232 C H E M 
and larger than thofe of fulphat of (oda; and it likewife 
differs from that perfect neutral lalt in all its other pro 7 
perties. 
This frit has a very bitter tafle, and on that account 
has been called fal catbarticus amarus. All the bitter 
fait waters are commonly folutions more or lefs ftrong of 
fulphat of magneiia. It is of a greyifh-white colour, 
not very bright. Expofed to heat, it lol'es almoH.all its 
water of cryftaliization, which reduces it to little more 
than half its weight: it admits of the aqueous fufion. 
With an extreme heat it undergoes the igneous fufion, 
but is not decompofed ; if, after being melted, it be pour¬ 
ed into a veffel, it recovers moifture from the air, and 
burfts the veffel which contains it. It is llightly efflorel- 
cent in a very dry air. It is fo foluble in water, that only 
twice its weight of cold, and half its weight of hot, wa¬ 
ter, are required to hold it in lolution. 
To decompofe this fulphat with charcoal, mix it with 
one-eighth of its weight of charcoal-dull; put this mix¬ 
ture into a Hone retort, to which a bent tube is adapted 
going under a jar in the gas apparatus before defcribed. 
By the aid of caloric, or heat, the charcoal i'eizes upon 
the oxygen of the fulphat, and fulphure of magneiia is 
produced. The heat mull be applied gently, that the 
fulphure itfelf may not be decompofed, for the fulphur 
has but little attraction for the magnefia: carbonated 
hydrogen gas paffes under the jar, which arifes from the 
water of the decompofed Cubfiances. By pouring ful- 
phuric acid over this folution of the fulphure. of mag¬ 
nefia, fulphat of magneiia is re-'produced, and pure ful¬ 
phur is obtained by filtration. Then the magnefia may be 
extracted from the lolution of the newly-formed fulphat, 
by adding caullic alkali. T he liquor holds the fulphur 
much divided, and palfes through in draining, but be¬ 
comes flaky in boiling. 
By adding to luiphat of magnefia a little fulphuric 
acid, a fulphat of magnefia is produced with an excels 
of acid ; and, by pouring on ammoniac, no precipitate 
is formed, becaufe the ammoniac does not decompofe 
this acidified fulphat of magnefia, but forms a tripie fait. 
Barytes decompoles this fait, by taking away the fulphu¬ 
ric acid. If barytes diffolved in pure water be made ufe 
of, the fulphat of barytes and the magnefia are precipi¬ 
tated together} but, if an acid folution beufed, as mu- 
riat of barytes for example, the luiphat of barytes will 
be precipitated, and the magnefia remain in the liquor 
in the date of muriat of magnefia. 
Sulphat of magneiia is in the lame manner decompofed 
by potalh and foda. Caudic potafli precipitates the mag¬ 
nefia in very pure white flakes, and luiphat of potalh is 
obtained. Lime precipitates the magneiia from the ful¬ 
phat of magnefia : a fulphat of lime is produced. 
Ammoniac decompoles, cold, part of the luiphat of 
magneiia ; but the precipitate is flight, and all the mag¬ 
nefia is not feparated; for if, after filtration, the liquor 
be tried with potalh, another precipitation is produced. 
If the liquor is left to evaporate (lowly, a triple fait is 
formed, the ammoniaco-magnefian fait, or fulphat. This 
fait is bitter, with an urinous talte; is leis loluble than 
fulphat of ammoniac, but more fo than fulphat of mag¬ 
nefia; it crydallizes in dodecahedrons, fometimes four- 
lided. It is decompofed by heat. The prefence of the 
ammoniac in this fait may be known by triturating or 
pounding it with lime. The magneiia may be dil'cerned 
by precipitating it with a caullic alkali; by adding after¬ 
wards lime and a little water, the odour of ammoniac is 
difengaged. When this triple lalt is urged with a fircng 
heat, the ammoniacal fulphat evaporates., and .fulphat of 
magnefia remains at the bottom of the retort. The am- 
moniaco-magnefian lalt may be directly formed, by mix¬ 
ing together the lolutions of fulphat of magnefia and 
fulphat of ammoniac. The liquor immediately grows 
turbid, and loon alter cryltallizes. 
