88 



CHEMISTRY. 



and by the destructive distillation of wood. Various fermented liquids 

 when exposed to the air become sour, that is, their alcohol unites 

 with the oxygen of the air, giving rise to vinegar. The formula for 

 alcohol is C*H^O-f HO. If to this we add four atoms of oxygen, 

 we have Q'W'O'^^-^O, which gives the formula of hydrated acetic 

 acid, = C^H^O^ HO-f 2H0. 



The vinegar of commerce is chiefly made from wine or cider. 

 The acid from wood is procured by distilling hard wood in close ves- 

 sels ; acetic acid is found among the products which come over ; 

 this requires redistillation and some subsequent treatment. This 

 variety is termed pyrolig7ieous acid. 



The strongest acetic acid is prepared by distilling anhydrous ace- 

 tate of soda with concentrated oil of vitriol. Crystals of hydrate of 

 acetic acid are formed, which may be drained from the more fluid 

 portion. At the temperature of 63° these crystals fuse into a limpid 

 liquid, of a density of 1-063, possessing the pungent smell and taste 

 of vinegar, and capable of blistering the skin. It is soluble to any 

 extent in water and alcohol. Its vapour is inflammable. The 

 water, which is essential to the constitution of acetic acid, is basic^ 

 and can only be replaced by some metallic oxide ; anhydrous acetic 

 acid, in a separate state, is unknown. 



The acetates are all soluble salts ; those of silver and mercury 

 are least so. The most important acetates are the acetate and sub- 

 acetate of lead, acetate of ammonia, (spirit of Mindererus,) and acetate 

 of copper (verdegris). 



Acetone, or pyroacet.ic spirit, is a volatile, colourless liquid, which 

 is produced when any of the metallic acetates are subjected to a de- 

 structive distillation. It has a density of 792°, and boils at 132°; it 

 is very inflammable, burning with a bright flame. 



Citric acid, C^ H^ 0,,-f 3H0.— This acid is found in the fruits 

 of the genus citrus, including the lemon, sour orange, citron, and 

 lime; also in several others, in combination with malic acid. It 

 may be procured by saturating lemon juice with chalk, and then de- 

 composing the citrate of lime by means of sulphuric acid. The citric 

 acid crystallizes on evaporation. It forms colourless prismatic crys- 

 tals, very soluble in water, of a very sour taste. The three atoms 

 of water which it contains are essential to its constitution. 



Malic acid, CJ^fi^Jr'^liO, derives its name from the apple, in 

 which fruit it largely exists. It may be procured by saturating apple 

 juice with lime, and decomposing the malate of lime by sulphuric 

 acid. It is a deliquescent acid, without colour, and an acid taste. 

 It is bibasic. 



Lactic acid, C6H305-fHO, derives its name from the word lac, the 

 Latin for milk. It is the acid which exists in sour milk. It has 

 lately been shown to be the product of a peculiar fermentation called 

 viscous, by which the sugar of milk is converted into lactic acid. It 



