BASE AND BASIC. In chemistry, that element of a compound which most resembles hydrogen, and is most unlike oxygen in its chemical and electro-chemical relations, is called the base, and in substances composed of two simpler compounds, that compound which is like hydrogen is still the base, In electrolysis, the base travels to the cathode or negative metal, and is therefore called electro-positive ; while the acid or other body with which the base was combined, goes to the anode or positive pole, and is called electro-negative. The base travels in the direction of the electric current, and the acid agoind the current. The same relation appears to exist between these anions and eathions, in actino or photo-chemistry ; for bases are eminently favourable to actinic action, while acids are strongly opposed to it. Alkalis are very strongly basic, and exert a remarkable power as accelerators, while acids are strongly retardative. Of compounds in which the acid
and base completely neutralize each other, the action upon boclies undergoing actinolysis is neutral also ; henr,e nitrate of potassa may exists in the nitrate of silver solutions in considerable quantity, and yet give no indication of its presence. When a compound not neutral, contains both acid and base, it is said to be acid or basic according as the acid or basic element is in excess, and retards or accelerates as a pure acid or alkali would do. These facts have not been attended to sufficiently, and hence the discordant opinions of different photographers respecting the useful or injurious properties of the same substance. It should be carefully noted that every compound, whose effects are to be tried, is strictly neutral, or allow ances made for its want of neutrality.