418 
DR. YELLOLY ON THE TENDENCY 
Lithate of ammonia, oxalate of lime, lithate of ammonia, and lithic 
acid 1 
phosphate of lime, oxalate of lime, and lithate of ammonia . 1 
Oxalate of lime, lithic acid, lithate of ammonia, and lithic acid . . 1 
lithic acid, oxalate of lime, and phosphate of lime .... 1 
lithic acid, oxalate of lime, and mixed phosphates .... 1 
lithic acid, lithate of ammonia, and mixed phosphates ... 1 
663 
The general results of the annexed Table, differ in no very material respect 
from those mentioned in my former paper. The great preponderance of calculi 
of lithic acid, and lithate of ammonia, or of their nuclei ; and the usual 
presence of carbonate of lime, with phosphate of lime, and the mixed phos- 
phates, are prominent characteristics of the whole cabinet. But it will be seen, 
with interest, that silex enters into the composition of one specimen ; and as 
this is a point of great rarity, I shall state to the Society the circumstances 
under which it exhibited itself, and the mode by which its existence has been 
ascertained. — In examining a dark brown calculus of oxalate of lime, of about 
five grs. in weight, which was removed many years since from a boy of nine 
years of age, I found some minute, colourless, transparent crystals, diffused 
irregularly in the substance of the dark oxalate, which, from their great hardness, 
and their insensibility to all the usual reagents, I suspected to be siliceous. 
The specimen was however so small, as to make it important to establish its 
nature by one set of experiments only; and I therefore, in my first subsequent 
visit to London, in February last, requested a valuable member of this Society, 
Mr. Faraday of the Royal Institution, to examine it with me ; which he obli- 
gingly did ; and the following is an account of the experiments which he 
employed. 
A portion of the calculus being separated, which contained about nine of 
these granules, the oxalate of lime, and whatever other substance might be in 
combination with it, was destroyed by heat, and afterwards by muriatic acid. 
The granules were then left transparent and colourless ; capable of scratching 
glass and agate, and unaffected by nitric or muriatic acids. These granules 
were then dried and exposed to heat, with a fused mixture of carbonate of 
