On the Erythric Acid, ec: 4\ 
effervescence which takes place when dilute sulphuric acid is 
poured on it. 
‘17. Dissolving the erythrat of lime in an excess of acid, a trans- 
parent, tasteless fluid is obtained. The oxalic acid discovers 
the lime, but to that carbonic acid must not be added; the al- 
kaline carbonats however immediately render it turbid. Alco- 
hol produces a similar effect, but it appears that it separates the 
nentral erythrat. The acidulous salt slowly evaporated yields 
crystals, in which the acids produce no effervescence whatever. 
The solution of these crystals dees not become turbid with lime- 
water, and it has lost all the characters of the original salt. It 
being necessary to examine the changes which occur in erythric 
acid when united to bases, we must leave for the present the in- 
vestigation of this phenomenon. 
18. A drop of erythric acid produces a copious precipitate in 
barytic water. This erythrat presents phenomena analogous to 
those before observed in erythrats of lime. The erythric acid 
decomposes rapidly the sulphuret of barytes, and yields a violet 
colour. 
Erythrats of Potash and of Soda. 
19. Caustic potash immersed in the erythric liquid produces 
no precipitate, nor any remarkable change of colour; but their 
combination has a very sweet taste. The erythrat of potash 
renders lime-water turbid, and precipitates some metallic solu- 
tions, such as that of lead and silver, in white coagulated matter 5 
on the contrary, with others it forms soluble coloured compounds, 
among which are distinguished the products from the solutions 
of iron by their beautiful blue colours. 
20. The erythrat of potash changes its nature very easily. In 
fact, on examining it some time after it was formed, it was found 
that from being neutral, or even somewhat alkaline, it had be- 
come acidulous, as was indicated by turnsole; nor would it yield 
a blue colour with the salts of iron, unless some drops of potash 
were newly added. 
21. The same and perhaps still more rapid changes take 
place, if the neutral erythrat be exposed to the light of the sun. 
In this state it is generally seen to become yellowish, and after- 
wards to redden. Removed from the solar light, and after a time, 
it loses the colour it had aé¢quired ; but if it remains exposed to 
that light it finally becomes a solid mass, sweet, of a lively red, 
and possessing much tenacity; dissolved iu water, it gives to the 
liquid its beautiful colour. This red liquor does not so easily 
Jose its colour by the action of the fire, as happens when it has 
no potash; but for this effect it is necessary to add much water, 
22. The action of a moderate fire accelerates the above effects, 
the red hue appearing and becoming still deeper. ‘Towards the 
. conclusion 
