If all the chlorine made in one operation is not at once required for the manufacture of a colour, it can be utilised by sending it into a box filled with slaked lime, which is converted into chloride of lime or bleaching powder. The liquid run away from the apparatus at the conclusion of the operation contains manganese and sodium sulphates, or manganese chloride as the case may be, and can be used for the preparation of manganese pigments. =Ammonia=, NH₃ = 17.—Ammonia is obtained from chemical works in the form of a strong solution of ammonia gas in water, which is generally very pure. The density of an aqueous solution of ammonia is the smaller the more ammonia it contains, and thus the strength of a solution of ammonia can easily be formed by means of the hydrometer. The following table shows the percentage of ammonia, NH₃, in a liquid of known specific gravity at the temperature of 14° C.:— +-------------+------------+------------+------------+ | Specific | Ammonia | Specific | Ammonia | | Gravity. | per cent. | Gravity. | per cent. | +-------------+------------+------------+------------+ | 0·885 | 36·00 | 0·953 | 11·50 | | 0·886 | 35·00 | 0·955 | 11·00 | | 0·889 | 34·00 | 0·957 | 10·50 | | 0·891 | 33·00 | 0·959 | 10·00 | | 0·893 | 32·50 | 0·961 | 9·50 | | 0·895 | 32·00 | 0·963 | 9·00 | | 0·897 | 31·30 | 0·965 | 8·50 | | 0·900 | 26·00 | 0·968 | 8·00 | | 0·905 | 25·39 | 0·970 | 7·50 | | 0·925 | 19·54 | 0·972 | 7·00 | | 0·932 | 17·52 | 0·974 | 6·50 | | 0·947 | 13·46 | 0·976 | 6·00 | | 0·951 | 12·00 | 0·978 | 5·50 | +-------------+------------+------------+------------+