148 



SCIENCE OF GARDENING. 



Paut il. 



water ; and if the solution is exposed to the action of the atmosphere, the water is gradually evaporated, 

 and the gum again left in a solid mass. According to the analysis of Gay Lussac and Thcnard, it consists 

 of the following elements, in the following proportions, 100 parts being the integer: carbon ■i2-23; oxy- 

 gen oOS-i; hydrogen 6-93 ; saline and ear*hy matter a small quantity; total 100. Gum tragacanth is 

 the produce of the astragalus tragacantha, a thorny shrub that grows in the islands of the Levant. It is 

 less transparent than gum arable, and not so easily dissolved in water. Cherry-tree gum is obtained 

 from the prunus avium, and other species of the same genus, and in general from all trees with stone- 

 fruit, from which it exudes spontaneously and in great abundance. It differs" from gum arabic and tra- 

 gacanth in its concreting in larger masses, and being more easily melted. Mucilage is found chiefly in 

 the roots and leaves of plants, particularly such as are bulbous and succulent ; the bulbs of the hyacinth 

 and leaves of the marshmallow. It is found also in iiax-seed, and in many of the lichens, and is to be 

 obtained only by maceration in water, from which it is separated by means of sulphuric acid. 



The uses of gum are considerable. In all its varieties it is capable of being used as an article of food, 

 and is highly nutritive, though not very palatable. It is also employed in the arts, particularly in calico- 

 printing, in which the printer makes choice of it to give consistency to his colors, and to prevent them 

 from spreading. The botanist often uses it to fix his specimens upon paper, for which purpose it is very 

 weU adapted. It forms likewise an ingredient in ink ; and in medicine it forms the basis of many mix- 

 tures, in which its influence is sedative and emollient. 



642. Sugar is the produce of the sr.ccharum otRcinarum. [Jig. 53.) 53 

 The canes or stems of the plant, when ripe, are bruised between the - .n, 



rollers of a mill, and the expressed juice is collected and put into large ui;,li. 

 boilers, in which it is mi.xed with a small quantity of quicklime, or 

 strong ley of ashes, to neutralise its acid, and is then made to boil. 

 The scum which gathers on the top during the process of boiling is 

 carefully cleared away ; and when the juice has been boiled down to 

 the consistence of a S3'rup, it is drawn oifand allowed to cool in vessels 

 which are placed above a cistern, and perforated with small holes, 

 through which the impure and liquid part, known by the name of mo- 

 lasses, escapes ; while the remaining part is converted into a mass of 

 small and hard granules of a brownish or whitish color, known by the 

 designation of raw sugar, which, when imported into Europe, is further 

 purified by an additional process, and converted by filtration or crystal- 

 lisation into what is called loaf sugar, or refined sugar, or candied 

 sugar. Sugar thus obtained has a sweet and luscious taste, but is 

 without smell. According to.Dr. Thomson its specific caloric is 1-0S6, its 

 specific gravity 1-40-15; and its constituent elements are oxygen 64-7; 

 carbon 27 '5; hydrogen 7 '8 ; total 100". The juice of the acor sacchari. 

 num, or American maple, yields sugar in such considerable abundance 

 as to make it an object v/ith the North American farmer to manufac- 

 ture it for his own use. A hole is bored in the trunk of the vegetating 

 tree eai-ly in the spring, for the purpose of extracting the sap; of 

 which a tree of ordinary size, that is, of from two to three feet in dia- 

 meter, will yield from one hundred and fifty to two hundred pints and upwards, in a good season. The 

 sap, when thus obtained and neutralised by lime, deposits, by evaporation, crystals of sugar in the pro. 

 portion of about a pound of sugar to forty pints of sap. It is not materially different in its properties 

 from that of the sugar-cane. The juice of the grape, when ripe, yielcts also a sugar by evaporation and 

 the action of pot-ashes, which is known by the appellation of the sugar of grapes, and has been lately 

 employed in France as a substitute for colonial sugar, though it is not so sweet or agreeable to the taste. 

