niently operated on at once. The reduction of the blood to ashes was a tedious and not very pleasant process, but with the help of a powerful furnace, and the active co-operation of my assistant, Mr Stevenson Macadam, who took great pains with the whole preliminary operations, I succeeded in the course of a month in reducing the whole quantity to wellburned ashes.

These ashes contained some unburned charcoal, but not in large quantity; in greater part they presented the appearance of two distinct substances; the one a dark-red solid, owing its colour to the presence of peroxide of iron, the other a white fused salt, having a strong, pure, saline taste, and consisting in greater part of chloride of sodium. The presence of this substance interfered with the detection of fluorine, by evolving a large volume of hydrochloric acid, when the ashes were treated with oil of vitriol, which carried away the hydrofluoric acid evolved simultaneously. It was necessary, accordingly, to remove the chloride of sodium before seeking for fluorine; and to avoid the risk of introducing the substance sought for, by the employment of reagents which might possibly contain it, I effected the removal of the salt by simply digesting the powdered ashes in a minimum of distilled water. This risked the removal of a little fluoride of calcium, or any other soluble fluoride which might be present, but precluded the possibility of any such compound being added to the ashes. After being washed accordingly, they were dried, and warmed with oil of vitriol in a lead basin, covered by a square of waxed glass, which had the words, Blood, 5th July 1850," traced upon it by a blunt style in the ordinary way. The whole of the ashes were employed with one piece of glass; but as the vessel could not contain the entire quantity in one charge, it was divided into two portions, the first of which remained for five days in the basin, and was then replaced by the other. The glass was thus exposed for ten days continuously to the vapour arising from the acidified ashes. They effervesced very slightly when treated with sulphuric acid, but evolved a sharp acid odour. The lead vessel was kept at a temperature of about 150° Fahrenheit during the day, and fresh quantities of oil of

66

vitriol were added at considerable intervals, and the contents of the basin occasionally stirred. The glass, which was cooled on the upper surface by the frequent renewal of a stratum of cold water, slowly became dim, and slightly opalescent where the letters were traced, in consequence, no doubt, of the separation of silica, for the letters appeared deeply etched when the wax was cleaned off. From the large scale on which the experiment was conducted, and the simplicity of the process followed, the evidence in favour of the presence of fluorine in the blood of the ox seems unexceptionable; and it cannot be doubted that the blood of other animals will be found to contain the same element. I have detected it in the blood of the horse. I presume it to be present in the state of fluoride of calcium, and that its amount is very small, but I have not attempted its quantitative determination.

Milk was examined in a similar way, but its reduction to ashes was much more easily effected than that of blood. I failed, however, to obtain other than the faintest indications of fluorine from the ashes of about 20 imperial pints of cows' milk. It was from a town dairy, and left a suspiciously small residue of solid matter. The main cause of the failure, however, I believe to have been the neglect to deprive the milk-ashes of the chlorides they contained. The experiment was repeated, with nine imperial pints of rich milk from a country farm, the ashes of which were washed with a minimum of water, dried and treated like those of blood. vapour which they evolved, etched glass distinctly. The ashes of 12 lbs. of new skim-milk cheese made this spring, treated in the same way, occasioned deep etching of glass. The ashes of four imperial pints of whey treated in the same way, have barely marked glass, so as to shew the faintest outlines when breathed upon. In all probability the fluoride of calcium is associated with the phosphate of lime present in milk, and when the latter is coagulated, separates along with the caseine.

The

I need not remind the Section that fluorine was long ago detected in another of the animal fluids, namely, urine, as well as in the skeletons, both external and internal, of, I may

say, all classes of animals. time, in accounting for the mal tissues and secretions. of calcium is soluble in water, and is present in many natural waters, and that it, or some other salt of fluorine, exists in the two great formative liquids of the animal organism, milk and blood, we shall cease to wonder at its presence in the animal solids and fluids, and begin to enquire what its functions may be.

Some difficulty was found at one presence of fluorine in the aniBut when we learn that fluoride

I would suggest, in conclusion, to those who may wish to repeat or extend this enquiry, that

1st. Substances to be tested for fluorine in the way described, should as much as possible be freed from the salts of volatile acids. Much washing, however, must be avoided, as it may occasion loss of fluorine; and if complicated processes are followed, care must be taken that the reagents made use of, are free from fluorine.*

2nd. Substances examined for fluorine, should generally be left for at least twenty-four hours in contact with sulphuric acid. If they contain, as they generally do, some compound of calcium, the pasty sulphate of lime produced, will obstinately retain the hydrofluoric acid, so that unless the mass is occasionally stirred, and the glass left for some period exposed to the vapour evolved, no etching may be obtained, although an appreciable quantity of fluorine is present.

