18 PREPARATION AND MOUNTING 
6rH Drvision. \ 
The proper solvents of calcareous animal matters are 
nitric, hydrochloric, and sulphuric acids. The earth of 
bones consists of a combination of two tribasic phosphates 
of lime, both of which are entirely soluble in nitric and 
hydrochloric acids. Sulphuric acid abstracts a part of the 
lime of bones, leaving a superphosphate—a substance much 
used in agriculture as a manure. JF lnoride of calcium, 
existing in small quantity in bones, but in larger in the 
enamel of teeth (and of the ganoid scales of fish ?), is de- 
composed by sulphuric acid, which combines with the cal- 
cium, allowing the hydrofluoric acid to fly off in a gaseous 
state. Carbonate of lime dissolves in nitric and hydro- 
chloric acids. The shells of mollusca, and testz of echino- 
dermata, consisting principally of carbonate of lime, are also 
soluble in the same acids, as well as those of nummulites 
foraminifera, &c., which have been infiltrated with siliceous 
matter. These present the most beautiful “ casts,” which 
are exactly of the shape of the Sarcode body and canal sys- 
tem, thus enabling their internal organs to be studied with 
much accuracy. Dr. Carpenter says that they are of “ won- 
derful completeness.” - 
7TH DIvIsION. 
Silica is nearly altogether insoluble in water, but dissolves 
freely in strong alkaline solutions. Its only acid solvent is 
hydrofluoric acid, Its combinations with a larger proportion 
of alkali are soluble in water, and from such solutions silica 
may be precipitated in a gelatinous or colloid form by 
acids, or separated by dialysis, in the form of colloid silica. 
This substance may be used for procuring certain modifica- 
tions of crystals of salts for the polariscope, such as.sulphate 
of magnesia, sulphate of copper, boracic acid, sulphate of zinc, 
&c. In its combination with a smaller proportion of alkali, 
forming glass, it is attacked by hydrofluoric acid and its 
vapour, and advantage may be taken of this property te 
