ACIDS. Generally sharp, sour substanc.es, which redden litmus paper, and combine with metallic oxides or bases to form salts.. All acids, however, are not sour to the taste, since all oily bodies contain one or more acids, and corn starch sugar is made by means of sulphuric acid. The inorganic acids are mineral ones. Those of inter est in agriculture are, sulphuric, muriatic, silicic and phosphoric acids. Sulphuric acid is a com ponent of gypsum, forming with the base sul phate of lime. Muriatic acid occurs in salt, as chloride of hydrogen, forming chloride of soda (common salt). Silicic acid occurs in quartz, or rock crystal (which forms so considerable a por tion of the earth's surface, and so large a portion of many sands), and is essentially silicic acid, be ing a compound of oxygen with a base, forming silicon. Phosphoric acid is contained in the bones of animals and man, in combination with lime, being a salt of phosphoric acid. Phos phites, again, are salts of phosphorous acid, con taining less oxygen than phosphoric acid. The highest degree of oxygenation is marked in chemistry by the termination ie, and the salt thus formed terminates in ate. Thus we have carbonate of lime from carbonic acid and a base. The termination ous, signifies a lower degree of oxygenation, and its compound terminates in ite. A still lower degree of oxygenation is termed hypo. Thus, in compounds of nitrogen we have nitric acid, nitrous acid, and hypo-nitrous acid; the, last containing the least oxygen, and the first the most. The important vegetable acids are, nitric, acetic, carbonic, tannic, gallic, prus sic, humic, oxalic, tartaric, benzoic, citric and inalic acid. Nitric acid in a pure state is un known ; the strongest contains one atom of acid to two of water, and, in this state, is extremely caustic, dissolving most metals. The pure acid would consist of one atom of nitrogen with five of oxygen. Acetic acid is formed in vinegar by the second fermentation of wine, cider or beer ; the first being the vinous fermentation. Acetic acid is also a product of the combustion of wood, containing no resin, as in making charcoal, combined with empyrcumatic oils. When freed from these, it is called pyroligneous acid. Acetic acid, in its most concentrated state, is extremely sour, acrid and pungent. The combinations of acetic acid with various bases are termed acetates; thus we have the acetate of lead, copper, iron and alumina. Carbonic acid is formed of one atom of carbon and two of oxygen. The air contains from four to six parts in 10,000. Soils containing vegetable matter give it off during decay. From carbonic acid plants obtain their supply of carbon in the shape of starch, sugar, vegetable fiber, etc. Carbonic acids in plants is decomposed in the light, and a part of its oxygen is thrown out by the leaves, thus giving this im portant element back to the air from whence it came. Tannic or gallic acid is a white astrin
gent powder. with acid reaction. Tannin is the astringent principle of galls, sumac, catechu, oak, hemlock, and other barks. Their value for tanning is reckoned according to the quantity of tannic acid they contain. The following table, from Davy, shows the amount of tannic acid contained in various substances.
Oak bark . . .. 29 Lombardy poplar. 15 Spanish chestnut .. 21 Birch .
Leicester willow (large) 33 Hazel.. ... 14 Elm .... 13 Blackthorn ..... . . . 16 Common willow (large). 11 Coppice oak.... .... 32 Ash 16 Inner rind of oak bark 72 Beach 10 Oak cut in autuinn . 21 Horse chestnut. 9 Larch cut in autumn .
Sy c am ore 11 Sicilian sumac contains about 78 parts in 480 parts. Nut galls 127 parts, and catechu 261 parts in 480. Prussic acid is a pellucid fluid of strong odor, and is contained in numerous plants of the rosa ceous family, especially in the almond and peach, from the seeds and blossoms of which it is distilled. It is composed of one equivalent of cyanogen and one of hydrogen. It is one of the most deadly poisons known. Cyanogen is a gas which burns with a blue flame. With oxygen it forms cyanic acid. The gas is poisonous, and forms cyanides by combining with various met als. Humic acid contains carbon 64, hydrogen 4, and oxygen 32 parts in 100. By treating the humus of the soil (black humus) with carbonate of soda, by boiling a dilute solution of carbonate of soda and humus tog,ether, a dark brown liquid is obtained, which owes its color to the ulmate of soda contained. By repeating the process with the humus, and with fresh quantities of the liq uid carbonate, the fluid at last remains clear. Ulmic acid has passed into the solution, and ulmin remains undissolved in the residue mixed with earth, sand, and the other component parts of the humus or peat. Humic acid may also be obtained by the action of strong hydrochloric acid, of sulphuric acid, and of alkalies upon su gar and other substances containing cellulose. Oxalic acid is found in its free state in the hairs of the chick pea (cicer uric, innm). In combina tion with potash it is found in rhubarb, sor rels and docks, and in combination with lime in lichens. When pure, it is a very soluble crystal line, colorless, solid, intensely sour, and fatally poisonous. Benzoic acid gives aroma, to many balsams, and sweet-scented grasses and other plants. Citric acid is the sour principle of cher ries, cranberries, gooseberries, lemons and other fruits. Malic acid- is the acid principle of apples, pears, plums, etc. Tartaric acid, combined with potash, is contained in the juice of the grape, in tamarinds, bilberries, etc. As food ihe acids are not of value. They are, however, grateful to most palates. They are cooling, and are said to furnish carbon in some degree in respiration.