FLUORIDE OF CALCIUM IN WATER. 1538 
Moravia.* MippLEeTon has found it in the London pipe-water, and in three 
other waters, the localities of which he does not mention; but as the experiments 
were made in London, they were probably English. Traces of it have been found 
in other waters also. 
I was induced to search for it in the water used in certain of the breweries 
in Edinburgh, in consequence of learning that these rapidly corrode the ther- 
mometers employed to regulate the temperature of the boilers and vats. The 
fact was first mentioned to me by a gentleman, who, before I made any trials on 
the subject, inferred that the corrosion of the glass must be owing to the pre- 
sence of a fluoride in the water. I discredited the statement when I first heard 
it, supposing that an incrustation or deposition of sulphate and carbonate of lime 
had been mistaken for a true corrosion. I thought it impossible, moreover, that 
fluoride of calcium, even if it were present, could act upon glass. But in the 
course of the experiments already detailed, I had once occasion to notice that a 
new Berlin porcelain basin, in which a considerable quantity of the aqueous 
solution of fluoride of calcium was boiled down, had its glaze completely re- 
moved. On observing this fact, I applied to our intelligent instrument-maker, Mr 
Stevenson, through whose hands the greater number of the thermometers used 
by the Edinburgh brewers pass, in the course of receiving necessary repairs. He 
informed me that he was quite familiar with the rapid dimming of the thermome- 
ters, and that it was a true corrosion; in proof of which he gave me two pieces of 
broken thermometers, which I shew the Society. They are certainly abraded, 
and present a surface like that of ground glass. The roughening which is so 
manifest was not the result of friction against the sides of the brewing vessel, or 
any other kind of mechanical action; for the corroded part of the thermometer- 
stem was enclosed in a brass-tube, and completely protected from external 
violence. It is proper to mention that the workmen in some of our breweries are 
in the practice of scraping the stems of their thermometers, to remove the de- 
posit of lime-salts which rapidly gathers on them, and are ready to affirm that 
the apparent corrosion is an abrasion occasioned by their own knives. To guard 
against the possibility of any deception having occurred in this way, I visited the 
brewery of Mr CampseELt, situated in the Cowgate, behind Minto House, and was 
shewn by his manager a thermometer which had never been scraped with any 
instrument, and had been in use only a few weeks, but was nevertheless so 
dimmed, that it required to be dipped into water in order to confer upon it a 
temporary transparency, before the included mercury could be distinctly seen. 
Mr Stevenson informs me that he finds the protected parts of the thermometer- 
stems, which are enclosed in brass-tubes, as much corroded as those which are 
exposed. 
* Bulletin des Sciences Medicales, vol. xvii. p. 425. From Zeitschrift fiir Physik und Mathematik. 
VOL. XVI. PART II. 2 Q 
