The third portion throws down another portion or atom of alumine; but by continued agitation the two atoms of alumine liberated, join the remaining atom of sulphate of alumine, and the whole compound falls down, being then the common subsulphate of alum. Hence the liquid, containing nothing but sulphate of lime and sulphate of potash, is neutral by the test, and yields no alumine by the addition of lime water. The fourth portion of lime water being put in and duly agitated, the atom of sulphuric acid is drawn from the subsulphate to join the lime, and then the floating subsulphate of alumine becomes pure alumine, and the clear liquor is still neutral. The fifth portion of lime water tries to decompose the sulphate of potash, but is unable of itself; however, the floating alumine assists it, and by double affinity the potash leaves the acid to join the alumine, and the lime takes the acid. Hence as ⅓ of the alumine enters into solution with the potash, the precipitate is less copious, and the liquid is alkaline; a small portion of acid put into the clear liquid engages the potash, and liberates the alumine, but a larger portion redissolves the alumine also. The sixth portion of lime water seems to complete the effect which the fifth commences, and hence the density of the liquid increases, whilst the precipitate rather diminishes. The seventh portion of lime, together with the sixth, after due agitation and some time, unite the lime with the alumine, one atom of each, and form a precipitate which would fall together, were no other compound present, as I found, and Scheele before me; but if sulphate of lime be present, each compound atom of lime and alumine, unites with one of sulphate of lime, and the whole descends together, forming a subsulphate resembling that of alum, only two atoms of lime are found as substitutes for two atoms of alumine. This subsalt is very little soluble in water. According to this view, if 2 atoms of alum were decomposed, 4 atoms of subsulphate would be formed, each consisting of 1 acid, 2 lime, and 1 alumine; also 2 compound atoms of potash and alumine, and 6 atoms sulphate of lime. But in the final arrangement, it would seem, that 2 atoms of sulphate of lime are again decomposed, and sulphate of potash formed, the 2 atoms of lime combining with the 2 of alumine, and then two more atoms of subsulphate are formed, and the final arrangement is 6 atoms subsulphate precipitated, and 2 atoms sulphate of potash, and 2 sulphate of lime remain in solution. The facts above stated appear to me to place the constitution of alum in a clearer point of view than any other I have seen. They make no difference in the weights of the several elements in 100 grains of the salt, from what we have given in Vol. 1; only the weight of the atom of alumine is here taken to be 20 instead of 15, and we have 3 atoms of it in 1 of alum, instead of 4, as in the former account. ON THE PRINCIPLES OF THE ATOMIC SYSTEM OF CHEMISTRY.