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The aqueous solution of fluoride of ealcium was found:to give with 
salts of baryta a precipitate, which required a large addition of hydro- 
chloric and nitric acid to dissolve it. 
The author pointed out the difficulty which must in consequence occur 
in distinguishing between fluorides and sulphates, and suggested that 
fluorides may have been mistaken for sulphates in the analysis of min- 
eral waters. He referred also to the objection which must now tie 
against the present method of determining the quantity of fluorine pres- 
ent in bodies, consisting as it does in converting that element into fluo- 
ride of calcium, which, in the course of the necessary analytical opera- 
tions, is washed freely, and must be seriously diminished in quantity ; 
a fact which has of necessity been hitherto overlooked. 
Dr. Wilson stated, that he was not yet able to suggest an unexcep- 
tionable quantitative process; but that, at all events, the fluoride of ba- 
rium, being much less soluble than the fluoride of calcium, might in the 
meanwhile be substituted for it in the examination of fluoride. 
The author then proceeded to state, that, in consequence of the ob- 
servation he had made as to the solubility of fluoride of calcium in 
water, he had been led to look for that body in natural waters, and had 
found it in one of the wells of Edinburgh, viz. in that supplying the 
brewery of Mr. Campbell, in the Cowgate, behind Minto House. At 
the same time he stated, that preceding observers had already found it 
in other waters; He believed however, that he was the first to detect 
it in sea water, where, by using the bittern or mother-liquor of the salt- 
pans in which water from the Frith of Forth is evaporated, he had found 
it present in most notable quantity. The author referred to the presence 
of fluorine in sea water, as adding another link to the chain of observed 
analogy between that body and chlorine, iodine and bromine. 
_ Dr. Wilson further stated, that he had confirmed the observations of 
Will as to the presence of fluorine in plants: and Berzelius’s discovery, 
that fluorine exists in the secretion from the kidneys; and had, in addi- 
tion, detected fluorine in milk and blood, in neither of which has it hith- 
erto been suspected to occur. The paper concluded by some observa- 
tions on the presence of fluorine in fossils, and its relation to animal 
Ca 
15. Remarkable Discoveries in Iomorphism ; by M. Scuerrer, (ina 
letter to B. Silliman, Jr., from Berzelius, dated March 10, 1846.)— 
Mr. Scheerer has just found that in compounds containing magne- 
sia, protoxide of iron, oxide of nickel and other oxides isomorphous 
with magnesia, a part-of the base may be wanting without a change 
of crystalline form, provided that this part be replaced by a quan- 
tity of water which contains three times as much oxyaen as this part 
of the base. For seven the compounds Me°Si, Mg?Si+-33, and 
