FLUORIDE OF CALCIUM IN WATER. 155 
rapidly corroded than those employed in the similar establishments in the Canon- 
gate. As the action of the water may be supposed to be the same at both places, 
and the attending circumstances similar, it must be some constituent of the Cow- 
gate wells that occasions the difference. It may be the fluoride of calcium.* 
To conclude this part of the subject, I may state that Dr Curistison informs 
me, that he has frequently had occasion to notice that considerable quantities of 
natural waters evaporated to dryness in glass basins, permanently destroyed the 
transparency of the latter. From all that has been mentioned, it will appear 
that fluorine is likely to prove a frequent, though not an abundant, constituent of 
ordinary water. If the proposal to construct the pipes of our water-works of 
glass be put into practice, we may have an opportunity, on the large scale, of 
testing the truth of this idea. 
It follows as a corollary, from the truths already detailed, that fluorine must 
be present in sea-water. ‘The inference that it must be there, had been drawn 
by Mr Mippteton from the fact, that fluoride of calcium occurs in the shells of 
marine mollusca.+ SILLIMAN junior has come to the same conclusion, apparently 
without a knowledge of MipDLETON’s views, in consequence of invariably finding 
the same fluoride in calcareous corals.t In the teeth of the walrus and of the 
shark, the only marine animals I have examined, I found fluorine very distinctly, 
especially in the latter. 
I attacked the problem, however, directly, by examining the water of the 
Frith of Forth. <A portion of the mother-liquor or dittern, from the pans at 
Joppa, near Portobello (three miles from Edinburgh), in which sea-water is con- 
centrated so as to yield culinary salt, was precipitated by nitrate of baryta. The 
precipitate, after being washed and dried, was warmed with oil of vitrol in a lead 
basin, covered by waxed glass, with designs on it. The latter were etched in two 
hours, as deeply as they could have been by fluor-spar treated in the same way, 
the lines being filled up with the white silica, separated from the glass. To the 
acknowledged constituents of sea-water, fluorine, then, must now be added. 
* As the fact of the frequent presence of fluorine in water must hereafter enter as an important 
element into all speculations as to the cause of the corroding action of water on glass, I place here on 
record the result of an accurate quantitative trial on the latter subject. 
I am indebted to Mr Joun Aniz for the particulars of the following experiment, which was made 
with a view to discover what peculiarity in the structure of glass unfits much of it for optical purposes. A 
cube of glass, two and a half inches square, was inclosed in a fir box, and fixed immovably in it by pieces 
of wood. Holes were pierced in the sides of the wooden case, so as to permit the free passage of the 
water, and the whole was placed in an engine-boiler, supplied with the Edinburgh pipe-water, and left 
there for six months. During that period the boiler was in action twelve hours each day ; the water 
being under a pressure of 35 pounds on the square inch, and at a temperature of about 260° Fahr. The 
cube weighed, when first immersed, 9157 grains, and, when taken out, had lost 457 grs., or about 34th 
part of its weight. It is right to mention, that the condensed steam was returned to the boiler, so that 
fresh saline matter was only furnished in the water added, from time to time, to supply the waste. 
+ London Phil. Mag., No. 144, p. 14. 
{ On the Chemical Composition of Calcareous Corals, by B. Sizniman junior.—American Journal 
of Science, vol. i. Second Series. 
