| Real acid | 36.90 | or | 80 |
| Water | 9.23 | 20 | |
| 46.13 | 100 |
The salt remaining in the retort weighed 92.87 parts; nearly this weight of water being added and heated, the whole was dissolved, and on cooling, a salt, consisting of extremely minute filaments resembling asbestos, was obtained, which, by capillary attraction, retained a part of the residual solution so powerfully, that it was necessary to absorb it by filtering paper.
Although it appeared improbable that the crystals could be a variety of the known form of bisulphate of potash, yet supposing it might be that salt with either less, or more than two atoms of water, Mr. Phillips proceeded to its analysis. Some of the salt was readily dried by exposure to the air of a warm room: 100 grains, by muriate of baryta gave 154.75 grains of sulphate of baryta, equivalent to 52.45 sulphuric acid: 109 grains heated to redness, lost 21.6 sulphuric acid and water, and left 78.4 grains of neutral sulphate of potash. The latter contain 35.6 grains of sulphuric acid, which, subtracted from the whole quantity of 52.45, indicates 16.85 as the quantity dissipated by heat; and this again, subtracted from the 21.6, indicates 4.75 water in the crystals. The quantity of acid separated by heat is, therefore, very nearly half that remaining in the neutral sulphate, and the salt in question appears to be a sesquisulphate of potash, consisting of
| theory. | exper- iment. | ||||
| 3 atoms sulphuric acid | 120 | 55.33 | 52.45 | ||
| 2 atoms potash | 96 | 42.66 | 42.80 | ||
| 1 atom water | 9 | 4.00 | 4.75 | ||
| 225 | 99.99 | 100.00 |
Mr. Phillips found it difficult to prepare the sesquisulphate free [p468] from bisulphate; and on repeating the attempt to procure it exactly as before, obtained a large quantity of bisulphate, and a small quantity of the peculiar salt; although the quantity of water present is known to have an important influence on the nature of the sulphates produced, yet the precise circumstances on which the formation of sesquisulphate depends, are at present unknown.—Phil. Mag. N. S., ii. 429.
10. On certain Properties of Sulphur.
Fused sulphur began to crystallize between 226° and 228°. Its fusing point may be considered as 226°.4. Between 230° and 284° it is as liquid as a clear varnish, and of the colour of amber; at about 320° it begins to thicken, and acquire a red colour; on increasing the heat, it becomes so thick, that it will not pour. This effect is most marked between 428° and 572°; the colour being then a red-brown. From 572° to the boiling point it becomes thinner, but never so fluid as at 248°. The deep red-brown colour continues until it boils.
When the most fluid sulphur is suddenly cooled, it becomes brittle, but the thickened sulphur, similarly treated, remains soft, and more soft as the temperature has been higher. Thus, at 230°, the sulphur was very liquid, and yellow; and cooled suddenly by immersion in water, it became yellow and very friable; at 374° it was thick, and of an orange colour, but by cooling, became at first soft and transparent, but soon friable, and of the ordinary appearance; at 428°, it was red and viscid, and when cooled, soft, transparent, and of an amber colour; at the boiling point it was deep brown red colour, and when cooled very soft, transparent, and of a red-brown colour.
It is not necessary, as is sometimes stated, to heat the sulphur a long time to produce this effect; all depends upon temperature. The only precaution necessary is, to have abundance of water, and to divide the sulphur into small drops or portions, that the cooling may be rapid. If it be poured in a mass, the interior cools slowly, and acquires the ordinary hard state. When the experiment is well made at 446°, the sulphur may be drawn into threads as fine as a hair, and many feet in length.
M. Dumas, in remarking upon this curious effect of sudden cooling, classes it with the similar effect which occurs with bronze. Although difficult to assign the exact cause, yet he notices that the tendency to crystallize can evidently be traced as influential over some of the appearances, the hardness and opacity, for instance, [p469] which always occur together when the crystalline state is assumed; whereas, when rapid cooling has hindered crystallization, the mass remains soft and transparent, until it crystallizes, which usually happens in twenty or thirty hours.—Ann. de Chimie, xxxvi. 83.