66s PHILOSOPHICAL TRANSACTIONS. [aNNO 1790. 



small in quantity for any particular examination ; but which, from its aspect, from 

 the manner in which it was obtained, and from the taste of the lixivium before 

 the addition of the alkali, was judged to be the aluminous earth. The marine 

 acid, during digestion, seemed to have as little action as the other 2 ; but on 

 pouring in some water, with a view only to dilute and wash out the remaining 

 part of the acid, a remarkable difference presented itself; the liquor became 

 instantly white as milk, with a fine white curdly substance intermixed ; the 

 strong acid having extracted something which the simple dilution with water 

 precipitated. 



The white matter being washed off, more spirit of salt was added to the re- 

 mainder, and the digestion repeated, with a long tube inserted into the mouth of 

 the glass, so as nearly to prevent evaporation. The acid, when cold and settled 

 fine, was poured off clear ; and on diluting it with water, the same milky ap- 

 pearance was produced as at first. The digestion was repeated several times suc- 

 cessively, with fresh quantities of the acid, till no milkiness appeared on dilution. 

 The quantity of mineral employed was 24 grs. ; and the residuum, after the 

 operations, washed and dried, weighed somewhat more than 19 grains ; so that 

 about 4- of it had been dissolved. In some parcels of the mineral, taken up pro- 

 miscuously, the proportion of soluble matter was much less, and in none greater. 

 It is only the white part, and only a portion of this, that the acid appears to act 

 on : the white sand, much of the white soft earth, and all the black particles, re- 

 main unaltered. 



To try whether this tedious process of solution could be expedited by trituration 

 or calcination, some of the mineral was rubbed in a mortar ; and in doing this, 

 it appeared pretty remarkable, that though the black part bore but an incon- 

 siderable proportion tojthe rest, yet the whiteness of the other was soon covered 

 and suppressed by it, the whole becoming a uniformly black, shining, soft, 

 unctuous mass, like black-lead rubbed in the same manner ; with a few gritty 

 particles perceptible on pressing hard with the pestle. A penny-weight of this 

 mixture, spread thin on the bottom of a porcelain vessel, was calcined about an 

 hour, with a fire between 30 and 40 degrees ;* it became of a uniform, dull, 

 white, or grey colour, excepting a very few, and very small, sparkling, black 

 particles, suspected to be those which had eluded the action of the pestle ; it lost 

 in weight 6 grs. or a 4th part. The mineral, thus ground and calcined, was found 

 to be just as difficult of solution as in its crude state; with this additional dis- 

 advantage, that the undissolved fine particles are indisposed to settle from the 

 liquor. , 



• By degrees of fire, or of heat above ignition, I mean those of my thermometer ; and some idea 

 may be formed of their value, by recollecting, that they commence at visible redness ; and that the 

 extreme heat of a good air-furnace, of the common construction, is l60°, or a little more.— Orig. 



