42 On the Erythric Acid, Sc. 
conclusion of the evaporation, if the fire ceases to act, a very te- 
nacious sweet mass is obtained ; but if the fire be continued, an 
abundant red spume is produced. This spume dissolves rapidly 
in water, disengaging numerous bubbles, and communicating the 
usual red colour: in alcohol it is searcely soluble. 
23. That the erythrat of potash is subject to an almost im- 
mediate change, is confirmed even by another proof. Putting 
potash on the erystals of erythric acid, ‘they are dissolved; neutral 
erythrats are produced in ‘the state of a white powder, whieh if 
left in contact with the air spontaneously reddens. In water, with 
which however it has not much affinity, it furnishes a-solution 
which yields a blue colour with salts of iron; after some time it 
loses this property, and re-acquires it by means of the addition of 
fresh potash. But that which evidently demonstrates the change 
which take place, is the fact that, after ‘the lapse of several hours, 
the deposit which was before in a great measure insoluble in'wa- 
ter, becomes entirely dissolved if a small quanity of water be kept 
over it. This new solution requires the addition of potash to 
produce the blue colour with salts of iron. 
24. The same things are produced, if instead of caustic potash 
carbonat be used. The erythric acid has the power of develop- 
ing carbonic acid, and hence originates an alkaline erythrat, which 
like the others is subject to equal changes. Analogous pheno- 
mena are obtained with carbonat of soda; the erythrat of soda 
differs from that of potash in having a pungent taste, whereas 
the erythrat of potash i is sweet. 
25. From these it may be concluded, that erythric acid in 
contact with potash gives origin toa new acid endowed with a 
greater capacity of saturation, producing at the same time a pe- 
culiar matter which occasionally manifests itself with a red co- 
lour ; circumstances which lead to the suspicion that the new 
acid may be even more oxygenated than the erythric. Let us 
see if the action of alcohol gives greater importance to this con- 
jecture. 
26. The erythrat of potash is so much the less soluble in al- 
cohol the more it is aikaline.. Thus, if in aleohol which contains 
dissolved potash erythric acid be poured, an abundant precipitate 
appears, which is speedily dissolved by the addition of a little 
more erythric acid, and again reappears by adding fresh alcohol. 
This, therefore, does not alter the erythrat of potash in which 
the acid is in excess. The alcohol precipitating the erythrat 
deposits beautiful arborizations, which are formed of uniform 
shining crystals. These rapidly dissolve in water, and give it a 
sweetish taste. The solution is highly alkaline, does not preci- 
pitate lime-water, nor give a blue colour with solutions of iron ; 
jt acquires in no manner a red colour, aid contains, indeed, an 
, ; acid 