S.ulphat of Gi.ucine. —Glucine combines very well 
with fulphuric acid, whether free or in the Hate of car- 
bonat; in the latter cafe, a brilk effervefcence is produc- 
I S T R Y. 
ed. The fait refulting from this combination is very fij- 
luble in water, fo that in melting it becomes as thick as 
a fyrup before it cryltallizes. Its talle is very laccharine, 
and llightly aftringent. Expofed to heat it (wells up like 
alum ; and in a red heat wiil be entirely decompofed ; 
the fulphuric acid flies off in vapours, and the earth re¬ 
mains pure. 
Charcoal decompofes it with the aid of heat, and a 
fulphure is produced. No acid will decompofe this fair; 
hence it appears that (ulphuric acid has a greater affinity 
for this earth than any other. Alkalis and earths, except 
alumine, decompofe it, by feizing on the (ulphuric acid, 
for which they have a flronger attraction. 
Sul?h,t of Alumine. —There are feveral kinds of ful¬ 
phat of alumine: the molt common in the acid fulphat of 
alumine, or the alum of commerce. It is found about vol¬ 
canos, on lavas, and on rocks in feveral places. To ob¬ 
tain luiphat of alumine, the alum-ore is expoTed to the 
wind and rain, or it may be burnt: the fulphur contain¬ 
ed therein forms, by its union with the oxygen which it 
abforbs, fulphuric acid, and unites with the alumine : 
combine the whole in water, and heat it, leave it to 
grow cold, and you have pure acid fulphat of alumine. 
A little alkali is generally mixed with it, whether afhes, 
fulphat of potafli, or even (tale urine; all thefe falts are 
neceflary to obtain it in the cryllallized (late, and to take 
away its vifcofity. Hence it is, that, according to Vau- 
quelin, (Annales de Chimie, tom. xxii.) (peaking of the 
different ffates of the combination of alumine with ful¬ 
phuric acid, which are at the fame time united with dif¬ 
ferent bales, we are to diftinguifti feven different Hates 
of this combination, i. Sulphat of alumine, or the arti¬ 
ficial union of fulphuric acid and alumine. This fait is 
afiringent, it cryltallizes in (oft plates or leaves, loluble 
in water ; and was not known till lately, a. Acid fulphat 
of alumine, or the preceding lalt with anexcefs of theacid, 
and differs from it only in a reddening blue vegetable co¬ 
lours. It is eafily formed, by diffolving the preceding 
fulphat in fulphuric acid ; but it is with great difficulty 
converted into neutral fulphat of alumine, namely, by 
boiling it a long time with its earth. This fait has not 
been hirherto delcribed, any more than thefirff. 3. Sul¬ 
phat of alumine and faturated potafli : this is the alum 
of the chemiffs faturated with its earth. Its properties 
are, pulverulence, infipidity, infolubility, that it will 
not cryftallize, but is eafily converted into true alum by 
the fulphuric acid. 4. Acid luiphat of alumine and pot¬ 
afli. It is eafy to prepare this chemically, and it greatly 
refembles common alum ; but Vauquelin only found that 
of Tolfa to be of this kind. 5. Acid fulphat of alumine 
and ammoniac. This is eafily made in a laboratory; but 
in commerce it is never met with pure. 6. Acid fulphat 
of alumine, potafli, and ammoniac. This is the kind 
of alum moff commonly ufed in manufa£iures: we dial 1 
therefore call it alum, for diffinclion-lake. 7. Acidulat¬ 
ed fulphat of alumine and potafli. Vauquelin propofes 
this name, becaufe, by adding to the folution a little 
more potafli than is required to obtaineight-fided crvffals, 
it affumes the cubical form. 
Of th t alum of commerce, (or acid fulphat of alumine, 
potalh, and ammoniac, as mentioned at No. 6.) there 
are feveral fpecies: 1. Rock-alum, called by La Grange, 
alun de glace, alum of ice, is found in confiderable ni a fi¬ 
fes ; tranfparent. Bergman thinks that this name is de¬ 
rived from the city of Rocca, in Syria, now called Edefla, 
where the molt ancient manufadture of this fait was efia- 
bliflied, and not becaufe its form refembles a rock, or 
Hone, or becaufe it is obtained from rocks or Hones, as 
feveral authors have affirmed. This fpecies of alum is 
very impure. 2. Roman alum, which is prepared in the 
territory of Civita Veccliia, and obtained from a place, 
named in Italian, Aluminiere della Haifa. This alum is 
in pieces of the fize of eggs; it is covered with a reddifli 
efflorefcence, and is fuppofed to be pure when that efflo- 
relcence is feparated. 3. Naples alum, extradted from a 
peculiar earth at the Solfaterra ; it is in larger mafl'es than 
