108 (Ml KM 



30 to 40 per cent, of sugar. He extracted it by satu- 

 rating the acids contained in the juice of grape* 

 potash, boiling it down to one half, and setting it aside. 

 Several of the salts subsided. The juice was then mixed 

 with blood, heated, scummed, filtered, and boiled down 

 to syrup. Crystals of raw sugar gradually form, which 

 may be purified by repeating tiic process. This sugar 

 i white, but inferior in consistence to common sugar. 

 It is not so sweet, and resembles sugar from honey. 

 Like it, the sugar of grapes crystallizes in sphericles. 

 It is less soluble than common sugar, and does not go 

 so far in sweetening liquids. 



Sugar was first extracted from the beet by MargrafF. 

 Many experiments were afterwards made upon the ex- 

 traction, by Achard and other German philosophers, 

 and attempts made to substitute the sugar of beet for 

 common sugar, but it could not be obtained at a low 

 enough price. It has a greater resemblance to common 

 sugar than the sugar of grapes ; but is distinguished by 

 a certain nauseous bitter taste, owing perhaps to the pre- 

 sence of some foreign substance. 



Manna is the produce of various trees, but is chiefly 

 obtained from the fraxinns ornus, a species of ash, which 

 grows abundantly in Sicily and Calabria. It partly ex- 

 udes spontaneously during the summer months, and is 

 partly obtained by incisions. The juice gradually con- 

 cretes into a solid mass, or it is dried in the sun, or in 

 stoves. Pure manna is very light, and appears to con- 

 sist of a congeries of fine capillary crystals. Its taste is 

 sweet, and it leaves a nauseous impression in the mouth. 

 Hot alcohol dissolves it readily, and, on cooling, depo- 

 sitcs about 5-8ths of the manna in the state of a fine light 

 spongy crystalline mass, bearing some resemblance to 

 camphor. This deposite may be considered as pure 

 manna. It has an agreeable sweet taste, and instantly 

 melts on the tongue, like snow in warm water. When 

 dissolved in nitric acid, it yields oxalic acid. The sac- 

 lactic appears also when the manna is impure. Manna 

 does not undergo the vinous fermentation, and seems in 

 consequence incapable of furnishing alcohol. Manna it- 

 self seems to be formed from uncrystallizable sugar by a 

 species of fermentation. 



The plants yielding sugar are very numerous. It sel- 

 dom exudes spontaneously from vegetables, though this 

 is sometimes the case. 



SECT. III. Of Sarcocoll. 



--rcocoll. 'rhit substance, which has hitherto been confounded 

 with the gum resins, though its properties are very dif- 

 ferent, exudes spontaneously from the pcnata sarcocolla, 

 a shrub said by botanical writers to be indigenous in the 

 north-eastern parts of Africa. It may be obtained pure 

 by solution in alcohol, filtration, and evaporation. 



. Pun- sarcocoll has a brown colour, is semitransparent, 



:propcr- j i i T T 



,j e , and very like gum in appearance. Its speciGc gravity is 



1.2684. 



It has a sweet taste, but leaves an impression of bit- 

 terness. It dissolves readily both in water and alcohol. 

 The solution is yellow. It does not crystallize. When 

 heated, it softens, but does not melt. It emits a slight 

 smell of caromel. When strongly heated it blackens, 

 and assumes the consistence of tar, emitting a heavy 

 white smoke, having an acrid odour. Nitric acid dis- 

 solves it, but does not convert it into tannin. From 

 these properties, sarcocoll appears to be intermediate be- 

 tween gum and sugar. 



Y. 



SECT. IV. Of .Ispnragin. , ian ,, r 



\V,- .Mve this name to a substance discovered in the i_^ T ij 

 juice of atparagus, by Vauquelin and Robiquct. The A|>arjj ; n 

 juice was evaporated to the consistence of a syrup, and 

 set aside. Crystal* of asparagin formed in it spontane- 

 ously. 



These crystals are white and transparent, and have It; proper- 

 the figure of rhomboidal prisms. The greater angle of "" 

 the rhomboidal base is 130". 



Asparagin is hard and brittle. Its taste is cool, and 

 slightly nauseous, so as to occasion a secretion of saliva. 



It dissolves readily in hot water, but in cold water on- 

 ly sparingly. Alcohol does not dissolve it. 



The aqueous solution does not affect vegetable blues. 

 Neither infusion of nutgalls, acetate of lead, oxalate of 

 ammonia, muriate of barytes, nor hydrosulphuret of pot- 

 ash, occasion any change in it. When triturated with 

 potash, no ammonia is disengaged. The potash seems 

 to render it more soluble in water. 



When heated it swells, and emits penetrating vapours, 

 affecting the eyes and nose, like the smoke of wood. It 

 leaves a large portion of insipid charcoal, which, when 

 incinerated, gives scarcely a trace of residue. 



Nitric acid dissolves it with the evolution of nitrous 

 gas. The solution has a yellow colour, and a bitter 

 taste, like that of animal substances in the same acid. 

 Lime disengages from it a considerable quantity of am- 

 monia. 



SECT. V. Of Gum. 



There is a thick transparent tasteless fluid, which Gum. 

 sometimes exudes from certain species of trees. It is 

 very adhesive, and gradually hardens without losing its 

 transparency, but easily softens again when moistened 

 with water. This exudation is known by the name of 

 gum. The gum most commonly used is that which 

 exudes from different species of the mimosa, particularly 

 the nilolica, and is known by the name of gum urtibic. 



Gum is usually obtained in small pieces like tears, How ob- 

 moderately hard, and somewhat brittle while cold, so taincd. 

 that it can be reduced by pounding to a fine powder. 

 When pure it is colourless ; but it has commonly a yel- 

 lowish tir/ge, and it is not destitute of lustre. It has no 

 smell. Its taste is insipid. Its specific gravity varies 

 from 1.3161 to 1.4817. 



It is not altered by exposure to the air, but the light Its proper- 

 of the sun makes it assume a white colour. Water dis- tics, 

 solves it in large quantities. The solution, which is 

 known by the name of mucilage, is thick and adhesive. 

 It is often used as a paste, and to give stiffness and lustre 

 to linen. When evaporated, the gum is obtained unal- 

 tered. Mucilage may be kept for years without under- 

 going putrefaction : at last, however, the odour of ace- 

 tic acid becomes perceptible in it. 



When gum is exposed to heat, it softens and swells, 

 but does not melt ; it emits air bubbles, blackens, and 

 at last, when nearly reduced to charcoal, emits a low 

 blue flame. A white ash remains, consisting chiefly of 

 the carbonates of lime and potash. 



Gum does not appear to be acted upon by oxygen gas, 

 simple combustibles, azote, or the metals. The only 

 metallic salts which occasion a precipitate when dropt 

 into mucilage, arc nitrate of mercury, and acetate of lead, 

 both of which occasion a white precipitate. The super- 

 acetate of lead occasions no change. When oxymuriatc 



