144 ESSAY VIII. 



might see whether the gypsum would separate from the 

 water and precipitate with the solution of alum ; but this 

 did not happen, (e) I further wished to know how lime- 

 water would act upon the earth of alum. I found that it 

 very soon lost its caustic taste, and that the clear earth 

 of alum grew opaque. I strained part of this water, and 

 dropped some lixivium tartari into it, but it remained clear ; 

 neither was there any precipitate formed by corrosive 

 sublimate. I afterwards added muriatic acid to the last- 

 mentioned precipitate, when it dissolved entirely without 

 leaving any gypsum behind. Thus the earth of alum had 

 united itself with lime, and formed a peculiar compound. 



I now thought that this compound of the earth of alum 

 and lime might separate gypsum from water ; (/) I therefore 

 prepared a large quantity of this compound earth, mixed it 

 with a solution of gypsum, and set it to rest for a quarter of 

 an hour, when I saw, to my surprise, that the gypsum 

 remained suspended in the water, and that the precipitate 

 was still soluble in muriatic acid, without leaving any gypsum 

 behind, (g) I now mixed a solution of gypsum with lime- 

 water, adding also pure earth of alum. This mixture 

 perfectly agreed with that mentioned at (&). The precipitate 

 was white, and contained gypsum as well as lime. From 

 these experiments I conclude (1) That the vitriolic acid in 

 gypsum is able to combine with more lime than is requisite 

 for its perfect saturation. (2) That calcareous earth is 

 capable of uniting with the earth of alum. (3) That gypsum 

 cannot combine with the earth of alum ; but if a superfluous 

 quantity of lime be united with vitriolic acid, it then will 

 serve as a means of union to combine gypsum with the 

 earth of alum, and thus form a combination consisting of 

 three earths. Pure clay has no effect upon lime-water. 



