, on comparing the properties of this substance with those of pure 

 albumen in a state of inspissation, so evident a resemblance in every respect is dis- 

 covered, that few I believe will hesitate to pronounce albumen to be the original 

 substance from which tortoise-shell, hair, horn, muscular fibre, &c. have been de- 

 rived and formed. There is much reason to believe that gelatin, though it appears 

 so different in many respects from albumen, is yet formed from it-f~. 



* This appears to be a strong marked character of the albuminous substances. + In addition to the 



chemical properties by which gelatin and albumen are distinguished, particularly the different effects 

 observed when these 2 substances were treated with nitric acid, I shall mention some others, not less 

 remarkable, which are produced by the muriatic acid. When any of the varieties of gelatin, such as 

 glue, isinglass, &c. are immersed in cold muriatic acid, they are dissolved in a few hours ; and the 

 solutions thus formed surfer no apparent change, even in the course of several months. In like 

 manner, gelatin may be separated and dissolved from bodies which contain it, such as sponge, bladder, 

 skin, and muscle ; but the part which remains undissolved, and which, with the other substances 

 formerly mentioned, I regard as formed of albumen more or less organized, is very differently affected; 

 for when coagulated albumen, the undissolved part of bladder, muscular fibre, feather, quill, tortoise- 

 shell, wool, and hair, were separately steeped in muriatic acid, they gradually became of a dark 

 colour, and the acid was tinged with the same. The colour afforded by albumen was deep 

 blue, inclining to purple ; that of bladder was brownish purple ; feather, quill, tortoise-shell, 

 and muscular fibre, afforded a beautiful deep blue ; and wool, and hair, like bladder, produced 

 a brownish purple. The change began to take place in the coagulated albumen in about 8 or 10 

 days; but wool and hair were the last affected. In about 3 months, the different liquids were become 

 very dark, though scarcely any perceptible quantity of the immersed substances appeared to be dis- 

 solved. Nitric acid, in a small proportion, changed these blue and brownish purple liquors to deep 

 yellow ; and ammonia, being then added, changed them to orange colour, and produced all those 

 effects which were observed, when the nitric solutions of these substances were thus treated. — Orig. 



