730 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



and the water, which had acquired a brownish colour, was but little affected, even 

 by nitro-muriate of tin, which however formed a white cloud*. 



From some previous circumstances, which need not here be mentioned, I was 

 lastly induced to make some similar experiments on albumen; and as that of the 

 blood is mixed with gelatin, and with the substance called fibrin by the chemists, 

 which in chemical properties appears to be the same as muscular fibre, and as it is 

 with some difficulty that the albumen can be exactly separated from these substances, 

 I preferred the albumen of eggs, as being pure and unmixed ; and, in order that 

 it might be brought into a state in some measure similar to the bodies lately ex- 

 amined, by which I mean simple inspissation, I dried it, after coagulation, in a 

 vessel which was heated to 212° of Fahrenheit, till it became perfectly hard, brittle, 

 yellow, and semi-transparent, like horn. The albumen, in this state, was digested 

 8 days in boiling distilled water, which was occasionally renewed, in proportion to 

 the evaporation. In a few hours after the commencement of the digestion, the 

 transparent horny pieces of albumen were softened, and became white and opaque, 

 exactly like albumen recently coagulated; but, after this, no further change was 

 observed. At the end of 8 days, the water in which the albumen had been 

 digested was examined, and was found exactly to resemble that afforded by quill, 

 nail, and tortoise-shell; for the transparency of it was not disturbed by the tanning 

 principle, though nitro-muriate of tin produced a faint white cloud -j~. As far 

 therefore as could be ascertained, by long digestion in boiling distilled water, and 

 by the effects of the re-agents, albumen was proved to be very similar to tortoise- 

 shell, and many of the other substances previously noticed; but the close re- 

 semblance, or rather indeed identity, of albumen with those bodies, will be placed 

 in a stronger light, by the enumeration and comparison of their other chemical 

 properties. As I have, in the former part of this paper, had occasion to mention 

 the gelatin obtained from the sponges and gorgonize, it is not necessary here to 

 repeat those remarks, neither is it requisite that I should enter into any minute 

 account concerning the experiments made on bladder, and some other membranes. 

 It may therefore suffice here to observe, that all these bodies afforded more or less 

 gelatin ; that when this was separated, the remaining substance ceased to be tough, 

 or elastic, and was easily torn, like wetted paper; and that when dry, the sponges, 

 and such membranes as bladder and cuticle, became very brittle, and were shrivel- 

 led and curled up, like withered leaves of plants. 



But, before speaking of the nature of the substance which thus remained, it 

 will be proper, concisely to notice the effects of acids on the bodies which afford 



* The crust which covers insects like the scorpion, appears in every respect to be similar to tortoise- 

 shell. f When infusion of oak-bark is added to recent liquid albumen, it immediately forms a 



precipitate) and nitro-muriate of tin does not produce an effect till some hours have elapsed. But 

 after coagulation the reverse takes place; for the water in which coagulated albumen has been long 

 boiled, becomes turbid by the addition of nitro-muriate of tin j and is not in any manner affected by 

 infusion of bark. — Orig. 



