Book I. VEGETABLE CHEMISTRY. 32^ 



highly inflammable metal, which he denominates potassium, and oxygen one proportion of each. Sod.'; 

 is found chiefly in marine plants, from the ashes of which it is obtained by means of lixiviation. It exists> 

 in great abundance in salsola soda, zostera maritima, and in various species of fuci. It is generally ob- 

 tained in the state of a carbonate, but is purified in the same manner as potass, to which it is similar in its 

 properties ; but from which it is easily distinguished by its forming a hard soap with oil, while potass forms 

 a soft soap. It consists, according to Sir H. Davy, of one proportion of a metal which he denominates 

 sodium, and two proportions of oxygen. Such are the only vegetable alkalies, and modes of obtaining 

 them. They are found generally in the state of carbonates, sulphates, or muriates, salts that form beyonrf 

 all comparison the most abundant ingredient in the ashes of green herbaceous plants whose parts are in a 

 state of vegetation. The ashes of the golden rod, growing in an uncultivated soil, and of the bean, turn- 

 sol, and wheat, were found by Saussure to contain at least three "fourths of their weight of alkaline salts. 

 This was nearly the case also with the leaves of trees just bursting from the bud. But the proportion of 

 alkaline salts is found to diminish rather than to augment as the parts of the plant are developed. 

 The ashes of the leaves of the oak, gathered in May, yielded 47 parts in the 100 of alkaline salts ; and in 

 September, only 17. 



14'75. The utility of the alkalies, as obtained from vegetables, is of the utmost importance in the arts, 

 particularly in the formation of glass and of soaps. If a mixture of soda or potass, and silex or sand, in 

 certain proportions, is exixjsed to a violent heat, the ingredients are melted down into a fluid mass, which 

 is glass in a state of fusion. In this state it may be moulded into almost any form at the pleasure of the 

 artist. And accordingly we find that it is manufactured into a great variety of utensils and instruments, 

 under the heads of flint-glass, crown-glass, bottle-glass. Bottle-glass is the coarsest ; it is formed of soda 

 and common sand, and is used in the manufacture of the coarser sort of bottles. Crown-glass is composed 

 of soda and fine sand: it is moulded into large plates for the purpose of forming window-glasses and 

 looking-glasses. Flint-glass is the finest and most transparent of all : that which is of the best quahty is 

 composed of 120 parts of white siliceous sand, 40 parts of pearl-ash, "^ of red oxide of lead, 13 of nitrate of 

 potass, and 25 of black oxide of manganese. It is known alSo by tlie name of crystal, and may be cut and 

 polished so as to serve for a variety of ornamental purposes, as well as for the more important and more 

 useful purposes of forming optical instruments, of which the discoveries of the telescope and the micro- 

 scope are the curious or sublime results. If a quantity of oil is mixed with half its weight of a strong 

 solution of soda or potass, a combination takes place which is rendered more complete by means of boiling. 

 The new compound is soap. The union of oil with potass forms soft soap, and with soda hard soap ; sub- 

 stances of the greatest efficacy as detergents, and of the greatest utility in the washing and bleaching of 

 linen. The alkalies are used also in medicine, and found to be peculiarly eflicacious in the reduction of 

 urinary calculL 



1476. Earths. The only earths which have hitherto been found in plants are the 

 following : lime, silica, magnesia, alumina. 



1477. Litne is by far the most abundant earth. It is generally combined with a portion of phosphoric, 

 carbonic, or sulphuric acid, forming phosjihates, or carbonates, or sulphates of lime. The phosphate of 

 lime is, next to the alkaline salt, the most abundant ingredient in the ashes of green herbaceous plants, 

 whose parts are all in a state of vegetation. The leaf of a tree, bursting from the bud, contains in its ashes 

 a greater proportion of earthy phosphate than at any other period : 100 parts of the ashes of the leaves of 

 the oak, gathered in May, furnished 24 parts of earthy phosphate ; in September, only 18-25, In annual 

 plants the proportion of earthy phosphate diminishes from the period of their germination to that of their 

 flowering. Plants of the bean, before flowering, gave 145 parts of earthy phosphate ; in flower, only 13-5. 

 Carbonate of lime is, next to phosphate of lime, the most abundant of the earthy salts that are found in 

 vegetables. But if the leaves of plants are washed in water the proportion of carbonate is augmented. 

