Chloride of Calcium from Marble and Spirit of Salt

Weigh the marble and the hydrochloric acid. The notebook (step 6) works out the amounts: 1 kg of marble takes about 2.3 kg of acid at specific gravity 1.162.

Put the acid in a large glass jar and add the marble a little at a time, stirring. It fizzes as carbon dioxide escapes, so leave plenty of room in the jar. When a fresh pinch no longer fizzes, the acid is used up; let any undissolved marble settle and pour the clear solution off.

Evaporate the solution in a pan until it is strong. On cooling, the salt separates as colourless prismatic crystals, which hold 6 parts of water to each part of the chloride (Fownes).

Heat the crystals to expel their water. Raised to a strong red heat in a crucible, the dry salt fuses; cast or broken into pieces, fused chloride is the form used to dry gases.

The crystals are exceedingly deliquescent: left open they take water from the air and run to a liquid. Store the salt hot from drying in a stoppered jar.

Fownes (1856) names marble dissolved in hydrochloric acid as the usual source and adds that calcium chloride is also a by-product of several manufactures; Ure (1839) notes it as the residue of making ammonia from sal ammoniac and lime. Fownes gives no quantities; those in the notebook come from the equation. Testing for the end of the fizzing, and leaving room in the jar, are ordinary practice, not his words.