0^30 COMPAEISON OF DIFFERENT KINDS OF ALUM. 



well powdered were dissolved- by heat in 16' quarts of water, 

 and decomposed by equal quantities of ammonia, which was 

 added in very great excess. The alumine precipitated was 

 washed with b'O quarts of water ; and whea that of the last 

 washing ceased to precipitate muriate of barytes, it was col- 

 lected, and dried in a large silver basin. After being dried, 

 and kept at a red heat for an hour, it weighed: 



No. gtammes. 



1^ Roman alum .... 60*92 



2, Alumofljouvier • 61*82 



3, Liege 6l-02 



Thus Messrs. Thenard and Roard found in these alums 

 exactly the same quantity of alumine ; for the Jrifiing differ- 

 ences observed between them do not amount to a gramme 

 [15 ~ grains], and are such as could not be avoided in such a 

 long series of operations. 



The authors took so -much care in washing the alumine, 

 and not pouring off the water till the sediment was com- 

 pletily formed, and liad left it perfectly clear, that they can- 

 not fear having assigned the quantity too small. Neither can 

 it be too great, i»iuce, when it was dissolved in nitric acid, the 

 solution did not render muriate of barytes turbid: it was 

 completely freed from any sulphate therefore, that might have 

 increased its weight. 



For the potash ^^P ^' '^^^ ^^ quarts of lixivium produced by washing 

 each of these alums were evaporated to dryness in a silver 

 bowl, and the products obtained were boiled several hours 

 with an equal weight of quicklime. The residuum was 

 treated four times successively with boiling water, to take up 

 completely every thing soluble; and these waters were'^va- 

 porated to dryness, the residuum dissolved in a very small 

 quantity of distilled water, and this repeated alternately se- 

 veral times, in order to separate completely the last portions 

 of sulphate of lirae. The solution of each of the sulphates 

 of potash was evaporated for the third time, and at length 

 heated red hot in ^ platina capsule. 



The. 



