728 PHILOSOPHICAL TRANSACTIONS. [ANNO ] 800* 



to be much diminished, so that it easily gave way, and was broken. This effect, 

 Mr. Achard has also noticed ; * and I am induced to believe, from various experi- 

 ments which I have made on these substances, that the hair which loses its curl 

 in moist weather, and which is the softest and most flexible, is that which most 

 readily yields gelatin ; and, on the contrary, the hair which is very strong and 

 elastic, is that which affords it with the greatest difficulty, and in the smallest pro* 

 portion. These remarks have also been corroborated, by the assertion of a con r 

 siderable hair merchant in this metropolis j-, who, during a long experience of 

 upwards of 40 years, has always found, that hair of the first named quality cannot 

 be boiled an equal time with those last mentioned, without suffering material in- 

 jury in strength and flexibility. 



Feather, digested in boiling distilled water, during 10 or 12 days, did not afford 

 any trace of gelatin by the test of the tanning principle; but nitro-muriate of 

 tin produced a faint white cloud. The same was observed when quill was thus 

 examined. Shavings and pieces of the horns of different animals were next sub- 

 jected to experiment, and all afforded small quantities of gelatin, which was pre- 

 cipitated by the tanning principle, and by nitro-muriate of tin ; and it was gene- 

 rally observed, that the more flexible horns yielded the largest quantity of gelatin, 

 with the greatest ease ; and, like the substances already mentioned, when deprived 

 of it, and suffered to dry spontaneously in the air, they became more rigid, and 

 were easily broken. The horns which I mean, are those of the ox, ram, goat, 

 and chamois, which, in my former paper I considered, as I do now, to be per- 

 fectly distinct from the nature of stag's or buck's horn ; for this last is as different 

 from the former in chemical composition, as it is in construction : like bone, it 

 affords much phosphate of lime, and, like bone, it affords a large quantity of 

 gelatin ; and it is not a little remarkable, that phosphate of lime is generally ac- 

 companied by gelatin, as in stag's horn, bone, ivory, &c. on the contrary, when 

 carbonate of lime is the hardening substance, as in shells, madrepores, and mil- 

 lepores, no gelatin can be discovered ; for I have frequently digested these sub- 

 stances many days in boiling distilled water, after having reduced them to a coarse 

 powder that they might present a larger surface, but I never could by any test 

 discover the slightest vestige of gelatin. The horns therefore which were first 

 mentioned, are very different from the composition of stag's horn, and yield gra- 

 dually, and with great difficulty, only a small quantity of gelatin. 



Horny scale was next examined ; but I shall first here make a digression in 

 respect to the scales of fish, which I had not examined when my paper on shell 

 and bone was read. As the scales of fish, when viewed by a microscope, and 

 according to the observations of Mr. Leeuwenhoek, appear to be formed of dif- 



* " La perte de la partie gelatineuse otant aux cheveux leur souplesse, il s'ensuit que c'est aux 

 " parties gelatineuses qui entrent dans la composition des cheveux qu'ils doivent leur pliant et leur elas- 



" ticite." — Examen chimique des Cheveux, &c. Mem. de l'Acad. de Berlin, torn. 38. p. 12. f John 



Collide, Esq. of St. Martin's-lane. — Orig. 



