FLUORIDE OF CALCIUM IN WATER. 161 



slightly washed, etched quite distinctly. A still better process would be that 

 followed with the blood, where washing was reduced to a minimum. These expe- 

 riments throw no light on the condition in which fluorine exists in blood or milk ; 

 nor would it be easy to ascertain in what state of combination it occurs. In the 

 meanwhile we may suppose it to be present as fluoride of calcium. 



There is one other animal fluid, the last towards which suspicion as to its 

 containing fluorine was likely to have been entertained, in which hydrofluoric 

 acid has been declared to occur, namely, the gastric juice. Brugnatelli states 

 that fragments of rock-crystal and agate inclosed in tubes, and introduced into 

 the stomachs of hens and turkeys, were found in ten days to have lost 10 or 12 

 grains in weight. Trevieanus, also, is said to have found that chjnue from hens' 

 stomachs corroded porcelain capsules. These experiments are thought to prove 

 the presence of free hydrofluoric acid in the gastric juice. Tiedemann and 

 Gmelin placed the gastric juice of ducks in platina crucibles covered with plates 

 of glass, having lines traced on them through a coating of wax ; but found no 

 action on'the glass after 24 hours digestion with the aid of heat.* That hydro- 

 fluoric acid exists in the gastric juice of birds, in such quantity as to round off" 

 pebbles with the rapidity implied by Beugnatelli's observations, is not probable ; 

 but the force which is able to evolve hydrochloric acid at the stomach from the 

 chlorides which enter the system, is probably adequate, in similar circumstances, 

 to convert fluorides, along with the elements of water, into hydrofluoric acid. We 

 may now look for fluorine in all the animal fluids. 



7. Of the presence of Fluorine in Fossil Bones, and its relation to Animal Life. 



The facts detailed in the preceding sections remove much of the difficulty that 

 has attended previous speculations as to the source of the fluorine found in fossil 

 bones. It will now be conceded, that water must be constantly conveying that 

 element into the organs of animals, whilst other portions are also added in their 

 solid food. Whether this fluorine be supposed simply to travel through the 

 organism, dissolved in the circulating fluid as fluoride of calcium, or as some other 

 salt, and to quit the body as it entered it, without serving any purpose therein ; or 

 be imagined to fulfil some important end in relation to the functions of life, it 

 must be expected to shew itself as a very frequent, if not constant, ingredient in 

 the bones. We may quite safely infer that a portion, at least, of the fluorine 

 found in fossil osseous remains must have been present in them when they were 

 parts of a living structure ; and when we flnd only two per cent, of fluoride of 

 calcium in many ancient bones, while certain recent ones contain nine per cent., 

 it may well be doubted whether a trace of the salt has been added during fossili- 

 zation. Nay, it is a question I think worthy of discussion, whether there may not 



* These speculations will be found noticed in Berzeiius' Traite de Chimie, or in Simon's Animal 

 Chemistry, vol. ii., art. Gastric Juice. 



VOL. XVI., PART II. 2 S 



