For cleaning gravel walks any of the following may be used :

I

Gas-tar liquor.

II

Rock salt (cattle salt).

III

Hydrochloric acid.

IV

Sulphuric acid.

V

Fresh limewater. The gas-tar liquor must be poured out a few times in succession, and must not touch the tree roots and borders of the paths. This medium is cheap. Cattle salt must likewise be thrown out repeatedly. The use of hydrochloric and sulphuric acids is somewhat expensive. Mix 60 parts of water with 10 parts of unslaked lime and 1 part of sulphuric acid in a kettle, and sprinkle the hot or cold mixture on the walks by means of a watering pot. If limewater is used alone it must be fresh —1 part of unslaked lime in 10 parts of water.