SUL

SUL ( S87 )

afferts that the artificial fulphat contains 2 percent, more acid than the natural.

Sulphat of Magnesia. Epfom Salt. BitterPurging Salt.

This ui'eful fait is occafionally found native,but by far the greater part is artificially pre-pared.

The native fait when folid is met with al-moft invariably in the form of fine capillarycryftals, on the furface of decompofing fchiltus,often in coal-pits, and not unfrequently effio-refcing on the furface of the foil. A very purefulphat of this kind is defcribed under the arti-cle Bitter Salt (which fee) and was foundin the mercury mines of Idria where it isknown under the name of Haarfilz, and wasmiltaken for plumofe alum till Klaproth de-tected its real .nature.

Fontana mentions 1 a large quantity of thisfait found in the quarries of gypfum in Pied-mont efflorefcing on the furface of the gypfum(particularly in thofe that are the molt expoied toth? fun,) which is brulhed off from time totime, and when diffolved in water and cryftal-lized is fold by the peafants.

Prouft u alfo relates that this fait abounds fomuch in many parts of Spain , that in Andalufialarge trails are covered with an efllorefcence ofit after floods; and in moll of the houfes ofMadrid , the foundation and krwer walls arecovered with this fait, which arifes from the de-compofition of the mortar, to the great detri-m ent of the buildings.

It^ is not unfrequent to meet with the famelalt m this country, forming a fine hair-likeialine covering to the walls of damp cellars,or new buildings. An efflorefcence of thiskind is noticed by Dr. Boftock v on the wallsof a new houfe near Liverpool, which wasvery pure fulphat of magnefia; and a fimilarproduction of this fait is mentioned by it Jr.Gregor, w on the furface of a wooden frameufed to fift coal-afhes, which latter on anaiyfiswere found to contain gypfum along with iul-phat of magnefia. In many of thefe infiancesthe lulphat of magnefia appears to arife froma decornpofiiion of fulphat of lime by magnefia,bar the precife mode in which this apparentcontradiction to the known order of airinitiesis brought about, is not very apparent. Inoarer cafes the pyrites commonly containedin coal appears a principal agent ir\ the pro-duction ot this ialt, for Mr. Gregor obtainedit in abundance by calcining for an hour a* Journ. de rhyf. torn. 33, p. 3 i a . . i !nd , tonl

mixture of about two parts of pyrites withone of lieatite, and after long expoiure to air,lixiviating the calcined mai's.

It is probable that many of the natural falineefflorefcences which have been fuppofed to benative faltpetre, may contain fulphat of mag-nefia.

Another fource of this fait is in certain falinefprings, and it is from thefe that our firltknowledge of .it originated.

It was firlt difeovered at Epfom in Surrey,by Dr. Grew, in the year 1675, in a mineralwater, to which it gave confiderable celebrity,and the fait iifeif was extracted by boiling, andwas fold at a high price as Epfom fait. 1 hefame fait was fometime afterwards fouild in awell at Shooter’s Hill in Kent, in the year 1700,which was alfo extracted by boiling down, andwas fold as Epfom Salt.

A few years afterwards it was found by forcechemifts that the fame fait could be preparedfrom the bittern or mother water of fea-water,after all the muriat of fodahad been extracted fitthe ufual method, and which ufed to be thrownaway. 'I bis procefs was long kept as a lucra-tive fecret in the hands of a few Lalt-makers,and the fulphat of magnefia made at the brineworks at Portfmouth and Lymington beingafforded much cheaper than could be done bythe evaporation of the mineral waters of Epfomor Shooter’s Hill, the latter gradually fell intodilufe, and for many years almoft all the vitriol-ated magnefia ufed in this country has beenprepared at the fait works at Lymington .

This fait was long confidered as peculiar tothis country,* and large quantities were ex-ported into other parts of Europe , and foldunder the name of Englif.i or Epfom Salt. Itwas afterwards difeovered in the mineral waterof Seydfchutz or Sedlitz in Bohemia , whence italfo obtained the name of this water, the cele-brated Hoffman having fbewn its identity withthe true Epfom fait. Sulphat of magnefia waslong confounded with fulphat of foda,, andthough fuflicient marks of diftinftion weregiven by many practical chemilts, the truenature of the Epfom fait was not fully under-ftcod till Dr. Black, in 17 "5, Ihcwcd, in themolt convincing manner, that it confided ofmagnefia, combined with the vitriolic acid, andobtained the magnefia irom it by means.of analkali.

This condition of the two faits was furtherpromoted by a fraud commonly praftifed on theContinent / where the Englilh or Epfom fait was

32, p. y Pkil, Journ. vol 3. w Ibid. vol. 5.

3 C 2