If added too quickly the hydrosulphite will cake, fall to the bottom and be difficult to dissolve.
The constituents of the hydrosulphite vat are hydrosulphite of soda, lime and indigo.
It has many advantages over the hydrosulphite vat, as it is not nearly so much affected by changes of temperature and weather.
Here again the hydrosulphite takes up oxygen from the water and liberates the necessary hydrogen.
It may be restored to its former conditions by adding some hydrosulphite of soda.
The hydrosulphite of soda referred to above is made in the following way: 4-1/2lb.
Of such vats the copperas and lime and the hydrosulphite vats are examples.
This may most conveniently be done by adding thereto a solution of hydrosulphite of soda, which may be made by mixing 4½ lb.
Cotton is dyed by means of the "lime and copperas vat," the "zinc powder vat," or the "hydrosulphite vat."