34 ttcfearchcy- on Alumine, 



There is another earth of the fame kind, but much freer from 

 foreign principles. It is denoted in mo(t authors under the 

 name Or the pure argil of Hales (re'ine thonefde de Wertitr)* 

 the place where it was found., in the garden of the college of 

 Hales, and in the neighbourhood of an apothecary's fliop ; 

 its exterior form, its {'mall quantity, and its purity, have made 

 fome authors fuppofe that it was a production of art. Thig 

 may he, but it merits no lefs the attention of naturalills, fince 

 it has characters whieh alumine prepared artificially has not. 

 M. Lenz fays, the pure argil is found in other places than at 

 the college of IJalcs ; but lie does not fay whether it be cry- 

 ftallized like that whieh is here alluded to. 



M. Schreber, who analyied this fubttance, confiders it as 

 a combination of alumine with carbonic acid, water, and a 

 little lime, filex, iron, inflammable matter, and, fometimes, 

 gypfum. I have not been able to procure the details of the 

 labour of this naturalift on this earth, but the fmall quantity 

 (about live grammes or 77 grains) which I had at my dif- 

 pofal was fufficicnt to perfuade me that it contained no car- 

 bonic acid. I ihall here defcribe the principal external cha- 

 racters of it, according to thefpecimens from which I obtained 

 my refults. It is as white as fnow; its external form is kidney 

 or muili room ; it has a fine earthy frafture, is tender and al- 

 moin friable; adheres little to the tongue, is fomewhat trans- 

 lucid at the edges, and feems fine to the touch, but not fat*. 



* Pure fpongy or gelatinous alumine is not Fat or un£tuous, or at leaft 

 if is nor more fo than anv Other earth reduced to the farce flate of divifion ; 

 loes not even become fo by being mixed with water after it has been 

 dried at the temperature of the atmofphci e. Under thefe circumftances 

 it cannot refoive itfelf with that liquid into a connected pafle, more or lefs 

 vifcous, like the greater part of the native clays : alumine is indebted for 

 it; un£h)bflty, which is improperly confidered as one of its effential cha- 

 racters, only to its mixture with other fubftances. 



The cafe is the fame with the earthy odour, which is confidered as effen- 

 tial to moiftcned alumine, and which, in my opinion, does not belong to 

 this earth, when difengaged from every combination. It is found that 

 this odour decreafes in argil in proportion as it is deprived of the oxide of 

 iron. M'»litened alumine, obtained from common alum, affects the organs 

 of fmell in u rtianher fcarcely fenfible ; but the earthy odour no longer 

 .; in ;ii limine pmified by potafh, when it has been again moiftened. 

 after bein^ dried in the common temperature of the atmofphcre. If a de- 

 licate fmell can diftinguifli it at the moment of its precipitation, it is be- 

 caufe the alumine, aftef hiving been diffolved once in potafh, retains a 

 Imall quantity of the oxide of iron ; toe alumine, purified in one operation 

 by rhis laft procefs, can furnith by alkaline pruifiates, a quantity of pruiliate 

 ; -on very fuperior to that which, always exifts in the pureft alkaline 

 nrulliates. By moan-, or trituration with oxide of iron, i communicated to 

 inodorous alumine an aluminous or earthy odour. It is poifible that this 

 fubftance may commumcitc the fame odour to other earths, for Vauquelin 

 found that fome chalcedonies exhaled an aluminous odour when triturated, 

 'hough they contained no alumine. 



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