Com

On the extent to which Fluoride of Calcium is soluble in water at 60° F. By GEORGE WILSON, M.D., F.R.S.E. municated by the Author.t

In 1846, I reported to the Chemical Section of the British. Association the result of an enquiry into the extent to which

* Chloride of sodium, and, therefore, hydrochloric acid, are liable to contain fluorine derived from sea water. Phosphorus, phosphoric acid, and phosphates are associated in nature with it; and so, though to a much smaller extent, are the insoluble salts of lead and the alkaline earths.

1850.

Read to the British Association, at its Meeting at Edinburgh, August 6th,

my re

fluor spar is soluble in water at 60° F. The result of searches at that period was, that 7000 grains of distilled water dissolve gr. 0.26 of the salt in question, at the temperature mentioned. Some objections were afterwards made by Mr Nisbet, to the method of investigation followed in some of my experiments, which seemed to imply that a doubt was entertained, whether the substance dissolved by water when it is digested on fluor spar, is fluoride of calcium, or the fluoride of silicon and calcium. I did not see the force of those objections, but I felt, nevertheless, that as all the solutions had been procured by boiling water on native fluor spar in glass vessels, which became slowly corroded if long exposed to the action of the solution, it was not impossible that silicon might have been present, in some of the solutions which were employed to determine the amount of solubility of the fluoride. I thought it well, accordingly, to repeat the results with solutions made in metallic vessels, and never allowed to come in contact with silica in any condition.

One set of trials was made last summer (1849) in the following way :-Well crystallised, transparent fluor spar, was boiled for some hours in a platinum basin, with fine hydrochloric acid, so as to secure the conversion of any silica possibly present, into fluo-silicic acid, and remove any metallic oxide, sulphate of lime, carbonate of lime, or other foreign matter present in the spar, and soluble in the acid. The purified fluor was then washed in the same vessel, by copious affusion with warm distilled water, and in this state employed for the preparation of the solutions to be evaporated. An aqueous solution was prepared by boiling distilled water on this purified salt contained in a platinum basin, and the liquid was then transferred to a pewter vessel, in which it was collected and left for some days at the temperature of 60°, that it might deposit the excess of fluor it had dissolved at 212°. The clear liquid was then filtered through a tin funnel, with the neck partially choked by zinc filings, and the filtrate was measured in a pewter vessel, which had been carefully graduated, so as to contain, when nearly full, 7000 grains of the solution at 60°. The liquid thus obtained and measured, and which had never come in

contact with silica, was then evaporated to dryness in a platinum capsule, and the amount of residue ascertained. Six careful trials were made, and gave as a mean, gr. 0.25166 as the amount of fluoride of calcium soluble in 7000 grains or 16 fluidounces, i. e., a pint (Old Apothecaries' Measure.)* This result approaches so closely to that previously obtained with glass vessels, that the number found must be considered as making a near approximation to the truth.

A similar series of observations was made this summer, but the fluor spar, which was of great apparent purity, as furnished to me through the kindness of Mr Tennant of London, was not subjected to any preliminary treatment with hydrochloric acid, but simply boiled with distilled water, and the solution collected and cooled as before, in a pewter vessel. The liquid was allowed thus much contact with silica that it was passed through a paper filter placed within a tin funnel. Few, however, I think, will suspect that it can have transferred to itself any silica from the saline constituents of the paper. Six trials were made in this way, the mean of which gave gr. 0-26 as the quantity of fluoride of calcium soluble in 16 ounces of water. The numbers, of which this is the mean, like those obtained in the previous determinations with metallic vessels, differ more from each other than the numbers did in the first series of experiments, where the solutions were made in glass flasks. This, however, was to be expected; for the liquid employed in the first series was prepared at once to the extent of many pints, and the uniform composition of the whole secured, before any the solution was evaporated. In the case of the metallic vessels, on the other hand, owing to their smallness, each pint had to be prepared separately, and its evaporation completed before another was procured. The numbers, therefore, could not but differ more in the second and third determinations than in the first. The highest number was 0:28, the lowest 0.24. We may therefore consider 0.26 as sufficiently nearly representing the true solubility of fluor spar,

of

In the report of the British Association for 1846 this amount of liquid was inadvertently called the imperial, instead of the (old) Apothecaries' pint.