84 CHEMICAL CONSTITUTION OF VEGETABLES. 



various manufacturing processes ; still it si.ould not be confeunded 

 with gum in a chemical point of view. The acids act with more or 

 less energy on starch, and give rise to different prod nets. Nitric 

 acid, when it is dilated with water, merely dissolves fecula ; but at 

 a certain degree of concentration it exerts a destructive action. Id 

 this reaction several acids are formed, among others oxalic acid 

 By employing very dilute sulphuric acid, Kirchhoff succeeded iL 

 changing starch into a saccharine substance similar to the sugar of 

 the grape. The operation may be performed in a leaden or silvei 

 pan, or, what is preferable, especially when the process is carried 

 on upon the great scale, in wooden vessels, in which the liquid mass 

 is heated by steam. According to M. Couverchel, several organic 

 acids are capable of changing fecula into sugar in a similar manner ; 

 such are oxalic, tartaric, and malic acids. 



The artificial conversion of starch into grape-sugar has not yel 

 been satisfactorily accounted for. The acid employed does not seero 

 to undergo any change ; it is found in its original state and quantity 

 after the operation. M. de Saussure thinks that the eflect of the 

 reaction is the fixation of water ; thus 100 parts of fecula yielded 

 him 110.40 parts of sugar.* 



M. Couverchel and M. Guerin, on the contrary, state that the 

 quantity of sugar obtained was less than, that of the starch they 

 employed. 



Gluten exerts a reaction on starch similar to that produced by 

 acids ; Kirchhoff discovered, that under the influence of the azotized 

 matters which are met with in flour, the fecula is converted into 

 sugar. t Two parts of starch being mixed with four parts of cold 

 water, on atlding twenty parts of boiling water, a thick paste is pro- 

 duced ; if into this one part of dry powdered gluten be introduced, 

 and the mixture be kept at the temperature of GO" cent. (140° Fahr.) 

 the paste becomes more and more liquid, so that the mixture may 

 be fdtered at the end of from six fo right hours. By concentration 

 a sirup is obtained, in which small crystals of sugar are perceived. 

 It is well known that during the act of germination, fermentable 

 saccharine matter is produced. Kirchhoff concluded, from his ex- 

 periments, that this production of sugar in genniiiation is attributa- 

 ble to the reaction of the gluten on the starch. Germmating grain, 

 barley-malt, for instance, reacts rapidlv^and powerfully on any fe- 

 cula with which it is brought into contact ; a fact well known to, 

 and constantly taken advantage of, by manutacturers of spirits from 

 potatoes and raw grain, largo mashes of which arc rapidly converted 

 into sweet fermentable iKjuids under the action of a little malt. 



These facts, it is evident, cannot be explained by Kirchhotrs ex- 

 periment ; in the fermentation of the potato, the mass of fecula to be 

 converted into sugar is too great com])are(l with the quantity of glu- 

 ten which exists in the malted barley. Further, the gluten in grain 

 which has not germinated, scarcely exerts any appreciable action. 



• 8au<«surr. Bihliothiijiic britanniciuc, t. Ivi. p. 333. 

 t Kirchhoff, Journii! do Phanimcie, I. ii. p. iVk 



