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The production of an optogram on the retina by the photochemical action of light on the visual purple; the fixation of an image in the eye. The object so photographed shows white on a purple or red background. See Visual purple, under Visual.

e substance in which the mineral salts are deposited to form bone; -- called also ostein. Chemically it is the same as collagen.

he fat of animal tissues, with olein and butyrin in butter, with olein in olive oil, etc. Chemically, it is a glyceride of palmitic acid, three molecules of palmitic acid being united to one molecule of glyceryl, and hence it is technically called tripalmitin, or glyceryl tripalmitate.

an illuminant and lubricant. It is very inert, not being acted upon by most of the strong chemical reagents. It was formerly regarded as a definite compound, but is now known to be a complex mixture of several higher hydrocarbons of the methane or marsh-gas series; hence, by extension, any substance, whether solid, liq…

seudomorph, in which there has been a change of physical characters without alteration of chemical composition, as the change of aragonite to calcite.

pecies to another, so as to involve a change in physical characters without alteration of chemical composition.

The quality or condition of any substance which has no inclination to chemical activity; inactivity.

The department of science which is concerned with the mineralogical and chemical composition of rocks, and with their classification: lithology.

A chemical laboratory. [Obs.] Dunglison.

A generalization with regard to systems of chemical equilibrium, discovered by Prof. J. Willard Gibbs. It may be stated thus: The degree of variableness (number of degrees of freedom) of a system is equal to the number of components minus the number of phases, plus two. Thus, if the components be salt and water, and th…

The hypothetical principle of fire, or inflammability, regarded by Stahl as a chemical element.

translucent waxy substance, having a characteristic disagreeable smell. It is very active chemically, must be preserved under water, and unites with oxygen even at ordinary temperatures, giving a faint glow, -- whence its name. It always occurs compined, usually in phosphates, as in the mineral apatite, in bones, etc.…

The branch of chemistry which relates to the effect of light in producing chemical changes, as in photography.

process of etching on copper, steel, or zinc, by means of the action of light and certain chemicals, so that from the plate impressions may be taken. Sir D. Brewster.

o`to*graph"ic*al*ly, adv. Photographic printing, the process of obtaining pictures, as on chemically prepared paper, from photographic negatives, by exposure to light.

r material organization; cognizable by the senses; external; as, the physical, opposed to chemical, characters of a mineral.

ever in the theory that the fundamental phenomena of life are to be explained upon purely chemical and physical principles; -- opposed to vitalist.

The important living portion of protoplasm, considered a chemical substance of the highest elaboration. Germ plasm and idioplasm are forms of plasmogen.

with gold, silver, or other metals, either by a mechanical process, as hammering, or by a chemical process, as electrotyping.

ductile and malleable, but very infusible, and characterized by its resistance to strong chemical reagents. It is used for crucibles, for stills for sulphuric acid, rarely for coin, and in the form of foil and wire for many purposes. Specific gravity 21.5. Atomic weight 194.3. Symbol Pt. Formerly called platina. Plati…