1838] 



FARMKRS' REGISTER. 



669^ 



of other chemists, offer simple explanations of 

 several processes in nature and art, by which dif- 

 ferent vetretablc substances are converted into 

 6ach other, or changed into new compounds. 



Gum and sugar, excluding the different propor- 

 tions of water they may contain, afford nearly the 

 same elements by analysis; and starch differs 

 from them only in containing a little more carbon. 

 The peculiar properties of gum and sugar must 

 depend chiefly upon the difi'erent arrangement, or 

 degree of condensation of their elements; and it 

 would be natural to coticeive, from the composi- 

 tion of these bodies, as well as that of starch, that 

 all three would be easily convertible one into the 

 other; which is actually the case. 



At the time of the ripening of corn, the sac- 

 charine matter in the grain, and that carried from 

 the sap vessels into the grain, become coagulated, 

 probably simply by losing water, and form starch. 

 And in the process of malting, the converse 

 change occurs. The starch of grain is converted 

 into sugar. As there is a little absorption of oxy- 

 gen, and a formation of carbonic acid in this case, 

 h is likely that the starch loses a little carbon, 

 which combines wiih the oxygen to form carbonic 

 acid; and probably the oxygen tends to acidify 

 the gluten of the grain, and thus breaks down 

 the texture of the starch; gives a new arrangement 

 to its elements, and renders it soluble in water. 



Mr. Cruikshank, by exposing syrup to a sub- 

 stance named phosphuret of lime, which has great 

 tendency to decompose water, converted a part of 

 the susrar into a matter analogous to mucilage. 

 And M. KirchhofT, recently, has converted starch 

 into sugar by a very simple process, that of 

 boiling in very diluted sulphuric acid.* The pro- 

 portions are 100 parts of starch, 400 parts of 

 Water, and 1 part of ihe sulphuric acid by weight. 

 This mixture is to be kept boiling for 40 hours ; 

 the loss of water by evaporation being supplied by 

 new quantities. The acid is to be neutralized by 

 fime ; and the sugar crystallized by coolincr. This 

 experiment has been tried with success by many 

 persons. Sir C. Tuthill, from a pound and a half 

 of potato starch, procured a pound and a quarter 

 of crystalline, brown sugar; which he conceives 

 possessed properties intermediate between Cane- 

 sugar, and grape-sugar. 



It is probable, from the experiments of M. 

 Theodore de Sauszure, that conversion of starch 

 into sugar, in this experiment, is effected merely 

 by its combination with water; lor his experiments 

 prove that the acid is not decomposed, and that no 

 elastic matter is set free, and that the sugar 

 weighs more than the starch from which it is 

 formed: probably the color of the sugar, is owing 

 to the disengagement or new combination of a little 

 carbon, the slight excess of which, as has been just 

 stated, constitutes the only difference (independent 

 of the different quantities of water tliey may 

 contain) perceptible by analysis between sugar and 

 starch. 



M. Bouillon la Grange, by slishtly roasting 

 fiiafch, has rendered it soluble in cold water ; and 



* Some kinds of vinegar, especially tfiose made from 

 sugar, are converted into an insoluble substance re- 

 sembling lignin, or the principle of the woody fibre, 

 by exposure to the atmosphere. This I have witness- 

 ed in many instances; the new substance which is like 

 lignin. forms on the ?urface of the vinegar, and leaves 

 Vol. VI.-77 



the solution evaporated afforded a substance, 

 having the characters of mucdage. And by ex- 

 periments similar to those of M. Kirchhoff', M. 

 Braconnot has lately shown that saccharine and 

 mucilaginous substances may be procured from 

 various forms of woody fibre; and I have seen 

 specimens of soft sugar made from linen rags. 



Gluten and albumen differ from the other ve- 

 getable products, principally by containing azote. 

 When gluten is kept long in water, it undergoes 

 fermentation ; ammonia (which contains its azote) 

 is given off with acetic acid ; and a fiitty matter 

 and a substance analogous to woody fibre remain. 



Extract, tannin, and gallic acid, when their 

 solutions are long exposed to air, deposite a matter 

 similar to woody fibre ; and the solid substances 

 are rendered analogous to woody fibre, by slight 

 roasting; and in tfiese cases it is prot^able that 

 part of their oxygen and hydrogen is separated as 

 water. 



All the other vegetable principles differ from the 

 vegetable acids in containing more hydrogen and 

 carbon, or less oxygen ; many of them, therefore, 

 are easily converted into vegetable acids by a mere 

 subtraction of some proportions of hydrogen. 

 The vegetable acidr^, for the most part, are con- 

 vertible into each other by easy processes. The 

 oxalic contains most oxygen; the acetic the least: 

 and this last substance is easily formed by the dis- 

 tillation of other vegetable substances, or by the 

 action of the atmosphere on such of them as are 

 soluble in water; probably by the mere com- 

 bination of oxygen with hydrogen and carbon, or 

 in some cases by the subtraction of a portion of 

 hydrogen. 



Alcohol, or spirits of wine, has been often men- 

 tioned in the course of these lectures. This sub- 

 stance was not described amongst the vegetable 

 principles, because it has never been found ready 

 formed in the organs of plants. It is procured by 

 a change in the principles of saccharine matter, in 

 a process called vinous fermentation. 



The expressed juice of the grape contains sugar, 

 mucilage, gluten, and some saline matter, princi- 

 pally composed of tartaric acid: when this juice, 

 or must, as it is commonly called, is exposed to 

 the temperature of about 70^^, the fermentation 

 begins; it becomes thick and turbid; its tempera- 

 ture increases, and carbonic acid gas is disengaged 

 in abundance. In a few days the fermentation 

 ceases; the solid matter that rendered the juice 

 turbid falls to the bottom, and it clears; the sweet 

 taste of the ffuid is in great measure destroyed, 

 and it is become spirituous. 



Fabroni has shown that the gluten in must is 

 essential to fermentation ; and that chemist has 

 made saccharine matter ferment, by adding to its 

 solution in water, common vegetable gluten and 

 tartaric acid. Gay Lussac has demonstrated that 

 must will not ferment when freed froiri air by boil- 

 ing, and placed out of the contact of oxygen ; but 

 that fermentation begins as soon as it is exposed 

 to the oxygen of air, a little of that principle be- 

 ing absorbed ; and that it then continues inde- 

 pendent of the presence of the atmosphere.* 



a dense strong crust, occasionally in appearance not un- 

 like the huffy coat of blood. — J. D. 



* Farther experiments appear to be required on (his 

 subject. I have not found the fermentation of must 

 prevented either by immnrsing in it phosphorus in a 

 close vessel, or by agitating it, in contact with a mi- 

 nute portion of nitrous gas. — J. D. 



