104 On the Acids contained in the [Fex. 
juices: amongst the rest, that of the rhubard plant occupied my 
attention. 
Mr. Henderson has lately examined this juice ; and he announces 
that he has discovered in it a new and peculiar acid, which he calls 
the rheumic. 
There are some facts with which I am acquainted, and some 
objections to the conclusions drawn by that gentleman, that seemed 
necessary to be considered before the rheumic acid can be admitted 
as a distinct substance. These I shall, therefore, state. 
In my experiments I found the predominant acid in the stalks of 
thubarb to be malic, but there was also a quantity of the sorbie 
present. No other acid manifested itself ; but as I was not inves- 
tigating with the design of discovering a new one in the plant, I do 
not pretend to say that it contained no other. 
Of the presence of these acids, Mr. Henderson does not appear 
to have been aware ; but he found reason to suppose that citric acid 
is one of the component parts of the juice. When, therefore, he 
saturated the acid juice with lime, he obtained malate, sorbate, and 
citrate of lime, all of which are insoluble salts: and when this 
powder was acted on by sulphuric acid, the result was a mixture of 
sorbic, malic, and citric acids. 
When the juice was saturated with chalk, a supermalate of lime 
was formed; but this being soluble, it might have been washed 
away during the edulcoration of the precipitate. 
Beside the acids naturally contained in the juice, there are others 
introduced by the process. ‘The mixed salts of lime, already no- 
ticed, were decomposed by sulphuric acid, which, as during the 
subsequent evaporation, it charred the vegetable portion, must have 
been in excess. Hence sulphuric acid, along with those already 
mentioned, would adulterate the product. During the charring, a 
quantity of acetic acid must also have been produced. 
By employing the other method proposed by Mr. Henderson of 
combining the acid juice with lead, and acting on the compound 
with nitric acid, we give origin to new impurities, such as nitric, 
oxalic, and perhaps other vegetable acids. 
Thus in the resulting fluid obtained by the proposed processes 
there may be malic, sorbic, citric,* sulphuric, acetic, nitric, and 
oxalic acids. And from the great solubility of the crystals supposed 
to be rheumic acid, it appears that they could not be formed unless 
in a highly concentrated solution. Hence recrystallization would 
not entirely exclude the adulterating acids; and some of them 
would even be present in the solid form. 
Several salts formed during this process would still further in- 
quinate the substance supposed to be the pure acid. ‘Thus malate, 
sorbate, citrate, and sulphate of lime, are soluble in the acids 
* I have no other grounds for supposing the presence of citric acid than the 
experiment stated by Mr. Henderson. 
