ON NEUTRAL MIXTURE. 
193 
from observation, that when a lemon has been exposed in a 
dry situation, until the skin becomes partially dried, it 
affords a considerably larger portion of juice than it would 
have done in its recent state. Could this be proved by 
experiment, we should try it. It is said by some that the 
quantity of citric acid in lemon juice varies as much as from 
20 to 30 per cent. Whether or not they had particular refer- 
ence to the imported lemon juice we cannot say; but judging 
from the various reports of the manufacturing chemists, we 
should say they had. We have found by experiment that the 
recent juice also varies considerably in the quantity of acid it 
contains, and that it varies just in proportion as the fruit be- 
comes drier, until decomposition commences; and we may 
add, just in proportion as the mucilaginous and saccharine 
matter seems to decrease. To try this experiment, three sorts 
of lemons were selected. The first were fresh. To saturate 
an ounce of juice expressed from these it required 9ij. of the 
carbonate of potassa. The second had been rolled separately 
in paper, and kept in a dry situation for about a month, so 
that their original dimensions were considerably reduced, but 
they retained their natural colour, odour, &c. To saturate an 
ounce of the juice furnished by these, about 46 grains of the 
carbonate of potassa were necessary. The third were such as 
had by time and exposure become almost brown, and hard ex- 
ternally. An ounce of juice expressed from these, required 
50 grains of the carbonate of potassa to saturate it. Under 
such circumstances as those just related, the bicarbonate of 
potassa was used, and we found in the several instances from 
i to i more of it to be necessary. We have already suggested 
the propriety of using the bicarbonate instead of the regular 
carbonate of potassa for making the Neutral Mixture, but since 
experimenting we have thought it immaterial which was used. 
The object of using the bicarbonate instead of the regular car- 
bonate was to get rid of the precipitated silica, but as the 
mixture is opaque made with either, a preference would be 
useless. From what we have learned by experiment and 
otherwise, we are induced to think that in every instance it 
