114 Professor How on Natro-boro-calcite, &c., 
“hard plaster” (anhydrite) with the “‘ soft plaster” (gypsum). I 
detected it in the form of an opaque white substance without lustre, 
and, to the naked eye, devoid of crystalline structure, in cakes and 
somewhat rounded masses, varying in size from that of a small pea 
to that of a bean; these masses lay between gypsum and crystals of 
glauber-salt, taking shape from the crystals of the latter on the side 
next to them, and, when detached from them, leaving their faces, as 
it were etched, and sometimes the crystals were penetrated to a 
considerable depth by the imbedded borate. The mineral is very 
soft, H=1, but coherent, tasteless, slightly tough between the teeth, 
fuses readily before the blowpipe to a clear bead, insoluble in 
water, soluble in hydrochloric acid. As found, or very soon after 
being brought home, it lost by exposure to the air,— 
Water = 18°36 per cent., 
aud the air-dried substance gave the following results on analysis ; 
the water was determined by ignition; the lime, magnesia, and sul- 
phuric acid in one portion of the so dried residue, and the soda in 
another, after its treatment with fluor-spar and sulphuric acid for 
elimination of boracic acid, which was, of course, estimated by de- 
ficiency :-— 
Is II. 
Lime, ; is . : 14°21 
Soda, ; : : ‘ 7°25 
Sulphuric acid, . y : 3°98 
Magnesia, EK: 2 0°62 
Water, . n hs : 19°96 20°78 
Boracic acid, 3 E : 53°98 
100°0 
The quantity of mineral obtained did not permit me to make more 
than one analysis and retain a little as a specimen for identification ; 
but these results, as well as the characters already mentioned, and 
the crystalline structure to which I shall presently advert, are, I. 
think, sufficient to show that it is specifically distinct from Natro- — 
boro-calcite (see analyses, p. 429). On the assumption that the 
magnesia and sulphuric acid are accidental, and that the latter is 
combined with the former, and with a quantity of soda equivalent to 7 
that of the acid not required by the magnesia, I have calculated the 
preceding results (1.) after making these deductions, and at the same 
time taking away the amount of water necessary to render the 
MgO SO,=Mg0 SO, +7 aq. (the hydrated sulphate of soda would — 
