FIXING AND CLEARING 127 
cases to convert these salts into tetrathionates ; and, as a nega- 
tive or print can be practically freed from hypo in half an 
hour by proper washing, their use is only allowable in cases of 
great pressure of time or shortage of fresh water. The fol- 
lowing have been recommended. 
Zinc hypochlorite (Hart).— 
Chloride of lime 10g 77 gr. 
Water 500 ccm 8 oz. 
Rub the lime into a cream with a little water; then add the 
rest of the water, and add to: 
Zinc sulphate 20 g 154 gr. 
Water 500 ccm 8 oz. 
Shake well and filter or allow to stand until the precipitate 
subsides, and decant the supernatant liquid. For use dilute 
with 9 parts of water; immerse the negatives or prints for 
about 3 minutes, and then briefly wash and dry. Sodium or 
potassium hypochlorites may be made and used in the same 
way, employing the alkaline carbonates instead of the zinc 
salt. 
Potassium permanganate, in 1 per cent solution, may also be 
used, enough being added to water to give a pink tinge, and 
the negatives bathed in the solution until the colour is no 
longer discharged, repeated baths being used. Potassium 
percarbonate in 1 per cent solution has also been sold com- 
mercially as Hypax or Hypono. Sodium perborate can be 
used in the same way. Potassium or ammonium persulphate 
in 1 per cent solution, made alkaline with ammonia, may also 
be used. The former has been sold as Thioxydant, Anthion, 
etc. A 5 per cent solution of hydrogen peroxide may also be 
used. 
HARDENING BatHs.—Sometimes used for negatives and 
prints in hot weather. Thorough washing so as to eliminate 
all hypo must precede these baths: 
