1^4 "Refearcbcs on Alumine, 



when the alumine is in the fpongyftate: it is liable to an 

 error of fifteen hundredths when it is in a gelatinous ftate; 

 and in that cafe, nothing ean be done but to dry it at a tem- 

 perature between the 65th and 90th degree of Reaumur, and 

 to diminim its weight in the iatio of 58 pereent.; or, what 

 is Itill better, to ctVe6t its folution, and precipitate it in the 

 fpongv (late. If this earth, then, dried at the temperature of 

 the atmol'phere, does not lofe at a red heat about 58 hun- 

 dredths of its weight, it may be prefumed that it is pure. 



Considerations on the Application of gelatinous Alumine to 

 Pyrometry, 



Gelatinous alumine experiences, at a heat fuccemVely aug- 

 mented, loiTes of weight which, at equal intervals of heat, foU 

 low a decreafing progrefTion ; to know the law of which would 

 be very important, becaufe they might ferve for eftimating, in 

 a preeife manner, the different degrees of heat. I afcertained, 

 by repeated experiments, made with care, that the quantity 

 of water it lofes is invariable; that is to fay, that when the 

 earth has attained its maximum in regard to lofs of weight at 

 a certain degree of heat, the continuance of the heat at that 

 degree has no influence in producing any further deficcation. 

 Though the experiments I made in other refpecls, to obtain 

 foine information on the poffibility of applying gelatinous 

 alumine * to pyrometry, were far from affording me fatisfac T 

 tion, I mall defcribc them with all their imperfections. They 

 will be of l'ome ufe to thofe who may have perfeverance 

 enough to purine thefe refcarches. — A hundred parts of gela- 

 tinous alumine in powder, and dried at the temperature of from 

 65 to 88 degrees of Fahrenheit, lofe at the temperature of 



Thefe 



* As fpongy alumine abandons all the water it contains at a flight in- 

 eandcicence, it can be employed only for lower degrees. 



f The (hrinking of pyiometiic cylinders, and, in general, of argils, by 

 heat, is afcribed to the expulfipn of water. T^s opinion is true beyond 



v a doubt; 