 The root of beta vulgaris, or common beet, yields also, by boiling and evaporation, a sugar which is dis- 

 tinguished by a peculiar and slightly bitter taste, owing perhaps to the presence of a bitter extractive 

 matter which has been found to be one of the constituents of the beet, ^ugar has been extracted from 

 the following vegetables also, or from their productions : from the sap of the birch, sycamore, bamboo, 

 maize, parsnep, cow-parsnep, American aloe, dulse, walnut-tree, and cocoa-nut-tree; from the fruit of 

 the common arbutus, and other sweet-tasted fruits ; from the roots of the turnip, carrot, and parsley ; 

 from the flower of the euxine rhododendron ; and from the nectary of most other flowers. 



643. Tne utility of suga?; as an aliment is well known ; and it is as much relished by many animals as 

 by man. By bees it is sipped from the flowers of plants, under the modification of nectar, and converted 

 into honey ; and also seems to be relished by many insects, even in its concrete state ; as it is also by many 

 birds. By man it is now regarded as being altogether indispensable, and though used chiefly to give a 

 relish or seasoning to food, is itself highly nutritive. It is also of much utility in medicine, and cele- 

 brated for its anodyne and antiseptic qualities, as well as thought to be peculiarly etficacious in preventing 

 diseases by worms. 



644. Starch. If a quantity of wheaten flower is made into a paste with v/ater, and kneaded and 

 washed under the action of a jet, till the water runs off colorless, part of it will be found to have been 

 taken up and to be still held in suspension by the water, which wiU, by-and-by, deposit a sediment that 

 may be separated by decantation. This sediment is starch, which maybe obtained also immediately from 

 the grain itself, by means of a process well known to the manufacturer, who renders it finally fit for the 

 market by washing and edulcorating it with water, and afterwards drying it by a moderate heat. Starch, 

 when thrown upon red-hot iron, burns with a kind of explosion, and leaves scarcely any residuum behind. 

 It has been found by the analysis of Gay Lussac and Thenard, to be composed of carbon 43-53 ; oxygen 

 49"G8 ; hydrogen 6-77 ; total 100'. This result is not very widely different from that of the analysis of 

 sugar, into which, it seems, starch may be converted by diminishing the proportion of its carbon, and 

 increasing that of its oxygen and hydrogen. This change is exemplified in the case of the malting of 

 barley, which contains a great proportion of starch, and which absorbs during the process a quantity of 

 oxygen, and evolves a quantity of carbonic acid ; and accordingly part of it is converted into sugar. 

 Perhaps it is exemplified also in the case of the freezing of potatoes, which acquire in consequence a sweet 

 and sugary taste, and are known to contain a great deal of starch, which may be obtained as follows : let 

 the potatoes be taken and grated down to a pulp, and the pulp placed upon a fine sieve, and water made 

 to pass through it : the water will be found to have carried off with it an infinite number of particles, 

 which it will afterwards deposit in the fonn of a fine powder, separable by decantation ; which powder is 

 starch, possessing all the essential properties of wheaten starch. It may be obtained from the pith of 

 several species of palms growing in the Moluccas and several other East Indian islands, by the following 

 process : the stem, being first cut into pieces of five or six feet in length, is split longitudinally so as to 

 expose the pith, which is now taken out and pounded, and mixed with cold water, which after being 

 well stirred up, deposits at length a sediment that is separated by decantation, and is the starch which 

 the pith contained, or the sago of the shops. 



645. Salop is also a species of starch that is prepared, in the countries of the East, from the root of the 

 orchis morio, mascula, bifolia, and pyramidalis, and in the isle of Portland, from the arum maculatum. 

 So also is cassava, which is prepared from the root of jatropha manihot, a native of America, the ex- 

 pressed juice of which is a deadly poison, used by the Indians to poison their arrows ; but the sediment 

 which it deposits is a starch that is manufactured into bread, retaining nothing of the deleterious property 

 of the juice ; and so also is sowans, which is prepared from the husk of oats, as obtained m the process 

 of grinding. 



