Page:Proceedings of the Royal Society of London Vol 1.djvu/379

Rh gravities, by putting equal weights successively into the same vessel, and again weighing it after ﬁlling the interstices with a saturated solution of salt. The difference between the large-grained ﬁshery salt and the bay- salt of foreign manufacture is so inconsiderable, that although the superiority of the former in chemical purity may not be considered as of any advantage for economical purposes, yet in its mechanical qualiﬁes it cannot be said to be inferior in a degree that can be pre-judicial.

The methods of analysis employed by the author in this inquiry are next described. The salt to be examined was ﬁrst dried ata. given temperature of 180°. The earthy muriates were then sepa- rated by alcohol, and their aggregate weight ascertained after evapo- ration of the alcohol. An aliquot part was next dissolved, and the lime precipitated ﬁrst by carbonate of ammonia, after which the mag- nesia was separated by phosphate of soda, as a triple ammoniacal phosphate of magnesia. A previous trial having shown that 100 grains of dry muriate of magnesia would give 151 of the triple phosphate, the quantity of muriate of magnesia was inferred from this latter precipitate, and the difference between that and the ag- gregate weight of the two rnuriatcs was considered as muriate of lime. Sometimes the estimation was formed in a diﬁ‘erent way, by superoxalate of potash, which was found to occasion a precipitate of 116 grains from 100 dry mnriate of lime ; and thence, as before, the weights of each might be inferred.

For estimating the earthy sulphates, the quantity of original salt that remained after affusion of alcohol was dissolved by long boiling in water; the earths were precipitated as carbonates by carbonate of soda. The sulphuric acid was separated by muriate of barytes, and thence estimated. The earths were then re-dissolved in sulphuric acid. dried, and their weight ascertained. Of these sulphates, the more soluble part was dissolved in a small quantity of warm water, and the magnesia precipitated, as in the former case, as a triple phosphate of magnesia.

It was found that 100 grains of this precipitate indicate 111 of crystallized sulphate of magnesia; and hence the respective quantities of the two sulphates was known: but since it was possible that some proportion of alkaline sulphates might be also present, some collateral experiments were necessary for the purpose of ascertaining whether the sulphuric acid obtained above by muriate of barytcs, corresponded with that which would be containcd in the mere quantities of sulphate of magnesia and sulphate of lime discovered