COMPARISON OF DIFFEREXT KINDS OF Al.lJM. 279 



loto the limpid solution of each, when completely dis- 

 solved, they poored muriate of barnes to saturation, and 

 even adJed a very slight excess, that they might be certain 

 all the sulphnric nt'id was throwii down. Each of the solu- 

 tions required precisely the same quantity of muriate of 

 barytes. The precipitates were washed in 90 quarts of 

 water; and wlieu that of the last washing was rendered but 

 very slightly turbid by nitrate of silver, as the water vised 

 for the purpose itself was, they were collected with the 

 greatest care. 



After being dried, and calcined at a red heat for an hour, 

 the weight of the sulphate of barjtes produced was: 



No, grammes. 



1 , Roman alum 489-42 



2, Alum of Bouvicr 45)070 



3, ■ Liege 490*27 



4, Javelle 490*27 



5j -. Curaudau •••• 488*23 



Mean of the whole • • 489*63 



Messrs. Thcnanl and Roard adopted the proportion of 26 

 per cent of sulphuric acid in sulphate of barytes, because it 

 is the mean between the results of the anHi}'Sis of this sul- 

 phate obtained by one of them, and those found by Mr. 

 Berthollet after experiments made with the greatest care» 



The determination of the proportion of sulphuric acid ' 



being the most important experiment, they attempted it a 

 second time with as much precision as beiore, and found no 

 difference between the quantities of sulphate of barytes ob- 

 tained by the two analyses. 



Exp. 2. The equal quantities of sulphate of barytes ob- For the alu- 

 tained by Messrs. Thenard and Roard in the preceding tnals min^^* 

 leaving them no doubt with respect to th*^ projiortions of sul- 

 phuric acid in the alums they had examined, they did not 

 think it necessary to analyse any but those oi Rome, Bduvier, 

 and Liege, for the purpose of acertaining the proportions of 

 the other principles. These give us one artificial alum, and 

 two native alums, of which one is the most common, the 

 other the most esteemed. Of each of these 4S9 grammes v 



well 



