556 
APPENDIX. 
introduced with the food, or created out of it, (it being yet a 
problem to solve how this and other elementary matters are pro- 
duced,) it can be readily conceived why compounds with it and 
lime should be formed as well as with the former acid ; because, as 
the earthy and other matters are absorbed from the moisture of 
the soil, they must necessarily meet with these acids when they 
exist, and the vitality of the plant does not prevent their forming 
the crystals which have been here described ; still there are some 
curious points connected with their production. If oxalic or phos- 
phoric acid be added to a solution of lime, instead of crystals, a 
pulverulent opaque precipitate is obtained, which does not happen 
in the interior of the plants : therefore various experiments have 
been devised, to discover the method of making crystals by 
combining the above substances. Some have been ineffectual, 
such as making a plant, which contains lime in its composi- 
tion, absorb water with a small quantity of oxalate of ammonia 
dissolved in it : from the want of temperature which would create 
a necessity for moisture in the plant this experiment failed. A 
method, however, which succeeded was, to connect a vessel con- 
taining a solution of oxalate of ammonia with one containing 
lime water, by means of a few fibres of cotton : this gradual 
introduction of one fluid to the other formed perfect crystals of 
oxalate of lime on the ends of the fibres which were in contact 
with the lime water. This having succeeded, another attempt was 
made to form them in the interior of the cells of such plants as did 
not previously possess them : some difficulty occurred in finding any 
one fitted for the purpose, and at last Rice-paper, as it is termed, (the 
concentric slice from the pith of ^schynomene and Hibiscus,) 
was selected as the best material for the experiment, from its 
admitting an examination of their formation, by becoming trans- 
parent when charged with fluid. 
This substance was placed in lime water under an air pump, and 
the cells were soon filled with that fluid ; it was then dried and sub- 
mitted two or three times to the same process : by this means the 
cells were well charged with lime. Portions of this substance were 
placed in weak solutions of oxalic and phosphoric acids, and allowed 
to remain. On the third day, when examined, the cells in both 
instances contained much precipitate, together with numerous 
crystals ; those in the oxalic acid being precisely like the conglo- 
merate form in Rhubarb, and those in the phosphoric being rhom- 
bohedra, but none of the acicular shape were found, even after 
continuing the process beyond eight or ten days. 
