By evaporation to dryness, an imperial gallon left a solid residue, weighing 17·33 grs., which consisted of—
| Carbonate of lime, with a little oxide of iron | 11·12 |
| Carbonate of magnesia | 0·60 |
| Sulphate of lime | 1·56 |
| Chloride of sodium | 2·40 |
| Silicic acid | 0·37 |
| Organic matter | 1·19 |
| 17·24 |
When heated, this water became turbid; and, by continued boiling for two hours in an apparatus so arranged that the whole of the steam was condensed and returned to the water, 10·95 grs. of the earthy carbonates, coloured by oxide of iron, were deposited.
The relative hardness of this water, as determined by the soap test, distilled water being taken as unity, was 13·3.
B. The second sample of water was taken from a small tap in the house of Mr. Hall, Bishopsgate-street. The tap was attached to the main.
This water was without smell or taste, and free from floating matter. After standing some time, it deposited a very small quantity of oxide of iron. Although clear and transparent, it was not bright.
It contained 19·10 grs. of solid matter in the imperial gallon. The solid matter consisted of—
| Carbonate of lime, with a little oxide of iron | 14·58 |
| Carbonate of magnesia | 0·44 |
| Sulphate of lime | 1·54 |
| Chloride of sodium | 1·71 |
| Silicic acid | 0·32 |
| Organic matter | 0·72 |
| 19·31 |
Like the preceding water it became turbid when heated to the boiling point, and by continued ebullition for two hours, 12·90 grs. of carbonate of lime, coloured by oxide of iron, were precipitated.
Hardness in reference to distilled water as unity = 19.