1895.] Fluorine as a Test for the Fossilization of Animal Bones. 317 
ter of the bones has not been examined, but the reader is rec- 
ommended to an interesting study upon that subject by Mons. 
Scheurer-Kestner in the Bulletin de la Societe chimique, 1870, 
Vol. I, page 199, and Vol. II, page 11. 
As for the mineral substances of these bones, the differ- 
ence is sometimes small, but other times large from the initial 
composition. The proportion of carbonate of lime is generally 
increased, although in a measure extremely variable. The 
amount of phosphate of lime has frequently diminished, 
whether by reason of solution and infiltration of water or by the 
formation of phosphate of iron. The magnesia is found in pro- 
portion nearly identical to those which existin the bones of liv- 
ing animals. The boneshave always retained a notable quantity 
of iron, whether in the state of hydrate of peroxide which col- 
ors them a reddish-brown, or in the state of phosphate of per- 
oxide, rarely in the state of ferrous phosphate. The reducing 
actions have sometimes determined the deposit of sulphide of 
iron under the form of pyrites inattackable by hydrochloric 
acid. This has taken place notably in the vertebra of the 
ichthyosaurus from the Kimmeridgian clays of Havre. There 
is sometimes found in these bones, a certain quantity of sul- 
phate of lime. The calcination with organic matter could 
give rise to the sulphur. The bones contain frequently a 
small quantity of clay or of silica in the form of quartz. They 
are also, though rarely, almost entirely transformed into crys- 
talline or crystallized quartz; such is the case with the speci- 
men from the trias at Bayreuth. 
The chlorine is almost always in slight proportion in the 
fossil bones as well as in the modern, especially if one 
has taken care to eliminate by washing the soluble chlor- 
ides, and to leave only the chloride of calcium combined with 
the phosphate of lime. Fluorine is found always in a greater 
and more important quantity corresponding to several hun- 
dredths of fluoride of calcium. This salt forms with the phos- 
phate of lime a nearly insoluble compound comparable to ap- 
atite; it appears to augment, in a certain measure, with the 
antiquity of the bones, so that one is able, up to a certain 
point, to find in the relative proportion of phosphoric acid and 
of fluorine, an index to the degree of fossilization. 
12 (To be continued.) 
