SIR H. DAVY S AGRICULTURAL CHEMISTRY. 



149 



crab, and not from a degenerated apple, 

 for the former will possess much of the 

 hardiness, and vigor, while the latter 

 will generally inherit all the disease of 

 the parent tree. The autumn is named 

 as the best time for planting. 



Observations on Fermentation, hy 

 M. Gay Lussac. — Spirituous fermenta- 

 tion is the result of mutual action of 

 saccharine mucilage and of a peculiar 

 ferment approaching in its chemical com- 

 position very nearly to animal matter. 



If the nature of the mixture and the 

 temperature be suitable, fermentation 

 may both begin and proceed without 

 the concurence of any other substance, 

 especially of oxygen gas. 



Animal and vegetable substances may 

 be preserved from fermentation or de- 

 composition by enclosing them in air 

 tight glass vessels, and subjecting them 

 for some hours to the heat of boiling 

 water. 



Three open vessels filled with cow's 

 milk, with currant juice, and with a solu- 

 tion of gelatine in water, were scalded by 

 immersion in boiling brine at first 

 twice a day, and afterwards once a day, 

 for the space of two months. The currant 

 juice and jelly remained unchanged; the 

 cream of the milk was converted into 

 hard butter, and the milk itself was rather 

 thinner than at first. Malt in close ves- 

 sels may be made to ferment by adding 

 carbonic acid. — Jinn, de Chim. 



SIR H. DAVY S AGRICULTURAL CHEMISTRY. 

 (Continued from p. 141.) 



All of theseacids, except the acetic, ma- 

 lic, and the prussic acids, are white crystal- 

 lized bodies. The acetic, malic, and 

 prussic acids have been obtained only in 

 the fluid ; they are all more or less solu- 

 ble in water ; all have a sour taste except 

 the gallic and prussic acids ; of which 

 the first has an astringent taste, and the 

 latter a taste like that of bitter almonds. 

 The oxalic acid exists uncombined, in 

 the liquor which exudes from the chick 

 pea (Cicer arietinum) and may be pro- 

 cured from the wood sorrel ( Oxalis ace- 

 tosella,) common sorrel, and other spe- 

 cies of Rumex ; and from the Geranium 

 acidum. Oxalic acid is easily discover- 



ed and distinguished from other acids by 

 its property of decomposing all calcare- 

 ous salts, and forming with lime a salt in- 

 soluble in water ; and by its crystallizing 

 in four sided prisms. 



The citric acid is a peculiar acid exist- 

 ing in the juice of lemons and oranges. 

 It may likewise be obtained from the 

 cranberry, whortleberry, and hip. 



Citric acid is distinguished by its form- 

 ing a salt insoluble in water with lime ; 

 but decomposable by the mineral acids. 



The tartaric acid may be obtained 

 from the juice of mulberries and grapes ; 

 and likewise from the pulp of the tama- 

 rind. It is characterized by its property 

 of forming a diificultly soluble salt with 

 potassa, and an insoluble salt decomposa- 

 ble by the mineral acids with lime. 



Benzoic acid may be procured from 

 several resinous substances by distilla- 

 tion ; from benzoin, storax and balsam of 

 Tolu. It is distinguished from the other 

 acids by its aromatic odour, and by its 

 extreme volatility. 



Malic acid may be obtained from tlie 

 juice of apples, barberries, plums, elder- 

 berries, currants, strawberries, and rasp- 

 berries. It forms a soluble salt with 

 lime ; and is easily distinguished by this 

 test from the acids already named. 



Acetic acid, or vinegar, may be obtain- 

 ed from the sap of different trees. It is 

 distinguished from malic acid by its pe- 

 culiar odour ; and from the other vegeta- 

 ble acids by forming soluble salts with 

 the alkalies and earths. 



Gallic acid may be obtained by gently 

 and gradually heating powdered gall nuts, 

 and receiving the volatile matter in a 

 cool vessel. A number of white crys- 

 tals will appear, which are distinguished 

 by their property of rendering solutions 

 of iron deep purple. 



The vegetable prussic acid is procured 

 by distilling laurel leaves, or the kernels 

 of the peach and cherry, or bitter al- 

 monds. It is characterized by its pro- 

 perty of forming a bluish green precipi- 

 tate, when a little alkali is added to it, 

 and it is poured into solutions containing 

 iron. It is very analogous in its proper- 

 ties to the prussic acid obtained from 

 animal substances ; or by passing ammo- 

 nia over heated charcoal ; but this last, 