 This is owing to the subtraction of their alkaline salts and phosphates in a greater proportion tlian their 

 lime. In green herbaceous plants, %vhose parts are in a state of increase, there is but little carbonate of 

 lime; but the ashes of the bark of trees contain an enormous quantity of carbonate of lime, and much 

 more than the alburnum, as do also the ashes of the wood. The ashes of most seeds contain no carbonate 

 of lime ; but they abound in phosphate of potass. Hence the ashes of plants, at the period of the maturity 

 of the fruit, yield less carbonate of lime than at any previous periotl 



1478. Silica is not found to exist in a great proportion in the ashes of vegetables, unless they have been 

 previously deprived of their salts and phosphates by washing; but when the plants are washed in water, 

 the proportion of their silica augments. The ashes of the leaves of the hazel, gathered in May, yielded 

 25 parts of silica in 100. The same leaves, washed, yielded four parts in 100. Young plants, and leaves 

 bursting from the bud, contain but little of silica in their ashes ; but the proportion of silica augments as 

 the parts are developed. But perhaps this is owing to the diminution of the alkaline salts. The ashes of 

 some stalks of wheat gathered a month before the time of flowering, and having some of the radicle leaves 

 withered, contained 12 parts of silica and 65 of alkaline salts in 1(X). At tlie period of their flowering, and 

 when more of their leaves were withered, the ashes contained 32 parts of silica and 54 of alkaline salts . 

 Seeds divested of their external covering, contain less silica than the stem furnished with its leaves ; and 

 it is somewhat remarkable that there are trees of which the bark, alburnum, and wood, contain scarcely 

 any silica, and the leaves a great deal, particularly in autumn. This is a phenomenon that seems inexpli- 

 cable. The greater part of the grasses contain a very considerableproportion of silica, as do also the plants 

 of the genus equisetum. Sir H. Davy has discovered that it forms a part of the epidermis of these plants, 

 and in some of them the principal part. From KX) parts of the epidermis of the following plants the pro- 

 portions of silica were, in bonnet cane, 90 ; bamboo, 714 ; common reed, 48-1 ; stalks of corn, &i-5. Owing 

 to the silica contained in the epidermis, the plants in which it is found, are sometimes used to give a polish 

 to the surface of substances where smoothness is required. The Dutch rush, equisetum hyemale, a plant 

 of this kind, is used to polish even brass. 



1479. Magnesia does not exist so abundantly in the vegetable kmgdom as the two preceding earths. It 

 has been found, however, in several of the marine plants, particularly the fuci ; but salsola soda contains 

 more of magnesia than any other plant yet examined. According to Vauquelin, 100 parts of it contain 

 17 929-'of magnesia. 



1480. Alumina has been detected in several plants, but never except m very small quantities. 



1481. Metallic oxides. Among the substances found in the ashes of vegetables, we must class also metals. 

 They occur, however, only in small quantities, and are not to be detected except by the most delicate ex- 

 periments. Tlic metals hitherto discovered in plants are iron, manganese, and perhaps gold. Of these 

 iron is by far the most common. It occurs in the state of an oxide, and the ashes of hard and woody plants, 

 such as the oak, are said to contain nearly one twelfth of their own weight of this oxide. The aslies of 

 salsola contain also a considerable quantity. The oxide of manganese was first detected in the ashes of 

 vegetables by Scheele, and afterwards found by Proust in the ashes of the pine, calendula, vine, green oak, 

 and fig-tree. Beccher, Kunckel, and Sage, together with some other chemists, contend also for the ex- 

 istence of gold in the ashes of certain plants ; but the very minute portion which they found, seems more 

 likely to have proceeded from the lead employed in the process than from the aslies of the plant. It has 

 been observed by Saussure, that the proportion of the oxides of iron and of manganese augments in the 

 ashes of plants as their vegetation advances. The leaves of trees furnish more of these principles in au- 

 tumn than in spring. It is so also with annual plants. Seeds contain metals in less abundance than the stem ; 

 and if plants are washed in water, the proportions of their metallic oxides is augmented. 



1482. Such are the principal ingredients that enter into the vegetable composition. They are indeed 

 numerous, though some of them, sucii as the metallic oxides, occur in such small proportions as to render 



