Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
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The Acid
Acts In This Instance As The Oxygen Of The Atmosphere At A Temperature
From 27 To 35 Degrees; For The White Coagulum Grows Yellow In Two Or
Three Minutes, When Exposed To The Sun.
After a few hours the yellow
colour turns to brown, no doubt because the carbon is set more free
Progressively as the hydrogen, with which it was combined, is burnt.
The coagulum formed by the acid becomes viscous, and acquires that
smell of wax which I have observed in treating muscular flesh and
mushrooms (morels) with nitric acid. According to the fine experiments
of Mr. Hatchett, the albumen may be supposed to pass partly to the
state of gelatine. The coagulum of the papaw-tree, when newly
prepared, being thrown into water, softens, dissolves in part, and
gives a yellowish tint to the fluid. The milk, placed in contact with
water only, forms also membranes. In an instant a tremulous jelly is
precipitated, resembling starch. This phenomenon is particularly
striking if the water employed be heated to 40 or 60 degrees. The
jelly condenses in proportion as more water is poured upon it. It
preserves a long time its whiteness, only growing yellow by the
contact of a few drops of nitric acid. Guided by the experiments of
Fourcroy and Vauquelin on the juice of the hevea, I mixed a solution
of carbonate of soda with the milk of the papaw. No clot is formed,
even when pure water is poured on a mixture of the milk with the
alkaline solution.
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