1820.] Physical Science during the Year 1819. 87 



But how can we reconcile the great discordance between Mar- 

 cet and Gay-Lussac in the weights of common salt and of 

 muriate of magnesia ? 



XII, Vegetable Substances. 



, 1. Starch. — It has been long known to chemists that when 

 starch is exposed to heat till its colour begins to change and to 

 become yellow, its properties are so far altered that it is now 

 soluble in cold water, and forms a viscid, brown-coloured solu- 

 tion, which may be substituted for an aqueous solution of starch, 

 M. Lassaigne has made some experiments to determine whether 

 starch by this roasting process is converted into gum. 



When the aqueous solution of roasted starch is evaporated to 

 dryness, it leaves a brownish-yellow viscid matter. Boiling 

 alcohol, when digested on this matter, acquires a fawn colour, 

 and when evaporated to dryness leaves a brownish-yellow matter, 

 having a bitter taste similar to that which several vegetable 

 bodies acquire when burnt ; but the greater part of the residue 

 was not acted upon by the alcohol. This portion being dissolved 

 in water, and the solution evaporated to dryness in a moderate 

 heat, left thin transparent plates, of a reddish-yellow colour, very 

 similar to the gum which flows from certain trees at the period 

 that they ripen their fruit ; but when this apparently gummy 

 matter was treated with nitric acid, it yielded oxalic acid without 

 any trace of saclactic acid. Hence it is obvious that it was not 

 in reality gum. (Jour, de Pharm. v, 300.) 



' In the Philosophical Transactions for 1819, there is inserted 

 a paper by M. Theodore de Saussure giving the result of a set 

 of experiments upon the spontaneous decomposition of a mix- 

 ture of starch and water, when left to itself, either in vacuo, or 

 with the access of air. A portion of the starch disappears 

 amounting to little less than one-fourth, and the remaining 

 three-fourths were converted into the following substances ; 



Sugar, 



Gum, 



Amylin, 



Starchy llgnin, 



Lignin mixed with charcoal. 



Starch ur.decomposed. 



The sugar possessed the characters of starch sugar, and 

 amounted to nearly half the weight of the starch. 



The gum possessed nearly the characters of the matter into 

 which starch is changed by roasting. We see from Lassaigne 's 

 experiments, given above, that it differs essentially from gum in 

 its properties. 



The ami/line (called amidiiie by Saussure) is a substance inter- 

 mediate between gum and starch. It is obtained from the 



