VEGETABLE PRODUCTS. 



155 



f^lr1li^lled twenty-four parts of earthy piiospliato, 

 in September only eighteen parts. In annual 

 plants the proyortion of earthy ])hosphate di- 

 minishes from the period of their gcnnination 

 to that of their flowering. Plants of the bean, 

 before flowering, gave fourteen parts of earthy 

 lihosphate ; in flower only thirteen. Carbonate 

 of lime is, next to phospliate of lime, the most 

 abundant of tlie earthy salts that are found in 

 vegetables ; but if the leaves of plants are washed 

 in water, the proportion of carbonate is aug- 

 mented. This is owing to the subtraction of 

 their alkaline salts and phosphates in a greater 

 proportion than their lime. In green herbace- 

 ous plants, whose parts are in a state of increase, 

 there is but little carbonate of lime; but the 

 ashes of the bark of trees contain an enonnous 

 quantity of this earth, 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 period. 



Silica, or flint earth, is not found to exist in 

 great proportion in the ashes of vegetables, un- 

 less 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 2i parts 

 of silica in the hundred ; the same leaves washed 

 yielded 4 parts in the hundred. Young plants 

 and leaves bursting from the bud contain but 

 little silica in their ashes; but the proportion of 

 silica augments as the parts are developed. This 

 is perhaps owing to the diminution of the alka- 

 line salts. The ashes of some stalks of wheat, 

 gathered a month before the time of flowering, 

 and having some of the radical leaves withered, 

 contained 12 per cent, of silica, and 05 of alka- 

 line Sidts. At the period of their flowering, and 

 when more of their leaves were withered, the 

 allies contained .•52 parts of silica, and 5-i of alka- 

 line salts. Seeds, divested of their external cov- 

 ering, contain less silica than the stem furnished 

 with its leaves; and it is somewhat remarkaljle 

 that there are trees of which the bark, alburiuim, 

 and wood, contain scarcely any silica, and the 

 leaves a great deal, particularly In autumn. This 

 IS a phenomenon that cannot be readily accounted 

 for. The greater part of the grasses contain a 

 very considerable proportion of silica, as do also 

 the plants of tho genus cquisctum. Sir II. Davy 

 discovered that it forms a part of the epidermis 

 of these plants, and in some of them the prin- 

 cipal ]>art. From 100 parts of the epidermis of 

 the following plants, the proportions of silica 

 were as follows : 



Bonnet cine, 

 li.inibtjo. 



no. 



71.4 



Cnnmion reed, 

 Stiilks of corn, 



4R.1 

 C0'.5 



Owing to the silica contained in the cpidcnnis, 

 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, 

 a j)lant of this kind, is used to polish even brass. 

 Alumina. This earth exists in the ashes of 

 several plants, but not by any means so gene- 

 rally, or in such proportions, as lime, or even 

 silica. Saussure found in the ashes of the com- 

 mon fir ] 4 per cent, of alumina. In many other 

 plants, however, only a trace of it is discoverable. 

 Yet clay earth forms a large, and apparently an 

 indispensidile ingredient, in all soils adapted for 

 the support of vegetables. 



Magnesia. This earth is also sparingly found 

 in vegetables. It is confined chiefly to marine 

 species, as the fuci. Vauquelin obtained 17 per 

 cent, of magnesia from the ashes of sahola soda. 

 Metallic oxides. Some of the metals exist in 

 minute proportions in the ashes of vegetables, 

 such as gold, magnesia, and iron. The latter 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 part their weight of this oxide. The 

 ashes of salsola contain also a considerable quan- 

 tity. The oxide of magnesia was first detected 

 in vegetables by Scheele, and afterwards found 

 by Proust in the ashes of the pine, vine, green 

 oak, and fig tree. It has been stated, too, that 

 minute portions of gold have been detected in 

 vegetable bodies. Saussure remarks that the 

 properties of the oxides of iron and of magnesia 

 augment in the ashes of plants as their vegeta- 

 tion advances. The leaves of trees furnish more 

 of these prineijdes in autumn than in spring. It 

 is so also with annual plants. Seeds contain 

 metals in less abundance than the stem ; and if 

 plants are washed with water, the proportion of 

 their metallic oxides is augmented. 



JDccomjyosilion of vegctahlcs. During the spon- 

 taneous decomposition which all vegetables, in 

 common with all organized bodies, undei-go, it is 

 obvious that the simi)le substances of which they 

 are composed must unite together in a different 

 manner from that in which they were formerly 

 united, and fonn a new set of compounds which 

 did not fonnerly exist. Now it has been re- 

 marked, that the specific gravity of these new- 

 compounds is almost always loss than that of 

 the old body. Some of them usually fly oft' in 

 the state of gas or vapour ; hence the odour that 

 vegetable bodies emit during the whole time that 

 they are running through the series of their 

 changes. When the odour is very off'ensive or 

 noxious, the spontaneous decomposition is called 

 putrefaction ; but when the odour is not offen- 

 sive, or w-hen any of the new comjjounds formed 

 is a])plied to useful purposes, the spontaneous 



