COMPAUISON OF DIFFEllENT KIIJDS Of ALUM. SSV 



The weights of the sulphate of potash thus obtained 

 were : 



- No. 7 gtammes. 



1, Roman alum 77*05 



2, Alum of Bouvier 76*80 



3, Liege • 77*33 



These sulphates no longer gave any sensible precipitate 

 with oxalate of ammonia, and rendered nitrate of silver but 

 very slightly turbid. They contained a little excess of alkali, 

 but in so small a quantity, that a few grains of sulphuric 

 acid were sufficient to saturate it. 



Messrs. Thenard and Roard preferred treating the sulphates 

 with lime to employing calcination, for they had satisfied 

 themselves that by calcination acidulous sulphate of potash 

 can only be obtained, part of the alkali always flying off. 



The analysis of the sulphate of potash, repeated several Constituent 



times following, constantly afforded them the same results, P'^^"^^^^^^ of 



r 1 • 1 ■ r sulphate o^ 



and showed, that a hundred parts of this salt consist of potash. 



Sulphuric acid 36*4 



Potash 63'6 



100 ' 



Exp. 4. Desirous of knowing whether the alums they had Analysed foi- 

 analysed contained ammonia, they treated them with caustic ^"^"^o"^^* 

 potash, and with lime; and as they obtained none by this but none 

 method, they heated jhem strongly in a retort with an equal ^o^nd. 

 weight of powdered quicklime; but they could not thus 

 discover the slightest trace of it. In fact, say the}-, we 

 should have been surprised, if we had found any, for we 

 knew to a certainty, that it could not be one of the consti- 

 tuent parts of the artificial alums we examined; and as to 

 the native alums of Liege an<i Rome, as no urine is added in 

 their preparation, the ammonia mnst have existed in the ore, 

 and from this it must have been expelled by the roasting. 



We m>ust not however conceal, that it is possible to find Mayexi^tin 

 alums with an aniinoniacal base, though they must be very *^"''^ ^^""^* 

 rare, for the practice of saturating the excess of acid in the 

 aluminous lixivia by means of urine has been very confined, 



as 



