734 PHILOSOPHICAL TRANSACTIONS. [ANNO ] 800. 



been boiled, is steeped in a dilute acid, (especially nitric acid,) the ossifying sub- 

 stance is dissolved, and, at the same time, but more slowly, the gelatin is sepa- 

 rated, and causes the liquor to become yellow, when the phosphate of lime is pre- 

 cipitated by ammonia. The cartilaginous body which remains, after the gelatin has 

 been thus separated, is not easily soluble in dilute acids, for, according to its 

 texture, many weeks, and even months, may elapse, before a small part is taken 

 up; but in concentrated nitric acid, or in boiling dilute acid, it is rapidly dissolved. 

 This substance, when dry, is semi-transparent, like horn, and more or less brittle. 

 It is the predominant and essential part, in the tissue or web of membrane, carti- 

 lage, sponge, the horny stems of gorgoniae, horn, hair, feather, quill, hoof, nail, 

 horny scale, crust, and tortoise-shell ; and, though of similar chemical properties, 

 yet in consistency it varies, from a tender jelly-like substance, to a completely 

 formed membrane, or to an elastic, brittle, and hard body, like tortoise-shell*. 



Experiments were made separately, on each of the bodies above enumerated; 

 but as I did not find any essential difference in the results, I shall include the 

 whole under the following observations. 1. When distilled, a small portion of 

 water, some carbonate of ammonia, a foetid empyreumatic oil, carbonated hydro- 

 gen gas, carbonic acid gas, and prussic acid, were obtained. 1. A spongy coal, 

 of a gray metallic lustre, remained : this; by incineration, afforded a very small 

 residuum, which was not always similar in quantity, even in portions of the same 

 substance; for, 500 gr. of tortoise-shell, taken from different samples, afforded 

 from -J- of a gr. to 3 gr. of residuum, which consisted of phosphate of lime, and 

 phosphate of soda ; sometimes also a little carbonate of lime was present; but I 

 do not believe these to be essential ingredients. 3. When boiled many days in 

 distilled water, the substance was softened ; and the water became slightly turbid 

 with nitro-muriate of tin; but no effect was produced by the tanning principle. 



4. Muriatic and sulphuric acids had little effect, unless heated; and the same was 

 the case with nitric acid much diluted, or in the state proper to extract and sepa- 

 rate gelatin ; but if the immersion in the dilute acid was continued during some 

 weeks, the acid gradually acquired a yellow tinge, and, when saturated with am- 

 monia, became of a deeper colour, without having its transparency disturbed. 



5. The substance which had thus been long steeped in the acid, was much softened, 

 was become more transparent, and, from being horny, was now more like a car- 

 tilaginous substance: when taken out of the acid, if it was immediately steeped in 

 pure ammonia, it changed to a deep orange colour, inclining to blood red; it was 

 gradually and silently dissolved, without any residuum, and a deep orange or yel- 

 lowish brown coloured liquor was formed. 



• These bodies, especially tortoise-shell, appear to be formed, as far as organic arrangement is con- 

 cerned, in the way of stratum super stratum. This structure is peculiarly to be discovered after long 

 maceration in diluted nitric acid; for then, tortoise-shell appears to be composed, like the black 

 polished gorgenia, of membranaceous laminae ; and the varieties of horn differ only by a tendency to 

 the fibrous organization. — Orig. 



