142 ESSAY VIII. 



foregoing experiment, again obtained alum. This laborious 

 experiment I repeated seven times, and always obtained 

 alum ; I now thought it reasonable to believe that Baume 

 was right. But, behold ! on examining the crucibles employed 

 for these repeated fusions, I found them everywhere uneven 

 in the inside, and full of little excavations, which they had 

 not before the experiment. This created a suspicion that 

 the alkali had perhaps dissolved part of the clay of these 

 crucibles, and thus, with the superfluous vitriolic acid, 

 produced alum ; I therefore now took an iron crucible, and 

 prepared the liquor silicum, which I treated in the same 

 manner as before, and obtained no alum. How easily may 

 one err in making experiments ! Thus all the alum I 

 obtained came from my crucibles, and I was in a fair way 

 to obtain conviction of a falsehood. Undoubtedly the same 

 thing led Mr. Baume into the mistake. I afterwards took 

 precipitated siliceous earth while it was moist, and digested 

 it for a fortnight with diluted vitriolic acid, in order to find 

 out whether, as Mr. Baume asserts, anything is dissolved, but 

 could find not the least mark of solution. 



The siliceous earth, therefore, still remains a peculiar 

 earth. Mr. Baume pretends that clay contains a little 

 vitriolic acid, and is on this account soluble in a large 

 quantity of boiling water. I likewise tried this experiment, 

 but found that, of several kinds of pure argillaceous earth, 

 not the smallest quantity was dissolved, which is easily 

 ascertained by means of alkali of tartar. I here likewise 

 made different experiments, in order to obtain vitriolic acid 

 from pure argilla, but without success. I could never obtain 

 any hepar by means of alkali of tartar, nor by means of 

 powder of charcoal ; neither have I obtained with clay a 

 vitriolic neutral salt from the residuum of the distillation of 

 muriatic and nitrous acid. 



