SIR H. DAYV S AGRICULTURAL CHEMISTRY; 



151 



ot marine plants, are very valuable in common in the vegetable kingdom than 

 commerce, principally on account of their I magnesia, and magnesia more common 



uses in the manufacture of glass and 

 soap. Glass is made from fixed alkali, 

 flint, and certain metallic substances. 



To know whether a vegetable yields 

 alkali, it should be burnt, and the ashes 

 washed with a small quantity of water. 

 If the water, after being for some time ex- 

 posed to the air, reddens paper, tinged 

 ^vith turmeric, or renders vegetable blues 

 green, it contains alkali. 



To ascertain the relative quantities of 

 pot-ashes afforded by different plants, 

 equal weights of them should be burnt ; 

 the ashes washed in twice their volume 

 of ^vater ; the washings should be ])assed 

 through blotting paper, and evaporated to 

 dryness ; the relative weights of the salt 

 obtained, will indicate very nearly the 

 relative quantities of alkali they contain. 

 The value of marine plants in produc- 

 ing soda, may be estimated in the same 

 manner with sufficient correctness for 

 commercial purposes. 



Herbs, in general, furnish four or five 

 times, and shrubs two or three times as 

 much pot-ashes as trees. The leaves pro- 

 duce more than the branches, and the 

 branches more than the trunk. Vegeta- 

 bles burnt in a green state produce more 

 ashes than in a dry state. The following 

 table* contains a statement of the quan- 

 tity of pot-ashes afforded by some com- 

 mon trees and plants. 

 10,000 parts of Oak - - - 15 



of Elm - - - 39 



of Beach - - 12 



of Vine - - - 55 



of Poplar - - 7 



of Thistle - - 53 

 of Fern - - - 62 

 of Cow Thistle - 196 

 of Worm Wood - 7.30 

 of Vetches - - 275 

 of Beans - - 200 



of Fumitory - - 790 

 The earths found in plants are four ; 

 silica, or the earth of flints, alumina, or 

 pure clay, lime and magnesia. They are 

 procured by incineration. The lime is 

 usually combined with carbonic acid. 

 This substance and silica are much more 



• It is founded upon the experiments of Kirwaji, 

 Vauqulin, and Pertuis. 



than alumina. Tiie earths form a prin- 

 cipal part of the matter insoluble in 

 water, afforded by the ashes of plants. 

 The silica is known by not being dis- 

 solved by acids ; the calcareous earth, 

 unless the ashes have been very intensely 

 ignited, dissolves with effervescence in 

 muriatic acid. JNIagnesia forms a soluble 

 and crystallizable salt, and lime a diffi- 

 cultly soluble one with sulphuric acid. 



Alumina is distinguished from the 

 other earths, by being acted upon very 

 slowly by acids; and in forming salts 

 very soluble in water and difficult of 

 crystallization with them. 



The earths appear to be compounds of 

 peculiar metals (mentioned page 94,) and 

 oxygen, one proportion of each. 



The earths afforded by plants are ap- 

 plied to no uses of common life ; and 

 there ai'e few cases in which the know- 

 ledge of their nature can be of impor- 

 tance, or afford interest to the farmer. 



The only metalic oxides found in 

 plants are those of iron and manganesum: 

 they are detected in the ashes of plants, 

 but in very minute quantities only. 

 When the ashes of plants are reddish 

 brown they abound in oxides of iron. 

 When black or purple in oxide of man- 

 ganesum ; when these colors are mixed 

 they contain both substances. 



The saline compounds contained in 

 plants, or afforded by their incineration, 

 are very various. 



The sulphuric acid combined with po- 

 tassa, or sulphate of potassa, is one of the 

 most usual. Common salt is likewise 

 very often found in tlie ashes of plants, 

 likewise phosphate of lime, which is in- 

 soluble in water but soluble in muriatic 

 acid. Compounds of nitric, muriatic, 

 sulphuric, and phosphoric acids with al- 

 kalies and earths exist in the sap of many 

 plants or are afforded by their evapora- 

 tion and incineration. The salts of po- 

 tassa are distinguished from those of soda, 

 by their producing a precipitate in solu- 

 tions of platina ; those of lime are cha- 

 racterized by the cloudiness they occa- 

 sion in solutions containing oxalic acid , 

 those of magnesia, by being rendered 

 cloudy by solutions of ammonia. Sul- 



