366 'Sulphite of Magntfta-'of Baryfts—oJ Aliimhe. 



Metallic folutions decompofe it, at Icaft for the mod patf. 



The quintal contains — i. Lime 47; — 2. Sulphuric acid 485—3. Water j. 



Sulphiti of Magtiefia.'] This fait is white and traniparcnt. ~ Its form a deprefled tetra- 

 hedron ; its taftc is mild and earthy at firft, and afterwards fulphureous. 



By expofure to heat, it foftens, fwells up, and becomes dutlile, like gum ; it iofes about 

 0,45 of its weight by the deficcation. 



If the heat be kept up after it has loft its water of cryftallization, the fulphureous acid 

 flies off, and the refidue in the retort is magnefia, nearly pure. In this way we found that 

 a quintal of this fait is compofed of 16 parts magnefia, 39 fulphureous acid, and 45 water. 



This fait is fparingly foluble in water, but very folublc in an cxcefs of acid ; and this fo- 

 lution, expofed to the air, cryftallizes very readily, by lofing its excefs of acid. 



It becomes opake in the air, and changes by degrees into fulphate ; but for this purpofc 

 much time is required. 



The fixed alkalis, lime and barytes, decompofe it completely ; ammoniac decompofes it 

 in part only, and a triple fait is formed. 



The alkaline and earthy falts, except thofe of alumine, decompofe it likewife. 



The mineral acids and metalUc folutions produce the fame effeds on this fait as on the 

 other fulphites. 



Sulphite cf Barytes."] This fait does not cryftallize, has no perceptible tafte, and is per- 

 feftly infolubic in water. For this rcafon the fulphureous acid carries down a precipitate 

 from the aqueous folution of barytes. It is not rendered foluble by an excefs of acid, like 

 the other earthy fulphites. 



Heat changes it into fulphate ; but it docs not pafs to this (late by expofure to tlie air, but 

 ■with extreme difficulty. 



No earth nor alkali decompofes it. 



The acids decompofe it ; whence the fulphureous acid does not precipitate the barytic 

 falls, as the fulphuric acid does. 



Among the neutral falls there are none but the alkaline carbonates which decompofe it. 



The other properties of this fait are fuch as are cornmon to the fulphites*- 



It is compofed of — I. Barytes 595—2. Sulphureous acid 39; — 3. Water 2. 



Sulphite of Alumitie.'] It is infoluble in water, but becomes abundantly fo by excefs of 

 acid. Its diflblution does not cryftallize by the contaiSI: of air, and becomes converted into 

 a foftidi duclile mafs. 



Fire difengages the fulphuric acid witliout alteration. 



All the alkalis and earths decompofe it, as do alfo the mineral acids. 



Its component parts are — 44 alumine, 32 fulphureous acid, and 24 water. 



From the fa£ls defcribed in this memoir it is evident that the fulphites poITcfs very dif- 

 ferent properties from thofe of the fulphatcs; and that they follow peculiar laws of foI,utio!i, 

 cryftallization, affinity, and decompofition. 



In faft they poflefs — 1. A fulphureous tafte, fimilar to that of their acid. 2. Tliey arc 

 ilecompofable by fire, either by the efcape of their acid without alteration, or by lofing a 

 portion of fulphur and becoming converted into fiilphates. 3. They are converted into ful- 

 phatcs by the conta£l of air, or of any other fubftance capable of affiirding oxypene; and their 

 weight is increafed by this converfion. 4. They are decompofed by moft acids; which expel 



tlie 



