Analysis of the calcareous tuffa at Green Point

Abstract

This article is a letter from J. H. Trepgorp to Dr A. Smith, detailing the chemical analysis of a specimen of calcareous tuffa (limestone) collected from Green Point, Cape Town (Cape Colony).

The author performed several experiments on 100-grain samples of the stone:

1. Sulphuric Acid Treatment: This method isolated and measured the Aluminous earth content, which was determined to be 4 grains (4%).

2. Nitric Acid Treatment: This experiment measured the volatile components and the insoluble residue. It expelled 38 grains of Carbonic Acid and left 12 grains (12%) of Siliceous earth undissolved.

3. Calcination: By heating the sample, the total loss of mass was 42 grains. Allowing 4 grains for water, the remaining 38 grains confirm the proportion of Carbonic Acid.

From these results, Mr Trepgorp concluded the approximate composition of the stone per 100 lbs. is:

• Carbonate of Lime: ≈ 84 lbs.

• Siliceous Earth: 12 lbs.

• Aluminous Earth: 4 lbs.

• (Including a small portion of water)

The analysis identifies the stone as being primarily Carbonate of Lime.