210 
PROFESSOR FORCHHAMMER ON THE COMPOSITION 
observed under the microscope, and showed very few half-dissolved prisms of gypsum, 
but numerous very small octohedrons, which had been hidden by the gypsum. Besides 
these octohedrons, some hemiprismatic crystals were found, precisely similar to those 
which I formerly had obtained when forming a borate of magnesia. The powder con- 
tained, further, some prisms which were striated parallel to the axis, and had a face per- 
pendicular to this axis ; they resembled precisely the crystals which I several years ago 
described as artificial apatite, and which were obtained by fusing calcined bones with 
chloride of sodium ; and they were in fact apatite, formed of the phosphoric acid, 
fluorine, chlorine, and lime of the sea-water. Of the powder in question, which essen- 
tially consisted of octohedrons, I dissolved 7T84 grains in nitric acid, which left 0T60 
grain of a reddish powder consisting mostly of oxide of iron, but showing also under 
the microscope hemiprismatic crystals like the borate of magnesia. The nitric solution 
gave with ammonia a precipitate which weighed 0*633, and contained phosphoric acid. 
At last the remaining solution gave with phosphate of soda and an excess of ammonia 
16’667 ignited phosphate of magnesia=6‘074 pure magnesia. The sum of all these 
substances thus determined was 6‘867, so that only a quantity amounting to 0‘317 grain 
which was wanting could be boracic acid. 
It was thus clear that the octohedrons analyzed could not be boracite, and there could 
hardly be any doubt but that the substance was essentially pure magnesia, mixed with 
small quantities of oxide of iron, phosphate of lime, and other substances which were still 
to be determined. Pure magnesia occurs among the Vesuvian minerals crystallized in 
regular octohedrons, and has obtained the name of Periclase. In this case the periclase 
was formed by the decomposition of the hydrate of chloride of magnesium contained in 
the salt of sea-water, and decomposed in the melting heat. As a further proof of its 
nature as pure magnesia, it may be mentioned that, when boiled with a solution of sal- 
ammoniac, it was dissolved with a strong smell of ammonia. The solution contained 
magnesia, and nothing else besides salts of ammonia could be discovered. 
When the octohedral crystals were removed by boiling with a solution of sal-ammo- 
niac, the remaining powder contained only hemiprismatic prisms of the supposed borate 
of magnesia, crystals of apatite, and very acute six-sided pyramids, which in their form 
had some similarity to crystals of sapphire, and a considerable quantity of amorphous 
red oxide of iron, probably mixed with silica. A portion of this powder was moistened 
with sulphuric acid, and during twenty-four hours left to spontaneous evaporation. I 
could now observe crystals of sulphate of magnesia and needles of sulphate of lime. 
The substance, nearly dry, was mixed with diluted alcohol, which, when inflamed, showed 
the green margin of the flame characteristic of boracic acid, and gave a brown colour to 
curcuma paper, although the solution was acid. It is thus proved that this salt con- 
tained boracic acid, which in this case could only be derived from sea-water. When 
this powder was boiled with muriatic acid, apatite, borate of magnesia, and silicate of 
peroxide of iron were dissolved, and a very small quantity of the six-sided pyramids 
remained, which resisted the action of acids, but were made soluble by fusing with 
