158 COMPOSITION OF SULPHATES, 



whence I conclude, that in 100 parts of potash purified by 

 Proportions of a i co hol there are 27*5 of water; and, setting out with this 

 kU V * " datum, that the potash in 100 parts of sulphate of potash is 

 57*7 1, instead of 52 as assigned by Bergman. 



I cannot omit remarking however, that the analysis of 

 alums by Mr. Vanquelin* demonstrates the presence of sul- 

 phate of potash in them nearly in the same proportion, as 

 appears from synthesis : a result showing the confidence to 

 be placed in the analyses of that learned chemist, and leaving 

 us to regret, that he relied on Beryman for the proportions 

 of acid and base in the sulphate of potash. 

 Experiment to Exp. 4. Desirous of knowing the proportions of acid and 

 ■fin the F°- ] )ase \ n n itrate of potash, I dissolved by the assistance of heat 



portions of acid . 



and base in ni- 100 gr of very dry nitrate of potash in 800 of a solution of 

 (rate of pot- su iphate of alumine at 34 [sp. gr. 1-307.] After the liquor 

 was cold, I obtained 376 gr. of alum. The mother water was 

 set to evaporate again, but as it crystallized confusedly I 

 added 10 gr. of sulphuric acid at 66° [sp. gr. 1*848], because 

 experience had taught me, that whenever such a solution 

 contained an acid foreign to the alum, an excess of sulphuric 

 acid was necessary to promote the crystallization of the alum. 

 In fact, as soon as this mixture was made, a considerable pre- 

 cipitate took place, which, after being drained and dried, 

 weighed 84 gr.. Lastly to satisfy myself whether the mother 

 water still contained alum, I added anew 100 gr. of the so- 

 lution of sulphate of alumine. This addition, increasing the 

 density of the liquid, favoured the precipitation of the small 

 quantity of alum, which it still held in solution. When this 

 last product was drained and dried, it amounted to 2 gr. ; 

 which, with what was obtained before, made 462 gr. of alum. 

 As it had crystallized however in a liquid containing princi- 

 ples foreign to its composition, it became necessary to purify 

 it. With this view I dissolved it, and crystallized afresh. 

 From this process, I obtained only 452 gr. of alum, but cer- 

 tainly very pure. 

 40-76 potash, This experiment, which T have repeated several times, 

 trie acid. " ar, d with different quantities, always gave me results con- 

 firming the former: whence I conclude, that if 100 gr. 

 of nitrate of potash produce 452 gr. of alum, 49.76 of 



• Sec Journal, 4to serks, rol, i, p 318. 



potash 





