46 Improvements in Physical Science [Jan 
His experiments were made with great care; but his method is 
perhaps scarcely susceptible of the precision which is requisite in 
such delicate investigations. His numbers for gum arabic differ 
very much from those of Berzelius. The following are the results 
which he obtained. I have added the nearest atoms, neglecting the 
azote; because I am not quite satisfied respecting its presence in 
the substances subjected to analysis. ; 
COMPOSITION. 
Per Cent. In Atoms. 
Substances. Oxy. | Carbon. |Hydr. |A zot.| Oxy.|Carbon.| Hyd. 
Starch of wheat ......| 48°31 | 45°39 | 5°90 | O-4 4 5 1 
Starch Sugar.........- 55°87 | 37°29} 684) — 8 9 1 
Sugar of Grapes .....- 56°51 | 36°71 | 678 | — T 8 1 
Manna .....2..ec0ee- A43'80 | 47°82 | 6:06 | 0°32 8 13 1 
Gum-arabic .........- 48°26 | 45°84 | 5:46 | 0-44 | 4 5 1 
2. Conversion of Starch into Sugar.—The curious fact, first ascer- 
tained by Kirchoff, that starch when boiled in very diluted sul- 
phuric acid is converted into sugar, has lately engaged a good deal 
of the attention of chemists. Fourcroy takes notice that when 
starch is treated. with muriatic acid or chlorine it acquires a sweet 
taste. (General System of Chemical Knowledge, vol. viii. p. 157. 
English Trans.) Einhoff, in his elaborate analysis of the potatoe 
(Gehlen’s Journal, vol. iv. p. 445) showed that the mucilaginous 
matter of that root could be converted into a saccharine matter. 
His process was complicated ; but one part of it consisted in digest- 
ing the substance with acetic acid. This probably produced the 
effect. Nasse has shown that the starch extracted from raw potatoes 
is easily converted into sugar ; but that if the potatoe be boiled, or 
subjected to fermentation, the starch obtained from it is not con- 
vertible into saccharine matter: hence he concludes, that starch 
only from living vegetable matter is susceptible of this change, 
while the starch extracted from dead vegetable matter is incapable 
of it. But this conclusion seems a little too general. When 
potatoes are exposed to frost they become soft and sweet, and com- 
pletely lose the property of vegetating; they are, therefore, re- 
duced to dead vegetable matter. But the starch extracted from 
them in this state is perfectly similar to that from fresh potatoes. 
I have no doubt, therefore, that it might be converted into sugar 
by the usual process, though I have never had an opportunity of 
making the experiment. Nasse has shown that the opinions enter- 
tained by Fourcroy respecting the saccharine fermentation are 
erroneous, and that during the conversion of mucilaginous matter 
into sugar no fermentation whatever takes place. 
Vogel of Paris has shown that when starch is converted into 
sugar by boiling it in diluted sulphuric acid, no gas whatever is 
