VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 737 



] 2. This precipitate, when collected on a filter, appeared more saponaceous, and 

 less viscid, than that obtained from the substances lately examined*. When 

 gently heated, some oil flowed from it ; after which a brownish viscid substance re- 

 mained, similar in its properties to that which was obtained from the animal soap 

 made by tortoise-shell and the other bodies-f-. 13. It may not be improper here 

 to repeat, that inspissated albumen, long boiled with distilled water, was not 

 apparently diminished ; but the water, like that in which tortoise-shell, quill, or 

 nail, has been boiled, had acquired the property of becoming white and turbid, 

 when nitro-muriate of tin was added, though it was not changed by the tanning 

 principle. To this also may be added, that the water in which tortoise-shell, nail, 

 and albumen, had been boiled, became in some measure putrid in a few days, 

 and emitted an offensive smell. 



I am not inclined however, to regard this as a proof that any gelatin had been 

 separated from these bodies by means of boiling water, but rather that inspissated 

 albumen, tortoise-shell, &c. are substances really soluble, though in so slight a 

 degree as to approach insolubility ; and that thus the prevalent opinion has arisen 

 concerning the insolubility of coagulated albumen in boiling water. Neither is 

 the putrefaction of the water in which the bodies abovementioned have been boiled, 

 a proof that any other than their real substance has been dissolved ; for this putre- 

 faction appears to depend on its attenuated and diluted state, more than on any 

 other cause. Tortoise-shell, nail, quill, and similar bodies, certainly are not liable 

 to putrefaction ; neither is albumen, when in the inspissated semi-transparent state. 

 This last substance also, when merely coagulated, does not easily putrefy ; for I 

 kept it, when it was soft, white, and coagulated, in water, during the whole of 

 the month of April, without finding that it became really putrid; towards the 

 latter part of the time, it had rather a disagreeable smell ; still however it was far 

 from being absolutely putrid. 



But albumen which has not been coagulated, or which has been diluted and 

 shaken with a quantity of cold water, begins in a very few days to be putrid ; 

 liquid albumen therefore enters easily into putrefaction, though it is the reverse 

 with that which is dense and solid : and from a comparison of the preceding ex- 

 periments on tortoise-shell, quill, nail, &c. with those made on albumen, I am 

 induced to believe that the former bodies are essentially composed of albumen, 

 modified by the various effects of organization, and reduced to a state of density 

 far exceeding that which is produced by simple inspissation. And though the 



* This precipitate, when obtained from different substances, such as hair, wool, and muscular fibre, 

 appeared in some cases more, and in others less viscid, though similar in every other property. It will 

 be proper also to observe, that the saponaceous solutions were always filtrated, before the addition of 

 the acids. f The yolk of eggs, when boiled with caustic lixivium of potash, forms a pale olive- 

 coloured concrete animal soap, which, when dissolved in water, and saturated with muriatic acid, is 

 precipitated in the state of mere fat. Yolk of egg, by incineration, affords a small portion of phosphate 

 of soda and of lime. 



VOL. XVIII. 5 B 



