On definite Proportions. 171 
nor did it become turbid upon the addition of ammonia. When 
evaporated, together with the water used for washing the powder, 
in a platina crucible, and ignited, it afforded 1-515 gr. of sul- 
phate of potass, answering to -981 gr. of potass. 
Since we have seen that alumina contains about 46°7 per cent. 
of oxygen, it is impossible that the bases can here contain equal 
parts of oxygen. Alum, according to these experiments, is thus 
constituted : 
Sulphuric acid.. 34°23 Or, 
Alumina ...... 10°86 - Sulphate of alumina 36°85 
GAG ss atl PBL Sulphate of potass.. 18-15 
Water ........ 45°00 Water cule «0s 1 seaanon 
Now, 9-81 parts of potass neutralise 8°37 of sulphuric acid, 
and 25-86 parts of sulphuric acid remain for the alumina: con- 
sequently the alumina saturates in the alum three times as much 
acid as the potass, for 8°37 x 3=25'11; so that the alumina 
must contain three times as much.oxygen as the potass. But 
9-81 parts of potass contain 1-674 of oxygen, and 10-86 of 
alumina 5-077; and 1-674 3=5-022. The 45 parts of water 
contain 39-71 of oxygen, and 5-022 x8=40°17. It is true that 
this analysis is not correct to the last places of decimals: but it 
is at least sufficient to prove, that in alum the alumina contains 
three times as much oxygen as the potass; and in this instance 
we have a double salt, in which the oxygen of one of the bases is 
an integral multiple of that of the other. 
Since the proportion of the alumina to the sulphuric acid, in 
this analysis, agrees as nearly as possible with that which was 
found in the neutral sulphate, it is impossible that alum should be 
a supersalt; but it is indebted for its acid properties to the weak 
attraction of the alumina to the sulphuric acid which belongs to it; 
the sulphate of alumina preponderating so much above that of 
potass, that it communicates to the compound almost all its out- 
ward characters. 
Alum and the other double salts afford us interesting examples 
of the combinations of more than two oxygenized bodies. ‘The 
potass here contains the smallest quantity of oxygen, which must 
therefore be the common divisor for the quantities contained in 
the other component parts. If we call this quantity 1, the alu- 
mina will contain 8, the sulphuric acid 12, and the water 24. 
Finally, 1 must observe, that my analysis of alum difiers in 
some measure from that of Thenard and Roard. These chemists 
found in alum 124 per cent. of alumina, and only 16 per cent. of 
sulphate of potass. [Vauquelin found the component parts al- 
ways 10-5 of alumina, 10:4 of potass, 30°52 of sulphuric acid, 
and 48-58 of water: the acid and the water taken together agree 
’ nearly with Berzelius’s result: the alumina is a little less, per- 
haps 
