dfe On the difftrtnl EffeBs of the Jlkalis 



the native alum from M'tfeno, Only one part of its aqueous folution would cryftalllze Into 

 genuine alum, in which aifo he traced out the alkali ; the remaining portion of the lye 

 yielded np alum fpontaneoufly, but only when a little pot-adi had been fuperadded. 

 Bergman * likewlfe, found that alkali in the artificial alum, even In the Roman } and Prof. 

 Lampadiui'\ himfelf conGders It at prefent as an eflentlal-principler of alum. In confequence 

 of having found it in four different fpccles of fadlltlous alum : namely, thofe from Com- 

 mot'm and Weifsgrun In Bohemia, and thofe from Reichenhach, and from the Schwemfal In 

 Saxony. 



On confiderlng the fhare, which the vegetable alkali has In the produftion of alum, the 

 quellion naturally arlfes : whether ^sZ-zj/J alone, ox foda llkewife, as well z.% ammoniac.) are 

 capable of combining with fulphurlc acid and argillaceous earth Into alum % ? 



The aptitude of volatile alkali to enter Into fuch union, feems to be deduclble from the 

 circumftance, that, In fome alum-works, urine only and no pot-afli is employed. How- 

 ever, as I have already obferved In another refpeft, It Is not ImpolRble but that a quantity 

 of vegetable alkali may be afforded by aflies formed in the roafting of the alum-ore, fuffi- 

 clent to complete the alum. 



The alkaline portion of the alum may be afcertalned In three different ways by analyfis. 



1. Let the argil be thrown down from a watery folution of alum by means of ammoniac ; 

 caufe then the fait contained in the clear decanted lixivium to cryftallize, and fubfequent 

 to this expofe it to a fubliming heat. In this procefs, the fiilphate of ammoniac fubllmes, 

 but ihtfxedfulphate ofpot-a/Ij, if any has been In the alum, remains behind It In a compa6t 

 form. This method difcovers the prefence of fixed alkali only. 



2. To a boiling hot aqueous folution of alum, add carbonate of lime. ' By this manage- 

 ment the fulphate of argil is decompofed, and the lime Is converted Into gypfum •, at the 

 fame time that the fulphate of pot-afli, if any was prefent, remains unaltered. This lafl 

 would likewlfe be decompofed by cauflic or pure lime ; but it Is well known that the crude 

 calcareous earth, on account of its flrong attradtlon for carbonic acid, has no fuch power 

 on fulphate of pot-afh. What quantity of crude lime may be necefTary to accomplifh that 

 decompofitlon, may in fome manner be determined, by the known proportions of argil to 

 fulphurlc acid In alum, as well as by the proportion of calcareous earth to the fame acid in 

 gypfum, and laftly that of crude lime to carbonic acid Iir carbonate of lime. However, as 

 this determination is fubjccl to fome difficulties. It will be fufficient to be attentive to the 

 cfFervefcence of the lime, and according to this effect, to add rather too much than too 

 little, becaufe the redundant calcareous earth falls down, unchanged, together with the 



* Bergman, cit. § 77, page 307. Yet he fays : handraro^ 



•f- Lampadius, Praft. Chim. Abhandlungenll. 1797. S. 228. 



X Marggraf (cit. loc. page 1 96) fays only, that the addition of fixed alkali is necctZiry,— Lampadius 

 (cit. p. 230) has not yet given any refults of his experiments, made with the mineral and volatile alkali.— - 

 Bergman (cit. 307.) fays : crjjfallizationis obflaculum alcali volatili aque tollitur, non vero alcali minerali 

 et cake ; yet vifithout relating any experiment. 



precipitated, 



