the Laws of Affinity . 203 



lions oppofite to thofe which afforded fuch a change, would 

 not be at all affected by their mixture. 



8. I have examined what change might be produced in 

 the refults by a fubflance which has the property of forming 

 triple falts, fuch as magnefia. 



JVJ. Equal parts of fulphateof potafli and muriate of magnefia 

 afforded, 1. Sulphate of potafh ; 2. Sulphate of potafli, a little 

 muriate of potafli, and a triple fait, compofed of fulphuric acid, 

 potafh, and magnefia : this fait forms fine rhomboids, which, 

 by expofure to the air, do not lofe their tranfparency: its fa- 

 llibility is nearly the fame as that of the fulphate of potafli : 

 3. Muriate of potafli and fulphate of magnefia. The refiduum 

 contained fulphuric acid, muriatic acid, potafh, and magnefia. 

 N. Two parts of muriate of magnefia, and one of fulphate 

 of potafli, afforded, 1. Sulphate of potafli; 2. Muriate of 

 potafli, and the triple fait of the preceding experiment; 

 3. Muriate of potafli, and fulphate of magnefia: the refi- 

 duum was analogous to that of the preceding experiment. 



In experiment M, fulphate of potafli was obtained by two 

 cryftallizations ; but in experiment N, where the muriatic 

 ncid was in a greater proportion, it was obtained on the firft 

 cryflallization ; the triple fait, which in folubility nearly ap- 

 proaches the fulphate of potafli, cryftallized after the feeond 

 evaporation. When the proportion of fulphuric acid was 

 fufricientlv diminiflied by thefe cryftallizations, then the 

 muriate of potafli was feparated nearly according to the order 

 of folubility ; and laftly the magnefia, which being flill abun- 

 dant, cryitallized with part of the fulphuric acid. We fee 

 that, a different opinion might have been formed in thefe two 

 experiments, according to the period of the cryflallization at 

 which it might have been obferved; and how erroneous the 

 eftablifhed opinion is, that a complete change of bafes takes 

 place on the mixture of muriate of magnefia and fulphate of 

 potafli. 



In experiment M, where the fulphuric acid was prefent 

 in greater proportion, fulphate of potafh was obtained in both 

 the firft cryftallizations ; but in experiment N, where the 

 muriatic acid had more influence by its relative quantity, 

 fulphate of potaih only was obtained in the firft cryflalliza- 

 tion; the magnefia, for the moft part, remained in the un- 

 cryftallizable refidue, becaufe it has no force of cryflalliza- 

 tion with the muriatic acid, and only a weak power with 

 the fulphuric ; other falts which would cryftallize in other 

 circum (lance's, are retained in the refidue which oppofes their 

 cryflallization. The difference obferved between the refults 

 of ilfefe two experiments, and thofe of the experiments A,B, 



and 



