13 PEEPA RATION AND MOUNTING 



CTH DIVISIOX. 



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. Fluoride 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 hy^ro- 

 chloric acids. The shells of mollusca, and tcstse of echino- 

 dermata, consisting principally of carbonate of lime, are also 

 soluble in the same acids, as well as those of nummulites, 

 forum inifera, &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." 



TTH 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 to 



